ch 34: invertebrates

what is an invertebrate?

an animal without a backbone

what percent of animal species are invertebrates?

95%

what is a ctenophore, aka comb jellies?

one of the earliest animals, less than 100 species. all marine and look similar to jellyfish

what is significant about ctenophores (comb jellies)

first complete gut: mouth, gastrovascular cavity and two anal pores. this allows digestion of bigger prey pieces.

what are porifera?

the sponges. it is one phylum, with over 8,000 mostly marine species.

what are some characteristics of porifera?

loosely organized, lacking true tissues, multicellular, no apparent symmetry, range from a few mm to over 2 m in diameter. adults are sessile, while larvae are free-swimming

what is the spongocoel?

central cavity in the sponge

sponge structure

water drawn through pores into spongocoel and flows out through osculum at top. spicules (skeletal fibers) or spongin for support. some species produce defensive chemicals

what lines the spongocoel?

choanocytes. they trap and eat small particles and plankton, similar to cells of protist choanoflagellates.

what is between choanocytes and epithelial cells?

mesohyl. it contains amoebocytes which absorbs food from choanocytes, digest it, and carry nutrients to other cells

sponge sexual reproduction

most are hermaphrodites. sperm is released in water to fertilize eggs in mesohyl of nearby sponges, then zygotes develop into swimming larvae

sponge asexual reproduction

small fragment or bud may detach and form a new sponge

Cnidaria phylum

contains jellyfish and other radially symmetric animals. some examples are jellyfish, box jellies, hydra, sea anemonies, and corals.

what are the two body forms of cnidaria?

sessile polyp and motile medusa

sessile polyp

tubular body with tentacles surrounding opening (serves as mouth and anus). one end is attached to substrate. could be single (ex. sea anemones) or colonial (corals)

motile medusa

umbrella shaped body with a mouth on the underside surrounded by tentacles. may have simple sensory organs near bell margin. statocysts for equilibrium, ocelli are light sensitive. (ex jellyfish)