Summarizing Phylum Cnidaria

Summary

Cnidarians represent a more complex level of organization than Porifera. They possess outer and inner tissue layers that sandwich a noncellular mesoglea. Cnidarians possess a well-formed digestive system and carry out extracellular digestion. The cnidocyte is a specialized cell for delivering toxins to prey as well as warning off predators. Cnidarians have separate sexes and have a lifecycle that involves morphologically distinct forms. These animals also show two distinct morphological forms—medusoid and polypoid—at various stages in their lifecycle.

Glossary

Cnidaria

phylum of animals that are diploblastic and have radial symmetry

cnidocyte

specialized stinging cell found in Cnidaria

epidermis

outer layer (from ectoderm) that lines the outside of the animal

extracellular digestion

food is taken into the gastrovascular cavity, enzymes are secreted into the cavity, and the cells lining the cavity absorb nutrients

gastrodermis

inner layer (from endoderm) that lines the digestive cavity

gastrovascular cavity

opening that serves as both a mouth and an anus, which is termed an incomplete digestive system

medusa

free-floating cnidarian body plan with mouth on underside and tentacles hanging down from a bell

mesoglea

non-living, gel-like matrix present between ectoderm and endoderm in cnidarians

nematocyst

harpoon-like organelle within cnidocyte with pointed projectile and poison to stun and entangle prey

polyp

stalk-like sessile life form of a cnidarians with mouth and tentacles facing upward, usually sessile but may be able to glide along surface

polymorphic

possessing multiple body plans within the lifecycle of a group of organisms

siphonophore

tubular structure that serves as an inlet for water into the mantle cavity