Coelomate Invertebrates Chapter 34

Introduction Coelomates have a body design that: 1. Repositions the body’s fluid 2. Allows complex tissues/organs to develop 3. Allows for a larger body size Coeloms evolved multiple times during animal evolution

Phylum Mollusca Mollusks are second in diversity only to arthropods -Exhibit a wide variety of sizes and body forms -Live in many different environments -Include snails, slugs, clams, octopuses and others

Phylum Mollusca

Phylum Mollusca (Cont.)

Phylum Mollusca Mollusks evolved in the oceans and most groups have remained there They are an important source of human food They are economically significant in other ways -Pearls are produced in oysters -Mother-of-pearl is produced in the shells of abalone Mollusks can also be pests -Zebra mussel (Dreissena polymorpha)

Mollusk Body Plan Mollusks are bilaterally symmetrical -Characterized by a reduced coelom surrounding the heart and excretory organs The digestive, excretory and reproductive organs are concentrated in a visceral mass Mollusks may have a differentiated head at the anterior end of the body

Mollusk Body Plan Mantle = A thick epidermis that covers the dorsal side of the body -Forms a cavity which houses the respiratory organs (ctenidia, or gills) and the openings of excretory, reproductive & digestive organs The muscular foot of a mollusk is adapted for locomotion, attachment, food capture -Or a combination of the above

Mollusk Body Plan

Mollusk Body Plan (Cont.)

Mollusk Body Plan Most mollusks produce an external calcium carbonate-rich shell -Used for protection -Some species have internalized or reduced shells Most mollusks have a rasping tongue-like organ called the radula -Used for feeding

Mollusk Body Plan

Mollusk Body Plan Nephridia = Special excretory structures that remove nitrogenous wastes -Consist of cilia-lined openings called nephrostomes Except for cephalopods, all mollusks have an open circulatory system Cephalopods have a closed circulatory system

Mollusk Reproduction Most mollusks have distinct male and female individuals Most engage in external fertilization In marine mollusks, embryos develop through spiral cleavage -Trochophores: Free-swimming larval stage -Veliger: Second free-swimming larval stage -Only in bivalves and snails

Mollusk Reproduction

Classes of Mollusks There are eight recognized classes -Four are representatives of the phylum 1. Polyplacophora 2. Gastropoda 3. Bivalvia 4. Cephalopoda

Classes of Mollusks Class Polyplacophora (Chitons) -Marine mollusks that have oval bodies with eight overlapping dorsal calcareous plates -Body is not segmented under the plates -Most chitons are grazing herbivores

Classes of Mollusks Class Gastropoda (Snails and slugs) -A primarily marine group -Heads typically have pairs of tentacles with eyes at the ends -During embryological development, gastropods undergo 1. Torsion – Mantle cavity and anus are moved from the posterior to the front 2. Coiling – Spiral winding of the shell

Classes of Mollusks

Classes of Mollusks Class Bivalvia (Bivalves) -Includes clams, scallops, mussels, oysters and others -Have two lateral (right and left) shells (valves) hinged together dorsally -Most are sessile filter-feeders -Water circulation is mediated by siphons and rhythmic beating of cilia on gills

Classes of Mollusks

Classes of Mollusks Class Cephalopoda -Active marine predators -Foot has evolved into a series of arms equipped with suction cups -Squids have 10; octopuses, 8; and nautiluses, 80 to 90 -Have highly developed nervous systems -Exhibit complex patterns of behavior and a high level of intelligence

Classes of Mollusks

Classes of Mollusks Class Cephalopoda -Many have an ink sac and are capable of expelling ink to confuse predators -Octopuses and squids can change color using pouches of pigment called chromatophores

Phylum Annelida Annelid worms exhibit segmentation (building of body from repeated units) -Allows for specialization Members of this phylum are not monophyletic

Phylum Annelida An annelid consists of a series of ring-like elements running the length of the body -Divided internally by septa The anterior (front) segments contain specialized sensory organs A ventral nerve cord connects the ganglia in each segment with each other and the brain

Phylum Annelida

Phylum Annelida Annelids move using their hydrostatic skeleton -Each segment contains chitin bristles (chaetae) that help anchor the worms Most have a closed circulatory system They exchange O2 and CO2 through their body surfaces Excretory system consists of a pair of ciliated, funnel-shaped nephridia per segment

Phylum Annelida Annelids have traditionally been classified into three classes: 1. Class Polychaeta 2. Class Oligochaeta 3. Class Hirudinea Hirudinea is now considered a sub-class of Oligochaeta

Phylum Annelida Class Polychaeta (Polychaetes) -Mostly marine worms, such as tubeworms -Unusual forms and iridescent colors -Have a differentiated head -Have paired parapodia on most segments -Used in swimming, burrowing, crawling -Sexes are usually separate -Typically lack permanent gonads

Phylum Annelida

Phylum Annelida Class Oligochaeta (Earthworms and leeches) -Mostly terrestrial Earthworms -Consist of 100-175 segments, with a mouth on the first and an anus on the last -Lack eyes, parapodia and head -Have fewer setae than polychaetes

Phylum Annelida Earthworms are hermaphroditic -Clitellum secretes mucus that holds the worms together during copulation -Also secretes a mucus cocoon, in which the fertilized egg develops

Phylum Annelida Leeches -Occur mostly in freshwater -Usually flattened dorsoventrally -Cross-fertilization is obligatory -Have no chaetae (except for one species) -Medicinal leech, Hirudo medicinalis -Secretes anticoagulant

The Lophophorates Include two phyla of mostly marine animals: Bryozoa and Brachiopoda Both convergently evolved a lophophore -A circular or U-shaped ridge around the mouth with 1-2 rows of ciliated tentacles -Functions in gas exchange and feeding Most members undergo radial cleavage

Phylum Bryozoa Bryozoans are small and live in colonies -Their anus opens near their mouth -Phylum also called Ectoprocta -Individuals secrete a tiny chitinous chamber called a zoecium -Used for attachment -Asexual reproduction occurs frequently by budding

Phylum Bryozoa

Phylum Bryozoa (Cont.)

Phylum Brachiopoda Brachiopods have two calcified shells -Valves are dorsal and ventral (not lateral as in bivalves) -Solitary lophophorates Phoronids were once a separate phylum -Each individual secretes a chitinous tube and lives out its life within it -Develop as protostomes (unlike brachiopods)

Phylum Arthropoda Arthropods are the most successful animals -1,000,000 species (2/3rd of all species) -About 80% are insects -For each human, 200 million insects are alive at any one time Athropods affect all aspects of human life Are divided into four major classes: -Arachnids, myriapods, crustaceans and insects

Arthropod Morphology All arthropods have jointed appendages -Modifications: antennae, mouthparts, legs Arthropods also have an exoskeleton made of secreted chitin and protein -Functions: protection & muscle attachment -Its thickness limits arthropod body size Arthropod bodies are segmented -Some segments are specialized into functional groups, or tagmata

Arthropod Morphology

Arthropod Morphology Arthropods have an open circulatory system Compound eyes are found in many arthropods -Composed of independent visual units called ommatidia Other arthropods have simple eyes, or ocelli -Have single lenses -Distinguish light from darkness

Arthropod Morphology

Arthropod Morphology Nervous system consists of a double chain of segmented ganglia on ventral surface -Brain seems to be an inhibitor, rather than as a stimulator, as it is in vertebrates Respiratory system consists of tracheae and tracheoles -Connected to the exterior by spiracles

Arthropod Morphology

Arthropod Morphology Arthropods have a unique excretory system consisting of Malpighian tubules -Eliminates nitrogenous wastes as concentrated uric acid or guanine Arthropods periodically undergo ecdysis or molting -Shedding the outer cuticular layer

Arthropod Morphology

Class Arachnida Arachnids are largely terrestrial organisms -Spiders, ticks, mites, scorpions, and others The most anterior appendages, chelicerae, often function as fangs or pincers Body is divided into two main tagmata -Prosoma (anterior): Bears all appendages -Opisthosoma (posterior): Contains the reproductive organs

Class Arachnida Pedipalps (palps) are posterior to chelicerae -Resemble legs, but have one less segment -Used as copulatory organs, pincers, or sensors Most arachnids are carnivorous -Mites are largely herbivorous

Class Arachnida Order Araneae (spiders) -About 35,000 species -Many spiders catch their prey in silk webs -Silk protein forced out of spinnerets found on the posterior of the abdomen -Other spiders actively hunt their prey -All spiders have poison glands leading through their chelicerae

Class Arachnida

Class Arachnida Order Acari (mites and ticks) -Largest and most diverse arachnid order -Most mites are small -Cephalothorax and abdomen are fused into an unsegmented ovoid body -Ticks are larger than mites -Are blood-eating parasites -Can carry many diseases (spotted fevers, Lyme disease)

Centipedes and Millipedes Centipedes (class Chilopoda) and Millipedes (class Diplopoda) have bodies with a head followed by numerous segments Centipedes are all carnivores (eat insects) Millipedes are largely herbivores In both fertilization is internal -The sexes are separate

Centipedes and Millipedes Centipedes have fewer legs than millipedes -Centipedes: one leg pair on each segment -Millipedes: two on some or all segments

Class Crustacea Crustaceans are primarily aquatic organisms -Crabs, shrimps, lobsters, barnacles, others Have three tagmata -The two most anterior fuse to form a cephalothorax Have two pairs of antennae, three pairs of appendages, and various pairs of legs Most appendages are biramous

Class Crustacea Mandibles (biting jaws) likely evolved from a pair of limbs that took on a chewing function Most crustaceans have separate sexes Majority develop through a nauplius stage

Class Crustacea Decapod crustaceans include shrimps, lobsters, crabs and crayfish -Have ten feet -Exoskeleton usually enforced with CaCO3 -Most body segments are fused into a cephalothorax -Lobsters and crayfish have appendages that aid in swimming -Swimmerets and uropods

Class Crustacea

Class Crustacea Order Cirripedia -Barnacles are crustaceans that are sessile as adults -Free-swimming larvae -Are hermaphroditic -Some have stalks

Class Hexapoda Insects are by far the largest group of animals -More than half of all named animal species Insects are primarily a terrestrial group Approximately one billion billion (1018) insects are alive at any one time

Class Hexapoda

Class Hexapoda (Cont.)

Class Hexapoda (Cont.)

Class Hexapoda External features -Three body regions 1. Head = Has pair of antennae and modified mouthparts 2. Thorax = Has three segments, each with a pair of legs -May have one or two pairs of wings 3. Abdomen Most insects have compound eyes

Class Hexapoda

Class Hexapoda Internal organization -The digestive tract is a coiled tube -Lined with cuticle on anterior and posterior regions -Digestion takes place in stomach (midgut) -Excretion tales place through Malpighian tubules -Tracheae permeate all tissues

Class Hexapoda Sensory receptors -Sensory setae are hair-like structures -Detect chemical and mechanical signals -Tympanal organs are composed of a thin membrane, the tympanum -Detect sound -In addition, insects can communicate by means of pheromones

Class Hexapoda Insect life histories -Many insects undergo metamorphosis -Simple metamorphosis (grasshopers) -Immature stages similar to adults -Complete metamorphosis (butterflies) -Immature larva are wormlike -A resting stage, pupa or chrysalis, precedes the final molt into adult form

Phylum Echinodermata Echinoderms are an ancient group of marine animals, with about 6000 living species -Characterized by deuterostome development and an endoskeleton

Echinoderm Body Plan The echinoderm body plan undergoes a fundamental shift during development -Larvae = bilateral symmetry -Adults = pentaradial symmetry Body structure is discussed in reference to their mouths, which define the oral surface

Echinoderm Body Plan Endoskeleton -Found internal to a delicate epidermis which contains thousands of neurosensory cells -Composed of either movable or fixed calcium-rich (calcite) plates called ossicles -Perforated by pores to allow extension of tube feet -Contains mutable collagenous tissue -Provides ability to autotomize body parts

Echinoderm Body Plan Water-vascular system -A hydraulic system that aids in movement and feeding -Composed of a central ring canal from which five radial canals extend into each of the body’s five parts -Madreporite = Opening for water entry -Ampulla = Muscular sac for tube feet control

Echinoderm Body Plan

Echinoderm Body Plan Echinoderms have a large coelom which connects with a complicated tub system -Helps provide circulation and respiration through extensions called papulae

Echinoderm Body Plan Reproduction -In some echinoderms, asexual reproduction takes place by splitting -Broken parts can regenerate the whole animal -Most reproduction in the phylum is sexual and external

Classes of Echinoderms There are more than 20 extinct classes In addition, there are five extant classes 1. Asteroidea (sea stars and sea daisies) 2. Crinoidea (sea lilies and feather stars) 3. Echinoidea (sea urchins & sand dollars) 4. Holothuroidea (sea cucumbers) 5. Ophiuroidea (brittle stars)

Classes of Echinoderms

Classes of Echinoderms (Cont.)

Classes of Echinoderms (Cont.)