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1 13-1 CHAPTER 13 Radiate Animals

2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-2

3 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-3 Phylum Cnidaria Phylum Cnidaria Over 9,000 species in the phylum Cnidaria Over 9,000 species in the phylum Cnidaria Equipped with specialized cells: cnidocytes Equipped with specialized cells: cnidocytes Contain a specialized stinging organelle, the nematocyst Contain a specialized stinging organelle, the nematocyst Fossil specimens dated to over 700 million years ago Fossil specimens dated to over 700 million years ago Extant species Extant species Most common in shallow marine environments Most common in shallow marine environments Some freshwater Some freshwater None are terrestrial None are terrestrial

4 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-4 Phylum Cnidaria Some ctenophores, molluscs and flatworms eat hydroids and use the stinging nematocysts for their own defense Some ctenophores, molluscs and flatworms eat hydroids and use the stinging nematocysts for their own defense Four classes of Cnidaria Four classes of Cnidaria Hydrozoa Hydrozoa Scyphozoa Scyphozoa Cubozoa Cubozoa Anthozoa Anthozoa A fifth class, Staurozoa, has been proposed A fifth class, Staurozoa, has been proposed No medusae in life cycle but polyp topped by medusa-like region No medusae in life cycle but polyp topped by medusa-like region

5 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-5 Phylum Cnidaria Characteristics of Phylum Cnidaria All are aquatic and mostly marine All are aquatic and mostly marine Symmetry Symmetry Radial or biradial Radial or biradial Two body types Two body types Free-swimming medusae Free-swimming medusae Sessile polyps Sessile polyps Diploblastic Diploblastic Epidermis and gastrodermis Epidermis and gastrodermis Mesoglea: extracellar matrix that lies between ectodermis and gastrodermis Mesoglea: extracellar matrix that lies between ectodermis and gastrodermis

6 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-6 Phylum Cnidaria Incomplete gut: gastrovascular cavity Incomplete gut: gastrovascular cavity Extracellular digestion in gastrovascular cavity Extracellular digestion in gastrovascular cavity Intracellular digestion in gastrodermal cells Intracellular digestion in gastrodermal cells Tentacles usually encircle mouth or oral region Tentacles usually encircle mouth or oral region Muscular contractions via epitheliomuscular cells Muscular contractions via epitheliomuscular cells Outer layer of longitudinal fibers and an inner layer of circular fibers Outer layer of longitudinal fibers and an inner layer of circular fibers Sense organs for balance (statocysts) and photosensitivity (ocelli) Sense organs for balance (statocysts) and photosensitivity (ocelli)

7 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-7 Phylum Cnidaria Nerve net Nerve net Symmetrical and asymmetrical synapses Symmetrical and asymmetrical synapses Diffuse conduction Diffuse conduction Two nerve rings in hydrozoan medusae Two nerve rings in hydrozoan medusae Asexual reproduction Asexual reproduction Budding in polyps Budding in polyps Some colonies exhibit polymorphism Some colonies exhibit polymorphism Sexual reproduction Sexual reproduction By gametes in all medusae and some polyps By gametes in all medusae and some polyps Monoecious or Dioecious; Monoecious or Dioecious; Holoblastic indeterminate cleavage Holoblastic indeterminate cleavage No excretory or respiratory system No excretory or respiratory system Acoelomate Acoelomate

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10 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-10 Phylum Cnidaria Form and Function Cnidaria have two basic body plans: polyp and medusa Cnidaria have two basic body plans: polyp and medusa Polyp Polyp Hydroid form Hydroid form Adaptation to a sedentary life Adaptation to a sedentary life Tubular body with the mouth directed upward and surrounded by tentacles Tubular body with the mouth directed upward and surrounded by tentacles Mouth leads into a blind gastrovascular cavity Mouth leads into a blind gastrovascular cavity Aboral end attached to substratum by pedal disc Aboral end attached to substratum by pedal disc Reproduce asexually by budding, fission, or pedal laceration Reproduce asexually by budding, fission, or pedal laceration

11 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-11 Phylum Cnidaria In colonial forms In colonial forms Polyps may be specialized for feeding, reproduction, or defense Polyps may be specialized for feeding, reproduction, or defense In class Hydrozoa In class Hydrozoa feeding polyps (hydranths) distinguished from reproductive polyps (gonangia) by absence of tentacles in gonangia feeding polyps (hydranths) distinguished from reproductive polyps (gonangia) by absence of tentacles in gonangia

12 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-12 Phylum Cnidaria Medusa Medusa Bell or umbrella ‑ shaped Bell or umbrella ‑ shaped Usually free-swimming Usually free-swimming Mouth directed downward Mouth directed downward Tentacles may extend down from rim of umbrella Tentacles may extend down from rim of umbrella Medusae equipped with statocysts and ocelli Medusae equipped with statocysts and ocelli Integration of sensory information into motor response Integration of sensory information into motor response Function of a nerve ring located at base of the bell Function of a nerve ring located at base of the bell Velum differentiates hydromedusae from scyphomedusae Velum differentiates hydromedusae from scyphomedusae Shelf-like fold of tissue from the bottom of the bell that extends into the bell Shelf-like fold of tissue from the bottom of the bell that extends into the bell

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14 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-14 Life Cycles Polyps and medusae play different roles in the cnidarian life cycle Polyps and medusae play different roles in the cnidarian life cycle Typically, zygote develops into a motile planula larva Typically, zygote develops into a motile planula larva Planula settles, and metamorphoses into a polyp Planula settles, and metamorphoses into a polyp Produce other polyps asexually Produce other polyps asexually Polyps eventually produce a free-swimming medusa by asexual reproduction Polyps eventually produce a free-swimming medusa by asexual reproduction Budding or strobilation Budding or strobilation Phylum Cnidaria

15 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-15 Phylum Cnidaria Medusae Medusae Dioecious Dioecious Reproduce sexually Reproduce sexually True jellyfish (class Scyphozoa) True jellyfish (class Scyphozoa) Medusa is large and conspicuous Medusa is large and conspicuous Polyps typically very small Polyps typically very small Most colonial hydroids Most colonial hydroids Feature a polyp stage and a pelagic medusa stage Feature a polyp stage and a pelagic medusa stage Some hydrozoans (Physalia) form floating colonies Some hydrozoans (Physalia) form floating colonies In Hydra, only stage is a small freshwater polyp In Hydra, only stage is a small freshwater polyp

16 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-16 Phylum Cnidaria Body Wall Cnidarian body Cnidarian body Outer epidermis Outer epidermis Inner gastrodermis Inner gastrodermis Layers separated by mesoglea Layers separated by mesoglea Mesoglea Mesoglea Gelatinous (at least 95% water) Gelatinous (at least 95% water) Continuous in polyps, extending through body and tentacles Continuous in polyps, extending through body and tentacles Supports body Supports body Thick in anthozoans, and scyphozoan medusae Thick in anthozoans, and scyphozoan medusae Thinner in hydromedusae Thinner in hydromedusae

17 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-17 Phylum Cnidaria In Hydra In Hydra Epidermis contains epitheliomuscular, interstitial, gland, sensory, and nerve cells Epidermis contains epitheliomuscular, interstitial, gland, sensory, and nerve cells Cnidarian bodies extend contract, bend, and pulse Cnidarian bodies extend contract, bend, and pulse No mesodermally derived muscle cells No mesodermally derived muscle cells Have epitheliomuscular cells Have epitheliomuscular cells Form most of epidermis Form most of epidermis Cover organism and function in muscle contraction Cover organism and function in muscle contraction

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19 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-19 Phylum Cnidaria Cnidocytes Many cnidarians are effective predators Many cnidarians are effective predators Possible due to presence of a unique cell type, the cnidocyte Possible due to presence of a unique cell type, the cnidocyte Cnidoctyes Cnidoctyes Located in invaginations of ectodermal cells and some gastrodermal cells Located in invaginations of ectodermal cells and some gastrodermal cells Produces one of over 20 types of cnidae Produces one of over 20 types of cnidae One type of cnida is the nematocyst One type of cnida is the nematocyst

20 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-20 Phylum Cnidaria Nematocyts Nematocyts Tiny capsules made of chitin-like material and containing a coiled filament Tiny capsules made of chitin-like material and containing a coiled filament End of capsule is covered End of capsule is covered Filament may have tiny barbs or spines Filament may have tiny barbs or spines Except in Anthozoa, cnidocytes equipped with trigger-like cnidocil (modified cilium) Except in Anthozoa, cnidocytes equipped with trigger-like cnidocil (modified cilium) Tactile stimulation cause nematocyst to discharge Tactile stimulation cause nematocyst to discharge After Cnidae discharge, cnidocyte is absorbed and another develops After Cnidae discharge, cnidocyte is absorbed and another develops

21 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-21 Phylum Cnidaria Mechanism of Nematocyst Discharge Mechanism of Nematocyst Discharge When stimulated, water to rush into the capsule When stimulated, water to rush into the capsule The operculum opens and rapidly launches the filament The operculum opens and rapidly launches the filament Barbs inject poison into prey Barbs inject poison into prey Only a few jellyfish and the Portuguese man- of-war can seriously harm humans Only a few jellyfish and the Portuguese man- of-war can seriously harm humans

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24 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-24 Phylum Cnidaria Feeding and Digestion Polyps Polyps Typically carnivorous Typically carnivorous Catch prey with tentacles and pass them to the gastrovascular cavity Catch prey with tentacles and pass them to the gastrovascular cavity Gland cells discharge enzymes to begin extracellular digestion Gland cells discharge enzymes to begin extracellular digestion Intracellular digestion continues in the gastrodermis Intracellular digestion continues in the gastrodermis

25 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-25 Phylum Cnidaria Polyps in colonial hydrozoans Polyps in colonial hydrozoans Pass food into a common gastrovascular cavity Pass food into a common gastrovascular cavity Feeding and digestion in hydromedusae Feeding and digestion in hydromedusae Similar to that seen in the polyps Similar to that seen in the polyps Schyphomedusae Schyphomedusae Equipped with extended mouth edge (manubrium) Equipped with extended mouth edge (manubrium) Used in capturing and ingesting prey Used in capturing and ingesting prey Anthozoan polyps Anthozoan polyps Carnivorous Carnivorous Expand and stretch tentacles in search of prey Expand and stretch tentacles in search of prey Some small anthozoans Some small anthozoans Feed on minute forms captured by ciliary currents Feed on minute forms captured by ciliary currents Corals supplement their nutrition with carbon collected from algal symbionts Corals supplement their nutrition with carbon collected from algal symbionts

26 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-26 Phylum Cnidaria Nerve Net Nerve net of cnidarians one of the best examples of diffuse nervous system Nerve net of cnidarians one of the best examples of diffuse nervous system Two nerve nets, one at the base of epidermis and one at the base of gastrodermis, interconnect Two nerve nets, one at the base of epidermis and one at the base of gastrodermis, interconnect Nerve action potentials transmitted across synapses by neurotransmitters Nerve action potentials transmitted across synapses by neurotransmitters Unlike higher animals, Unlike higher animals, Nerve nets have neurotransmitters on both sides of the synapses Nerve nets have neurotransmitters on both sides of the synapses Allowing transmission in either direction Allowing transmission in either direction No myelin sheath on axons No myelin sheath on axons

27 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-27 Phylum Cnidaria Nerve cells synapse with both slender sensory cells and epitheliomuscular Nerve cells synapse with both slender sensory cells and epitheliomuscular Association often called a neuromuscular system Association often called a neuromuscular system The nerve net pattern is also found in annelid and human (nerve plexus) digestive systems The nerve net pattern is also found in annelid and human (nerve plexus) digestive systems

28 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-28 Phylum Cnidaria Class Hydrozoa Most marine and colonial with both polyp and medusa forms Most marine and colonial with both polyp and medusa forms Hydra is not typical Hydra is not typical Colonial Obelia is more exemplary Colonial Obelia is more exemplary Typical hydroid has a base, a stalk, and one or more terminal zooids (individual polyp animals) Typical hydroid has a base, a stalk, and one or more terminal zooids (individual polyp animals) Base is a rootlike stolon, or hydrorhiza Base is a rootlike stolon, or hydrorhiza Gives rise to stalks called hydrocauli Gives rise to stalks called hydrocauli Living part of the hydrocaulus is a tubular coenosarc Living part of the hydrocaulus is a tubular coenosarc Hydrocaulus covered by a non-living chitinous sheath, the perisarc Hydrocaulus covered by a non-living chitinous sheath, the perisarc

29 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-29 Phylum Cnidaria Individual zooids are attached to the hydrocaulus Individual zooids are attached to the hydrocaulus Hydranths (gastrozooids) are feeding polyps with circle of tentacles surrounding mouth Hydranths (gastrozooids) are feeding polyps with circle of tentacles surrounding mouth Hydranths may be thecate or athecate Hydranths may be thecate or athecate Colonial hydroids bud off new individuals Colonial hydroids bud off new individuals Individuals may be new hydranths or medusae buds Individuals may be new hydranths or medusae buds In Obelia, the medusae buds are formed by a reproductive polyp called a gonangium In Obelia, the medusae buds are formed by a reproductive polyp called a gonangium

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32 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-32 Phylum Cnidaria Hydroid medusae Hydroid medusae Usually smaller than schyphozoan medusae Usually smaller than schyphozoan medusae Margin of the bell projects inward as a shelf-like velum Margin of the bell projects inward as a shelf-like velum Mouth opens at the end of a suspended manubrium Mouth opens at the end of a suspended manubrium Mouth connects to a stomach and four radial canals Mouth connects to a stomach and four radial canals Radial canals connect to a ring canal that runs around the margin of the bell and connects with the hollow tentacles Radial canals connect to a ring canal that runs around the margin of the bell and connects with the hollow tentacles Bell margin has many sensory cells Bell margin has many sensory cells Typically also bears statocysts, specialized sense organs that function in equilibrium, and light-sensitive ocelli Typically also bears statocysts, specialized sense organs that function in equilibrium, and light-sensitive ocelli

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36 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-36 Phylum Cnidaria Freshwater Medusae Freshwater Medusae Craspedacusta Craspedacusta May have evolved from marine ancestors May have evolved from marine ancestors Found in Europe, the United States, and parts of Canada Found in Europe, the United States, and parts of Canada Craspedacusta medusae Craspedacusta medusae May reach a diameter of 20 mm May reach a diameter of 20 mm Polyps are tiny (2 mm) Polyps are tiny (2 mm) Polyp employs three methods of asexual reproduction Polyp employs three methods of asexual reproduction

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38 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-38 Phylum Cnidaria Hydra Hydra Found on the underside of aquatic leaves and lily pads in clean fresh water Found on the underside of aquatic leaves and lily pads in clean fresh water Worldwide distribution (16 species in North America) Worldwide distribution (16 species in North America) Body is a cylindrical tube Body is a cylindrical tube Aboral end has a basal or pedal disc for attachment Aboral end has a basal or pedal disc for attachment The mouth (oral end) on a conical elevation, the hypostome The mouth (oral end) on a conical elevation, the hypostome Ring of 6–10 hollow tentacles encircles mouth Ring of 6–10 hollow tentacles encircles mouth

39 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-39 Phylum Cnidaria The mouth opens to a gastrovascular cavity The mouth opens to a gastrovascular cavity Buds may project from the side, each develop a mouth and tentacles Buds may project from the side, each develop a mouth and tentacles Hydras feed on a variety of small crustaceans, insect larvae, and worms Hydras feed on a variety of small crustaceans, insect larvae, and worms Mouth is located on a raised hypostome, and opens into the gastrovascular cavity Mouth is located on a raised hypostome, and opens into the gastrovascular cavity Food organisms brush against the tentacles are captured by nematocysts Food organisms brush against the tentacles are captured by nematocysts

40 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-40 Phylum Cnidaria Organism moved by tentacles, and engulfed by the mouth Organism moved by tentacles, and engulfed by the mouth Opening of mouth activated by glutathione Opening of mouth activated by glutathione Inside gastrovascular cavity, gland cells discharge enzymes Inside gastrovascular cavity, gland cells discharge enzymes Myofibrils in nutritive-muscular cells run at right angles to the body axis, forms a weak circular muscle layer Myofibrils in nutritive-muscular cells run at right angles to the body axis, forms a weak circular muscle layer Water enters the gastrovascular cavity due to beating cilia Water enters the gastrovascular cavity due to beating cilia Water serves as a hydrostatic skeleton Water serves as a hydrostatic skeleton

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42 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-42 Phylum Cnidaria Epitheliomuscular cells Epitheliomuscular cells Form most of epidermis and cause muscular contraction Form most of epidermis and cause muscular contraction Undifferentiated interstitial cells Undifferentiated interstitial cells Develop into cnidoblasts, sex cells, buds, or nerve cells, but not epitheliomuscular cells. Gland cells Gland cells On the adhesive disc secrete an adhesive and sometimes a gas bubble for floating On the adhesive disc secrete an adhesive and sometimes a gas bubble for floating

43 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-43 Phylum Cnidaria Hydras have three types of cnidae Hydras have three types of cnidae Penetrants penetrate prey and inject poison Penetrants penetrate prey and inject poison Volvents recoil and entangle prey Volvents recoil and entangle prey Glutinants secrete an adhesive for locomotion and attachment Glutinants secrete an adhesive for locomotion and attachment Sensory cells among epidermal cells bear a flagellum for chemical and tactile stimuli and synapse with nerve cells Sensory cells among epidermal cells bear a flagellum for chemical and tactile stimuli and synapse with nerve cells Epidermal nerve cells are generally multipolar with both one-way and two-way synapses. Epidermal nerve cells are generally multipolar with both one-way and two-way synapses.

44 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-44 Phylum Cnidaria Hydras reproduce sexually and asexually Hydras reproduce sexually and asexually Asexual reproduction Asexual reproduction Budding Budding Most hydra are dioecious Most hydra are dioecious Temporary gonads appear in autumn, stimulated by lower temperatures or stagnation Temporary gonads appear in autumn, stimulated by lower temperatures or stagnation Eggs and sperm shed externally Eggs and sperm shed externally Zygotes undergo holoblastic cleavage to form hollow blastula Zygotes undergo holoblastic cleavage to form hollow blastula Cyst forms around embryo Cyst forms around embryo Encysted form endures the winter, then young hydras hatch in the spring Encysted form endures the winter, then young hydras hatch in the spring

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46 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-46 Phylum Cnidaria Other Hydrozoans Other Hydrozoans Orders Siphonophora and Chondrophora form polymorphic swimming or floating colonies Orders Siphonophora and Chondrophora form polymorphic swimming or floating colonies Contain several types of polyp individuals Contain several types of polyp individuals Dactylozooids are Dactylozooids are Fishing tentacles that sting prey and lift them to feeding polyps Fishing tentacles that sting prey and lift them to feeding polyps Gonophores Gonophores Sacs containing ovaries or testes. Sacs containing ovaries or testes. In Physalia, the float, pneumatophore In Physalia, the float, pneumatophore Thought to have expanded from the original larval polyp Thought to have expanded from the original larval polyp Other hydrozoans secrete calcareous skeletons resembling true corals and are the hydrocorals Other hydrozoans secrete calcareous skeletons resembling true corals and are the hydrocorals

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49 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-49 Phylum Cnidaria Class Scyphozoa Most of the larger jellyfishes belong to this class Most of the larger jellyfishes belong to this class Nearly all float in open sea Nearly all float in open sea One order is sessile, attached to seaweeds by a stalk One order is sessile, attached to seaweeds by a stalk Bells vary in shape and size Bells vary in shape and size Composed mostly of mesoglea Composed mostly of mesoglea Mesoglea contains ameboid cells and fibers Mesoglea contains ameboid cells and fibers Lack shelf-like velum found in hydrozoan medusae Lack shelf-like velum found in hydrozoan medusae Margin of the umbrella has indentations, each bearing a pair of lappets Margin of the umbrella has indentations, each bearing a pair of lappets

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52 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-52 Phylum Cnidaria Phylum Cnidaria Between lappets is a equilibrium sense organ Between lappets is a equilibrium sense organ Rhopalium Rhopalium Contains a hollow statocyst Contains a hollow statocyst Mouth located beneath the umbrella Mouth located beneath the umbrella Manubrium forms four oral arms Manubrium forms four oral arms Capture and ingest prey Capture and ingest prey Tentacles, manubrium, and often entire body may have nematocysts Tentacles, manubrium, and often entire body may have nematocysts

53 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-53 Phylum Cnidaria The nervous system consists of a nerve net The nervous system consists of a nerve net Sexes are separate Sexes are separate Fertilization is internal in the gastric pouch of the female Fertilization is internal in the gastric pouch of the female Zygote develops into a ciliated planula larva Zygote develops into a ciliated planula larva Attaches and develops into a scyphistoma Attaches and develops into a scyphistoma Scyphistoma undergoes strobilation Scyphistoma undergoes strobilation Form buds called ephyrae that break loose to form jellyfish medusae Form buds called ephyrae that break loose to form jellyfish medusae

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55 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-55 Phylum Cnidaria Class Staurozoa Commonly called stauromedusans Commonly called stauromedusans No medusa stage No medusa stage Solitary polyp body that is stalked Solitary polyp body that is stalked Uses adhesive disk to attach to seaweeds, and objects on sea bottom Uses adhesive disk to attach to seaweeds, and objects on sea bottom Polyp top resembles a medusa with eight extensions (“arms”) ending in tentacle clusters surrounding mouth Polyp top resembles a medusa with eight extensions (“arms”) ending in tentacle clusters surrounding mouth Reproduce sexually Reproduce sexually

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57 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-57 Phylum Cnidaria Class Cubozoa Medusa form is dominant Medusa form is dominant Polyp is inconspicuous or unknown Polyp is inconspicuous or unknown Umbrella is square Umbrella is square One or more tentacles extend from each corner One or more tentacles extend from each corner At base of each tentacle is a flat blade called a pedalium At base of each tentacle is a flat blade called a pedalium Umbrella edge turns inward to form a velarium Umbrella edge turns inward to form a velarium Increases swimming efficiency Increases swimming efficiency

58 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-58 Phylum Cnidaria Strong swimmers Strong swimmers Feed mostly on fish in nearshore areas Feed mostly on fish in nearshore areas Polyp stage is tiny Polyp stage is tiny New polyps bud laterally New polyps bud laterally Do not produce ephyrae but directly change into medusae Do not produce ephyrae but directly change into medusae The sea wasp The sea wasp Potentially fatal cubomedusan from Australia Potentially fatal cubomedusan from Australia

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60 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-60 Phylum Cnidaria Class Anthozoa Lack a medusa stage Lack a medusa stage All marine, in both deep and shallow water, and vary in size All marine, in both deep and shallow water, and vary in size Three subclasses: Zoantharia, Cerianthpatharia, and Alcyonaria Three subclasses: Zoantharia, Cerianthpatharia, and Alcyonaria Zoantharia and Cerianthpatharia are hexamerous; Alcyonaria are octomerous Zoantharia and Cerianthpatharia are hexamerous; Alcyonaria are octomerous Gastrovascular Cavity Gastrovascular Cavity Large and partitioned by septa or mesenteries, inward extensions of body wall Large and partitioned by septa or mesenteries, inward extensions of body wall Septa may be coupled or paired Septa may be coupled or paired

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64 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-64 Phylum Cnidaria The mesoglea is mesenchyme containing ameboid cells The mesoglea is mesenchyme containing ameboid cells No special organs for respiration or excretion No special organs for respiration or excretion Sea Anemones Polyps larger and heavier than hydrozoan polyps Polyps larger and heavier than hydrozoan polyps Attach to shells, rocks, timber, etc. by pedal discs Attach to shells, rocks, timber, etc. by pedal discs

65 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-65 Phylum Cnidaria Some burrow in mud or sand Some burrow in mud or sand Crown of tentacles surrounds the flat oral disc Crown of tentacles surrounds the flat oral disc Slit-shaped mouth leads into a pharynx Slit-shaped mouth leads into a pharynx Siphonoglyph (ciliated groove) creates a water current directed into the pharynx Siphonoglyph (ciliated groove) creates a water current directed into the pharynx Transports oxygen, removes wastes, and maintains fluid pressure for a hydrostatic skeleton Transports oxygen, removes wastes, and maintains fluid pressure for a hydrostatic skeleton

66 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-66 Phylum Cnidaria Gastrovascular cavity divided into six pairs of primary septa or mesenteries Gastrovascular cavity divided into six pairs of primary septa or mesenteries Smaller incomplete septa subdivide the large chambers increasing surface area Smaller incomplete septa subdivide the large chambers increasing surface area Free edge of each incomplete septum Free edge of each incomplete septum Forms a septal filament with nematocysts and gland cells for digestion Forms a septal filament with nematocysts and gland cells for digestion Acontia threads at lower ends of septal filaments Acontia threads at lower ends of septal filaments Equipped with nematocysts Equipped with nematocysts May protrude through mouth to help secure prey May protrude through mouth to help secure prey

67 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-67 Phylum Cnidaria When in danger, water rapidly expelled through pores as the anemone contracts to a small size When in danger, water rapidly expelled through pores as the anemone contracts to a small size Feeding behavior under chemical control Feeding behavior under chemical control Asparagine activates feeding causing tentacles to bend toward the mouth Asparagine activates feeding causing tentacles to bend toward the mouth Reduced glutathione induces swallowing Reduced glutathione induces swallowing Longitudinal muscles of the epidermis Longitudinal muscles of the epidermis Only occur in the tentacles and oral disc Only occur in the tentacles and oral disc Longitudinal muscles of the column Longitudinal muscles of the column Gastrodermal and located in the septa Gastrodermal and located in the septa Most anemones can glide slowly on pedal discs Most anemones can glide slowly on pedal discs Some can swim with limited ability Some can swim with limited ability

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69 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-69 Phylum Cnidaria When in danger, they contract and withdraw tentacles and oral discs When in danger, they contract and withdraw tentacles and oral discs Most harbor symbiotic algae Most harbor symbiotic algae Some have a mutualistic relationship with hermit crabs Some have a mutualistic relationship with hermit crabs

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71 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-71 Phylum Cnidaria Reproduction Reproduction Some dioecious, some monoecious Some dioecious, some monoecious Monoecious species are protandrous Monoecious species are protandrous Produce sperm first and eggs later Produce sperm first and eggs later Gonads on margins of septa Gonads on margins of septa Fertilization is external or in gastrovascular cavity Fertilization is external or in gastrovascular cavity Zygote becomes a ciliated larva Zygote becomes a ciliated larva Pedal laceration, small pieces of pedal disc break off and regenerate a small anemone Pedal laceration, small pieces of pedal disc break off and regenerate a small anemone Longitudinal and transverse fission, and budding occur Longitudinal and transverse fission, and budding occur

72 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-72 Phylum Cnidaria Hexacorallian Corals Members of the order Scleractinia Members of the order Scleractinia Also called true or stony corals Also called true or stony corals Described as miniature sea anemones that live in calcareous cups they have secreted Described as miniature sea anemones that live in calcareous cups they have secreted Gastrovascular cavity is hexamerous Gastrovascular cavity is hexamerous No siphonoglyph No siphonoglyph No pedal disc No pedal disc Secrete a limey skeletal cup with sclerosepta projecting up into the polyp Secrete a limey skeletal cup with sclerosepta projecting up into the polyp Sheet of living tissue forms over the coral surface Sheet of living tissue forms over the coral surface Connects all gastrovascular cavities Connects all gastrovascular cavities

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75 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-75

76 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-76 Phylum Cnidaria Tube Anemones and Thorny Corals Tube Anemones and Thorny Corals Members of subclass Ceriantipatharia Members of subclass Ceriantipatharia Have coupled but unpaired septa. Have coupled but unpaired septa. Tube anemones Tube anemones Solitary and live in soft sediments Solitary and live in soft sediments Thorny or black corals Thorny or black corals Colonial and attach to firm substrata Colonial and attach to firm substrata Both groups have few species and live in warmer seas Both groups have few species and live in warmer seas

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78 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-78

79 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-79 Phylum Cnidaria Alcyonarian (Octocorallian) Corals Octomerous symmetry, Octomerous symmetry, Eight pinnate tentacles Eight pinnate tentacles Eight unpaired complete septa Eight unpaired complete septa All are colonial All are colonial Gastrovascular cavities communicate through tubes called solenia Gastrovascular cavities communicate through tubes called solenia Solenia pass through an extensive mesoglea Solenia pass through an extensive mesoglea Show great variation in form of colony Show great variation in form of colony

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83 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-83 Phylum Cnidaria Coral Reefs Coral Reefs Great diversity of organisms Great diversity of organisms Rivaled only by tropical rainforests Rivaled only by tropical rainforests Plants and animals are limited to top layer Plants and animals are limited to top layer Above the calcium carbonate deposits Above the calcium carbonate deposits Hermatypic corals and coralline algae form most coral reefs Hermatypic corals and coralline algae form most coral reefs Require warmth, light, and salinity of undiluted sea water Require warmth, light, and salinity of undiluted sea water Limited to shallow waters between 30 degrees north and 30 degrees south latitude Limited to shallow waters between 30 degrees north and 30 degrees south latitude Photosynthetic zooxanthellae live in their tissues Photosynthetic zooxanthellae live in their tissues Provide food for corals and recycle phosphorus and nitrogenous wastes Provide food for corals and recycle phosphorus and nitrogenous wastes

84 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-84 Phylum Cnidaria Types of Reefs Types of Reefs Fringing Reef Fringing Reef Near the land with no lagoon or a very narrow lagoon Near the land with no lagoon or a very narrow lagoon Barrier Reef Barrier Reef Parallel to shore with a wide and deep lagoon Parallel to shore with a wide and deep lagoon Atolls Atolls Encircle a lagoon but not an island Encircle a lagoon but not an island Have a steep bank on the seaward slope Have a steep bank on the seaward slope Patch or Bank Reefs Patch or Bank Reefs Some distance back from any steep slopes Some distance back from any steep slopes

85 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-85 Phylum Cnidaria Reef front or fore reef slope Reef front or fore reef slope Side facing the sea Side facing the sea Reef crest Reef crest Shallow water or emergent at top of the reef front Shallow water or emergent at top of the reef front Wave action breaks pieces off Wave action breaks pieces off Reef flat toward the shore receives debris and coralline sand Reef flat toward the shore receives debris and coralline sand Support a diversity of corals and fish Support a diversity of corals and fish Few nutrients enter or leave the system Few nutrients enter or leave the system Little is lost efficiency in recycling among interacting organisms Little is lost efficiency in recycling among interacting organisms

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87 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-87 Phylum Cnidaria Nutrients from fertilizer and sewage threaten coral reefs with excessive algal growth Nutrients from fertilizer and sewage threaten coral reefs with excessive algal growth Persian Gulf reefs have withstood surprising amounts of oil pollution Persian Gulf reefs have withstood surprising amounts of oil pollution Coral reefs in many areas are threatened by factors mostly of human origin Coral reefs in many areas are threatened by factors mostly of human origin Higher atmospheric concentrations of carbon dioxide (from burning hydrocarbon fuels) tends to acidify ocean water, which makes precipitation of CaCO 3 by corals more difficult metabolically Higher atmospheric concentrations of carbon dioxide (from burning hydrocarbon fuels) tends to acidify ocean water, which makes precipitation of CaCO 3 by corals more difficult metabolically

88 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-88 Phylum Cnidaria Classification of Cnidaria Class Hydrozoa Class Hydrozoa Class Scyphozoa Class Scyphozoa Class Staurozoa Class Staurozoa Class Cubozoa Class Cubozoa Class Anthozoa Class Anthozoa Subclass Hexacorallia (Zoantharia) Subclass Hexacorallia (Zoantharia) Subclass Ceriantipatharia Subclass Ceriantipatharia Subclass Octocorrallia (Alcyonaria) Subclass Octocorrallia (Alcyonaria)

89 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-89 Phylum Ctenophora Phylum composed of about 150 species Phylum composed of about 150 species All marine, most prefer warm waters All marine, most prefer warm waters Ctenophores Ctenophores Eight rows of comb-like plates used for locomotion Eight rows of comb-like plates used for locomotion Nearly all free-swimming, few creep or are sessile Nearly all free-swimming, few creep or are sessile Body structure (ellipsoid or spherical shape) Body structure (ellipsoid or spherical shape) Biradial symmetry due to presence of two tentacles. Biradial symmetry due to presence of two tentacles. Oral-aboral axis, no head Oral-aboral axis, no head Translucent body with a gelatinous layer that contains muscle fibers (fibers are radial, meridional, and latitudinal bands) Translucent body with a gelatinous layer that contains muscle fibers (fibers are radial, meridional, and latitudinal bands)

90 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-90 Phylum Ctenophora Complete gut Complete gut Acoelomate Acoelomate Feeding Habits Feeding Habits Trailing tentacles capture planktonic organisms by means of epidermal glue cells called colloblasts Trailing tentacles capture planktonic organisms by means of epidermal glue cells called colloblasts Short tentacles collect food on the ciliated body surface Short tentacles collect food on the ciliated body surface Ctenophores without tentacles feed on other gelatinous animals Ctenophores without tentacles feed on other gelatinous animals Structuring classes within the Ctenophores still being developed Structuring classes within the Ctenophores still being developed

91 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-91 Phylum Ctenophora Representative Type: Pleurobrachia Transparent and 1.5–2 cm in diameter Transparent and 1.5–2 cm in diameter Oral pole bears the mouth opening Oral pole bears the mouth opening Aboral pole equipped with statocyst Aboral pole equipped with statocyst Eight equally-spaced bands called comb rows extend from aboral to oral pole Eight equally-spaced bands called comb rows extend from aboral to oral pole Each band made of transverse plates of long fused cilia called comb plates Each band made of transverse plates of long fused cilia called comb plates Beat in each row begins at the aboral end and moves along combs to the oral end Beat in each row begins at the aboral end and moves along combs to the oral end All eight rows beat in unison All eight rows beat in unison Drives the animal forward mouth-first Drives the animal forward mouth-first

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94 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-94 Tentacles Tentacles Two tentacles are long, solid and extensible Two tentacles are long, solid and extensible Retract into a pair of tentacle sheaths Retract into a pair of tentacle sheaths Surface bears colloblasts or glue cells that secrete sticky material to hold animals Surface bears colloblasts or glue cells that secrete sticky material to hold animals Body wall resembles cnidarians with a gelatinous collenchyme in the interior Body wall resembles cnidarians with a gelatinous collenchyme in the interior Muscle cells are distinct and not part of the epitheliomuscular cells Muscle cells are distinct and not part of the epitheliomuscular cells Phylum Ctenophora

95 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-95 Digestion and Feeding Digestion and Feeding Gastrovascular system comprises a mouth, pharynx, stomach and canals that run to the comb plates, tentacular sheaths, and elsewhere Gastrovascular system comprises a mouth, pharynx, stomach and canals that run to the comb plates, tentacular sheaths, and elsewhere Two blind canals terminate near mouth Two blind canals terminate near mouth Aboral canal divides into two small anal canals that expel wastes Aboral canal divides into two small anal canals that expel wastes Digestion both extracellular and intracellular Digestion both extracellular and intracellular Phylum Ctenophora

96 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-96 Phylum Ctenophora Respiration and excretion occur through body surface Respiration and excretion occur through body surface Nervous and Sensory Systems Nervous and Sensory Systems Resembles cnidarians Resembles cnidarians Subepidermal plexus concentrated under each comb plate Subepidermal plexus concentrated under each comb plate Statocyst is a bell-like chamber Statocyst is a bell-like chamber Tufts of cilia sense changes in pressure from statolith as animal changes position Tufts of cilia sense changes in pressure from statolith as animal changes position Epidermis bears sensory cells sensitive to chemical and other stimuli Epidermis bears sensory cells sensitive to chemical and other stimuli

97 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-97 Phylum Ctenophora When ctenophore contacts an unfavorable stimulus When ctenophore contacts an unfavorable stimulus Cilia reverse their beat Cilia reverse their beat Moves organisms backward Moves organisms backward Comb plates are sensitive to touch Comb plates are sensitive to touch Withdraw into the animal when touched Withdraw into the animal when touched

98 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-98 Phylum Ctenophora Reproduction and Development Reproduction and Development Monoecious Monoecious Fertilized eggs discharged through epidermis into water Fertilized eggs discharged through epidermis into water Cleavage is determinate Cleavage is determinate Free-swimming cydippid larva somewhat resembles adult Free-swimming cydippid larva somewhat resembles adult Some consider cellular nature of mesoglea to constitute a mesoderm Some consider cellular nature of mesoglea to constitute a mesoderm If mesoderm is derived from endoderm, both ctenophores and cnidarians are diploblastic If mesoderm is derived from endoderm, both ctenophores and cnidarians are diploblastic

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100 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-100 Phylum Ctenophora Other Ctenophores Beroe Beroe Large conical ctenophore that lacks tentacles Large conical ctenophore that lacks tentacles Venus’ girdle Venus’ girdle Band-like ctenophore over one meter long Band-like ctenophore over one meter long Ctenoplana Ctenoplana flattened ctenophores that creep rather than swim flattened ctenophores that creep rather than swim Most ctenophores are bioluminescent at night Most ctenophores are bioluminescent at night

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102 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-102 Phylogeny and Adaptive Diversification Phylogeny of the Diploblasts Phylogeny of the Diploblasts Distinctions between diploblastic and tripoblastic conditions blurred Distinctions between diploblastic and tripoblastic conditions blurred Due to recent detailed morphological studies and studies in gene expressions Due to recent detailed morphological studies and studies in gene expressions Ctenophores and cnidarians have typical diploblastic characteristics Ctenophores and cnidarians have typical diploblastic characteristics Gelatinous middle surrounded by outer epidermal layer derived from ectoderm Gelatinous middle surrounded by outer epidermal layer derived from ectoderm Inner gut lining derived from endoderm Inner gut lining derived from endoderm However, the cells of the gelatinous layer are problematic However, the cells of the gelatinous layer are problematic

103 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-103 Phylogeny and Adaptive Diversification If derived from endoderm If derived from endoderm Organisms are characteristic of triploblasts Organisms are characteristic of triploblasts But these cells may be derived from ectoderm But these cells may be derived from ectoderm Some refer to this layer as ectomesoderm Some refer to this layer as ectomesoderm Most cnidarians have few cells with the mesoglea, so little debate whether they are diploblastic Most cnidarians have few cells with the mesoglea, so little debate whether they are diploblastic

104 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-104 However, during hydrozoan medusae stage However, during hydrozoan medusae stage Development of the entocodon layer has led to the suggestion that cnidarians are triploblastic Development of the entocodon layer has led to the suggestion that cnidarians are triploblastic One product of the entocodon is striated muscle One product of the entocodon is striated muscle Unlike contractile epitheliomuscular cells of other cnidarians Unlike contractile epitheliomuscular cells of other cnidarians Smooth and striated muscles are true muscle cells Smooth and striated muscles are true muscle cells In triploblasts, true muscles are produced by mesodermal cells In triploblasts, true muscles are produced by mesodermal cells Hydrozoans entocodon is ectodermal in origin Hydrozoans entocodon is ectodermal in origin Other smooth muscle cells present in hydrozoan medusae are of ectodermal origin Other smooth muscle cells present in hydrozoan medusae are of ectodermal origin Phylogeny and Adaptive Diversification

105 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-105 Phylogeny and Adaptive Diversification Probes of gene expression show that homologous gene expression is occurring in those of triploblast mesoderm and diploblast mesoderm. Probes of gene expression show that homologous gene expression is occurring in those of triploblast mesoderm and diploblast mesoderm. Intepretation of these probes is not complete Intepretation of these probes is not complete May represent independent origin of muscle in one branch of the diploblastic lineage May represent independent origin of muscle in one branch of the diploblastic lineage

106 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-106 Recent re-examination of the development of ctenophores has led to the observation that muscle cells in the middle layer originate from endodermal cells Recent re-examination of the development of ctenophores has led to the observation that muscle cells in the middle layer originate from endodermal cells If this is confirmed If this is confirmed Ctenophores are triploblastic along with bilaterally symmetrical animals. Ctenophores are triploblastic along with bilaterally symmetrical animals. Phylogeny and Adaptive Diversification

107 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-107 Phylogeny and Adaptive Diversification Body symmetry also debated Body symmetry also debated Although adult ctenophore is radially symmetrical Although adult ctenophore is radially symmetrical Cnidarian planula larva swims with one end moving forward Cnidarian planula larva swims with one end moving forward This end could be designated as anterior end giving the planula a distinct anterior-posterior axis This end could be designated as anterior end giving the planula a distinct anterior-posterior axis The question remains: Did the radially symmetrical cnidarians have a bilaterally symmetrical ancestor or does the genetic potential for bilateral symmetry predate the bilateral body plan? The question remains: Did the radially symmetrical cnidarians have a bilaterally symmetrical ancestor or does the genetic potential for bilateral symmetry predate the bilateral body plan?

108 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-108 Given the yet unanswered questions to origins of development Given the yet unanswered questions to origins of development Branching order for the diploblastic phyla is not yet determined Branching order for the diploblastic phyla is not yet determined We predict a polytomy for cnidarian, ctenophoran, and placozoan branches We predict a polytomy for cnidarian, ctenophoran, and placozoan branches Phylogeny and Adaptive Diversification

109 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-109 Adaptive Diversification Adaptive Diversification Neither phylum has deviated far from basic structural plan Neither phylum has deviated far from basic structural plan Cnidarians Cnidarians Achieved large numbers of individuals and species Achieved large numbers of individuals and species Demonstrate large diversity considering the simplicity of body plan Demonstrate large diversity considering the simplicity of body plan Efficient predators Efficient predators Some feeding on prey larger than themselves Some feeding on prey larger than themselves Some feeding on small particles Some feeding on small particles Some colonial forms grow to great size among corals Some colonial forms grow to great size among corals Others show polymorphism and specialization of individuals within a colony Others show polymorphism and specialization of individuals within a colony Phylogeny and Adaptive Diversification

110 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-110 Ctenophores Ctenophores Adhere to the arrangement of comb plates and biradial symmetry Adhere to the arrangement of comb plates and biradial symmetry Vary in body shape and presence or absence of tentacles Vary in body shape and presence or absence of tentacles Phylogeny and Adaptive Diversification

111 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13-111 Cnidarian Phylogeny Cnidarian Phylogeny Relationships among cnidarian classes are still controversial: Relationships among cnidarian classes are still controversial: Which came first, the polyp or the medusa? One hypothesis postulates that the basal cnidarian was a trachyline-like hydrozoan with a medusa stage. One hypothesis postulates that the basal cnidarian was a trachyline-like hydrozoan with a medusa stage. Another hypothesis suggests that the basal cnidarian was an anthozoan polyp without a medusa in the life cycle. Another hypothesis suggests that the basal cnidarian was an anthozoan polyp without a medusa in the life cycle. Phylogeny and Adaptive Diversification


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