1. Sponges, Cnidarians, Comb Jellies, and Marine Worms
Chapter 8
Sponges, Cnidarians, Comb Jellies, and Marine Worms

2. Key Concepts
Sponges are asymmetric, sessile animals that filter food from the water circulating through their bodies.
Sponges provide habitats for other animals.
Cnidarians and ctenophores exhibit radial symmetry.
Cnidarians possess a highly specialized stinging cell used to capture prey and for protection.

3. Key Concepts Marine worms exhibit bilateral symmetry.
Turbellarians are free-living flatworms; flukes and tapeworms are parasitic flatworms.
Nematodes are abundant and important members of the meiofauna.
Polychaete diversity stems from the evolution of a segmented body that allows increased motility.

4. Key Concepts
In addition to being important consumer organisms, polychaetes are the primary prey of many marine animals and play an important role in recycling nutrients.
Several other groups of wormlike animals, including ribbon worms, spiny-headed worms, peanut worms, acorn worms, and beardworms, play important ecological roles in the marine environment.

5. What Are Animals? Animals: are multicellular
distinguishes them from bacteria and most protists
have eukaryotic cells without cell walls
distinguishes them from bacteria, fungi, algae and plants
cannot produce their own food, so they depend on other organisms for nutrients
can actively move (with the exception of adult sponges)

6. Sponges Phylum Porifera Basic characteristics: simple asymmetric
sessile—permanently attached to a solid surface
have many shapes, sizes and colors

7. Sponge Structure and Function
Body is built around a system of water canals
ostia—tiny holes or pores through which water enters the sponge’s body
spongocoel—spacious cavity in the sponge
osculum—large opening through which water exits from the spongocoel

9. Sponge Structure and Function
Lacking tissues, sponges have specialized cells
collar cells (choanocytes) use their flagella to provide force for moving water through the sponge’s body
pinacocytes in a layer provide an outer covering for the sponge
archaeocytes—cells that resemble amoebas, and can move through the body
can assume any of the other cell forms, or transport materials

10. Sponge Structure and Function
Structural materials
spicules—skeletal elements that give support to a sponge’s body, which are produced by specialized cells and composed of calcium carbonate, silica or spongin
spongin—a protein that forms flexible fibers

11. Sponge Structure and Function
Sponge size and body form
size is limited by water circulation
asconoid—simplest form; tubular and always small
syconoid—sponges that exhibit the first stages of body-wall folding
leuconoid—sponges with the highest degree of folding, which have many chambers lined with collar cells

13. Sponge Structure and Function
Nutrition and digestion
sponges are suspension feeders – they feed on material that is suspended in seawater
sponges are filter feeders – they filter their food from the water
sponges are one of the few animals that can capture particles 0.1 to 1.0 micrometers in size

14. Sponge Structure and Function
Reproduction in sponges
asexual reproduction
budding—a group of cells on the outer surface of the sponge develops and grows into a tiny new sponge, which drops off
fragmentation—production of a new sponge from pieces that are broken off
sexual reproduction
eggs usually develop from archaeocytes and sperm from modified collar cells
larval stage is a planktonic amphiblastula

16. Ecological Roles of Sponges
Competition
compete for space to attach with corals and bryozoans
Predator-prey relationships
few species eat sponges
spicules are like needles
some produce chemical deterrents
major food source for hawksbill sea turtle

18. Ecological Roles of Sponges
Symbiotic relationships
sponges are mutualistic or commensalistic hosts to many organisms
e.g. mutualistic bacteria
many organisms live within the canals or spongocoel, for protection, water flow

20. Ecological Roles of Sponges
Sponges and nutrient cycling
boring sponges recycle calcium as they burrow into coral and mollusc shells

23. Cnidarians: Animals with Stinging Cells
Phylum Cnidaria
Named for their cnidocytes—stinging cells
Cnidocytes are used to capture prey and protect the animal

24. Organization of the Cnidarian Body
Radial symmetry—many planes can be drawn through the central axis that will divide the animal into equivalent halves
Often exhibit 2 body plans within their life cycles:
polyp—a benthic form characterized by a cylindrical body with an opening at 1 end
medusa—a free-floating stage (jellyfish)

27. Stinging Cells
Cnida—stinging organelle within a cnidocyte, which may function in locomotion, prey capture, or defense
nematocysts—spearing type, which are discharged when the cnidocill—a bristle- like trigger—contacts another object

29. Stinging Cells Dangerous species
Portuguese man-of-war (painful stings)
box jellyfish (can kill within 3-20 minutes)

32. Types of Cnidarians Hydrozoans (class Hydrozoa) mostly colonial
colonial forms contain 2 types of polyp:
feeding polyp—functions in food capture
reproductive polyp—specialized for reproduction
hydrocorals secrete a calcareous skeleton
some produce floating colonies
e.g. Portuguese man-of-war

37. Types of Cnidarians Jellyfish and box jellyfish
scyphozoans—true jellyfish (class Scyphozoa)
medusa is predominant life stage
photoreceptors—sense organs that can determine whether it is dark or light
box jellyfish (class Cubozoa)
tropical
voracious predators, primarily of fish

40. Types of Cnidarians Anthozoans (class Anthozoa) sea anemones
polyps with a vascular cavity divided into compartments radiating from the central one
though sessile, many can change locations

42. Types of Cnidarians Anthozoans (class Anthozoa) coral animals
polyps that secrete a hard or soft skeleton
form reefs along with types of algae

45. Types of Cnidarians Anthozoans (class Anthozoa) soft corals
polyps that form plant-like colonies

48. Nutrition and Digestion
Gastrovascular cavity—central cavity where cnidarians digest their prey
functions in digestion and transport
Many hydrozoans and anthozoans are suspension feeders
Jellyfish and box jellyfish eat fish and larger invertebrates
Sea anemones generally feed on invertebrates

50. Reproduction Hydrozoans
generally exhibit asexual polyp stage and sexual medusa stage in the life cycle
reproductive polyps form medusa-like buds which grow into adults after release
adults release gametes into the water, where they are fertilized and form larvae
planula larva—planktonic larva that grows in the water column, then settles

52. Reproduction Scyphozoans
medusae (sexual stage) release gametes into the water for fertilization
planula larvae settle, grow into polyps, and reproduce medusa-like buds asexually

54. Reproduction Anthozoans asexual reproduction sexual reproduction
pedal laceration—leaving parts of the pedal disk (base) behind to grow into new animals
fission—the anemone splits in two and each half grows into a new individual
budding produces large colonies of identical hard corals
sexual reproduction
larval stage is a planula larva

55. Ecological Relationships of Cnidarians
Predator-prey relationships
cnidarians are predators
stinging cells discourage predation
Habitat formation
coral polyps form complex 3-dimensional structures inhabited by thousands of other organisms
coral reefs provide a solid surface for attachment, and buffer waves and storms

56. Ecological Relationships of Cnidarians
Symbiotic relationships
Portuguese man-of-war and man-of-war fish
reef-forming corals and zooxanthellae
sea anemones...
and clownfish
and the hermit crab

59. Ctenophores Phylum Ctenophora Planktonic, nearly transparent
Ctenophore structure
named for 8 rows of comb plates (ctenes) which the animal uses for locomotion
ctenes are composed of large cilia
exhibit radial symmetry
bioluminescent

61. Ctenophores Digestion and nutrition
carnivorous, feeding on other planktonic animals
may used branched tentacles in a net pattern, adhesive cells, jellyfish stingers

63. Ctenophores Reproduction almost all are hermaphroditic
fertilization may be in the water column, or eggs may be brooded in the body
cydippid larva—free-swimming larva resembling the adult ctenophore

64. Marine Worms
Have elongated bodies, most lacking any kind of external hard covering
Most exhibit a hydrostatic skeleton— support is provided by body fluid
Types of marine worms include:
flatworms
nematodes
annelid worms
others

65. Flatworms Have flattened bodies with a definite head and posterior end
Trubellarian flatworms (class Turbellaria) are free-living
Flukes (class Trematoda) and tapeworms (class Cestoda) are parasitic
Bilateral symmetry—body parts are arranged in such a way that only one plane through the midline of the central axis will divide the animal into similar right and left halves

69. Flatworms
Bilateral symmetry favors cephalization—the concentration of sense organs in the head region
Types of flatworm
turbellarians are mostly pelagic, and are common members of meiofauna (invertebrates living between sediment particles)
flukes usually have complex life cycles
tapeworms live in the host’s digestive tract

70. Flatworms Reproduction
can reproduce asexually and regenerate missing body parts
sexual reproduction
reciprocal copulation—when hermaphrodites fertilize each other
some have no larval stage; others have free- swimming planktonic larva

71. Nematodes Phylum Nematoda
Roundworms – the most numerous animals on earth
Important as scavengers or parasites
Many free-living nematodes are carnivorous
Most are hermaphroditic, but some have separate sexes

73. Annelids: The Segmented Worms
Annelids—worms whose bodies are divided internally and externally into segments
segments increase mobility by enhancing leverage
setae—small bristles used for locomotion, digging, anchorage and protection
Types of marine annelids
polychaetes
echiurans
pogonophorans

75. Polychaetes
Polychaetes (class Polychaeta) are the most common marine annelids
Traditionally divided into 2 groups:
errant polychaetes (move actively)
may be strictly pelagic, crawl beneath rocks and shells, be active burrowers in sand or mud, or live in tubes
sedentary polychaetes (sessile)
e.g. tube worms
create tubes from a variety of materials

78. Polychaetes Feeding and digestion
some errant species are active predators; tube dwellers may partially or completely leave the tube to feed
many sedentary species are filter or suspension feeders
digestive tract is usually a straight tube from the mouth to the posterior anus
food enters the mouth, nutrients are absorbed in the intestine, and wastes are excreted through the anus

81. Polychaetes
deposit feeders—animals that feed on organic material mixed with mineral deposits which settle on the sea bottom
nonselective deposit feeders ingest both organic and mineral particles, digest the organic particles, and excrete the minerals
fecal casts—piles of defecated undigested materials
selective deposit feeders separate organic materials from minerals and ingest the former

84. Polychaetes Reproduction in polychaetes
asexual reproduction via budding or fragmentation occurs in some polychaetes
most reproduce only sexually, with the majority having separate sexes
gametes are released into the water
epitoky—the formation of a pelagic reproductive individual (epitoke) that is different from the non-reproductive form

87. Polychaetes epitoky in polychaetes
swarming—males and females come to the surface in large numbers at night to shed sperm and eggs
swarming of epitokes occurs only at specific times of year, and seems related to lunar cycles and tides

88. Echiurans Spoonworms (class Echiura)
Sausage-shaped annelids resembling sipunculid worms
Mostly deposit feeders; at least 1 is a filter feeder
deposit feeders typically have a flat, ribbon-like proboscis (tube extending from the mouth) to collect particles
Have separate sexes, shed gametes into the water, and have a planktonic larval stage

90. Pogonophorans Beardworms (class Pogonophora)
Live in buried tubes and have a cylindrical body with a ring of tentacles around the anterior end
Lack mouth or digestive tract
May absorb nutrients dissolved in the water or obtain nourishment from chemosynthetic bacteria (those living in vent communities)

91. Other Marine Worms Other worm-like animals live in the sea
Anatomically and developmentally different
Types include:
ribbon worms
sipunculids
priapulids
hemichordates
gastrotrichs, nematomorphs, acanthocephalans

92. Ribbon Worms Phylum Nemertea
Have ribbon-like bodies; similar to flatworms, but longer and thicker
Mostly benthic (some deepwater species are pelagic)
Some reproduce asexually by fragmentation; most have separate sexes and external fertilization
Carnivorous, catching prey (annelids, crustaceans) with a proboscis

94. Sipunculids Phylum Sipuncula
Solitary benthic worms that live in burrows in mud or sand, empty mollusc shells, or coral crevices
Some known as peanut worms – they contract into a peanut shape when disturbed
Either suspension or deposit feeders; have a proboscis and ring of tentacles
Separate sexes, external fertilization; may either develop directly into worms or have a larval stage

96. Priapulids
Benthic worms that bury themselves in sand and mud in shallow or deep water
Small species belong to meiofauna; may be deposit or suspension feeders
Larger species are thought to be carnivorous
Have separate sexes; fertilization is external in large species but probably internal in smaller ones; larvae inhabit benthic mud

98. Hemichordates Acorn worms (phylum Hemichordata)
Sessile bottom dwellers that burrow in sediments of intertidal mud or sand flats or under stones
Collects food with a large proboscis
Some species use their proboscis to dig burrows; the head protrudes from one end of the burrow, while the anus deposits fecal material near the other

100. Gastrotrichs, Nematomorphs, and Acanthocephalans
Gastrotrics (phylum Gastrotricha)
small worms inhabiting spaces between sediment particles, surface of detritus, and surfaces of submerged plants/animals
Neatomorphs, or horsehair worms (phylum Nematomorpha)
name derived from resemblance to the hairs of a horse’s tail
free-living as adults
parasites of arthropods as juveniles

101. Gastrotrichs, Nematomorphs, and Acanthocephalans
Acanthocephalans, or spiny-headed worms (phylum Acanthocephala)
parasites, mostly of fish, birds and mammals
name is derived from cylindrical proboscis with several rows of spines, which is used to penetrate the intestine of the host

102. Ecological Roles of Marine Worms
Nutrient cycling
as burrowing organisms, they release nutrient buried in the ocean bottom back to the surface for use by producers
Predator-prey relationships
important links in food chains – consume organic matter unavailable to larger consumers, and then become food for larger consumers themselves

103. Ecological Roles of Marine Worms
nematodes are the most abundant members of meiofauna
echiurans may be significant in the diet of some fishes
polychaetes are a major food source for invertebrates and vertebrates
Symbiotic relationships
non-carnivorous tube-dwelling and burrowing polychaetes provide a retreat for commensal organisms

104. Ecological Roles of Marine Worms
Population dynamics
populations may be limited by physical or biological factors
infaunal polychaetes do not appear to be limited by resources, but by predation
size of the polychaete population increased 2 or 3 times when areas in the York River estuary of the Chesapeake Bay were protected form predatory fish and crabs by wire cages