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Chapter 8Chapter 8““Lower” Invertebrates I: Sponges & RadiataLower” Invertebrates I: Sponges & Radiata

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.

What Are Animals? Animals:

1. multicellular2. eukaryotic cells without cell walls3. cannot produce their own food4. Invertebrates or vertebrates

(most animals are invertebrates)

SpongesPhylum Porifera

•Basic characteristics:– no tissues or organs– asymmetric– sessile

Anon. Wiki Commons

Sponge Structure and Function

Sponge Structure and Function3 basic body forms: leuconoid from most efficient, most common

Sponge Structure and Function• Nutrition and digestion

– suspension/filter feeders– collar cells (choanocytes) filter out tiny food

particles – pinacocytes and archaeocytes (a.k.a.

amoebocytes) ingest larger food particles by phagocytosis

– Most food digested and distributed to other cells by archaeocytes

Sponge Structure and Function• Reproduction in sponges

– asexual reproduction• budding• fragmentation

– sexual reproduction• most hermaphrodites• eggs from archaeocytes and sperm from modified collar cells

Figure 8-4 p193

Fertilization

Sperm cell engulfed by a choanocyte

Egg cell Sperm cell (modified choanocyte)

Embryo

Sexual reproduction

Planktonic amphiblastula larva

Asexual reproduction

New sponge

New spongeLarva settles and attaches to bottom or other surface

Bud

Ecological Roles of Sponges• Competition

– corals and bryozoans

• Predator-prey relationships– few species eat sponges

• spicules• chemical deterrents

Ecological Roles of Sponges

• Symbiotic relationships– mutualistic or commensalistic hosts – organisms live within the canals

Ecological Roles of Sponges

• Sponges and nutrient cycling– boring sponges

Cnidarians: Animals with Stinging Cells

• Include jellyfish, hydroids, corals and sea anemones

• cnidocytes

ErgoSum88

Organization of the Cnidarian Body

Stinging Cells

• Cnida– nematocysts

Stinging Cells

• Dangerous species– Portuguese man-of-war– box jellyfish

Types of Cnidarians• Hydrozoans or Hydroids

– mostly colonial– colonial forms contain

2 types of polyp:• Feeding polyp• Reproductive polyp

– hydrocorals secrete a calcareous skeleton

– some produce floating colonies (e.g. P. man-o-war)

Types of Cnidarians

• Jellyfish– scyphozoans—true jellyfish (class Scyphozoa)

• plankton• medusa is predominant• photoreceptors

Types of Cnidarians

• Box jellyfish– box jellyfish (class

Cubozoa)• box-shaped bells• relatively strong swimmers• tropical• complex eyes (image-

forming?)• voracious predators,

primarily of fish

Types of Cnidarians

• Anthozoans (class Anthozoa)– include sea anemones,

corals and gorgonians – sea anemones

• benthic• gastrovascular cavity

divided• though sessile, many can

change locations

Types of Cnidarians

• Anthozoans (class Anthozoa)– coral animals

• polyps secrete a calcium carbonate skeleton

• stony corals form reefs

Nick Hobgood

Types of Cnidarians

• Anthozoans (class Anthozoa)– soft corals

• polyps that form plant-like colonies

Nutrition and Digestion• Gastrovascular cavity

– digestion and transport– 1 opening: mouth/anus

• Many suspension feeders• Jellyfish and box jellyfish are carnivorous• Sea anemones generally feed on invertebrates,

some large species feed on fish, shallow water species have symbiotic algae

Reproduction

• asexual polyp stage – fission, budding common in corals– strobilation common in hydroids and jellyfish

• sexual medusa stage

Reproduction

• Anthozoans– asexual reproduction IS COMMON

• pedal laceration• fission• budding

– sexual reproduction• male and female forms, gametes are released• planula larva

Ecological Relationships of Cnidarians

• Predator-prey relationships– cnidarians are predators– stinging cells discourage

predation– sea turtles, some fish

and molluscs prey on hydrozoans and jellyfish

Ecological Relationships of Cnidarians

• Habitat formation– coral polyps form

complex 3-dimensional structures inhabited by thousands of other organisms

– coral reefs provide a solid surface for attachment, places for pelagic animals to rest and hide and buffer waves and storms

Terry Hughes

Ecological Relationships of Cnidarians

• Symbiotic relationships– Portuguese man-of-war and man-of-war fish– reef-forming corals and zooxanthellae– sea anemones:

• clownfish• hermit crab

Ctenophores

• Planktonic, nearly transparent

• Ctenophore structure– 8 rows of comb plates– radial symmetry– lack stinging cells– bioluminescent

Ctenophores• Digestion and nutrition

– Gastro-vascular cavity– feeds on plankton, larval fish and fish eggs– branched tentacles, adhesive cells, jellyfish

stingers to capture prey