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a blind, saclike cavity lined by gastrodermis and opening to the exterior via the mouth which functions in extracellular digestion, circulation, excretion, reproduction, and hydrostatic skeletal support

gastrovascular cavity

another name for a coelenteron


arranged in one or more whorls that surround the mouth of a cnidarian

radial symmetry

a body plan where a vertical section along an axis or through any radius produces mirror-image halves

oral aboral axis

a body arrangement that extends from the mouth to the base


a body form of a cnidarian that resembles a flower and its stalk

pedal disc

a structure at the aboral end of a polyp used for attachment


an elevated region, with the mouth at its summit, situated in the center of a cnidarian's oral disc

oral disc

the region of a cnidarian's body with the mouth and manubrium at its center, and a whorl of tentacles at its margin


a chitinous exoskeleton secreted by the pedal disc and column of a polyp that provides protection and attachment to the substratum


a body form of a cnidarian shaped like an umbrella or bell


the oral surface (disc) of a medusa's body


the aboral side of a medusa's body


the outer epithelium of a cnidarian's body


the inner epithelium of a cnidarian's body that lines the coelenteron


a gelatinous extracellular matrix between the epidermis and gastrodermis


a tubular body wall outgrowth that includes the coelenteron, from which zooids bud at intervals along its length

stolonate colony

a cnidarian growth form that consists of a single or branched tubular body wall outgrowth attached to the surface of the substratum, that grows in a two-dimensional network and bears upright, unbranched zooids


a continuous mat-like sheet of stolonate tissue that unites the zooids and attaches the colony to the substratum


a network of hollow gastrodermal tubes, located between the upper and lower epidermal surfaces of the coenosarc, that course through the mesoglea and interconnect the zooidal coelenterons

fruticose colony

an upright, plantlike cnidarian growth form that may be grassy, bushy, shrubby, or feathery in appearance

coronal muscle

the principal halo-shaped, circular muscle of medusae located on the subumbrellar surface

nerve net

a complex two-dimensional system of interconnected neurons located in the epidermis and gastrodermis, joined together by neurons in the mesoglea

diffuse conduction

the radiation of nerve impulses through a nerve net like ripples from a pebble tossed in a pond


a brainlike concentration of neurons that receives sensory input, integrates the information with other inputs, and generates motor output


a combined sensory-effector cell that plays a central role in prey capture and defense; a unique and defining feature of cnidarians


a fluid-filled membranous capsule containing a long tubular invagination of the capsule wall that, upon stimulation, everts explosively to the exterior to sting prey or to adhere to the surface of an animal or substrate


a type of cnida found in all cnidarians that has spines or barbs on the surface of the discharged tubule


a thin-walled cnida occurring only in anthozoans that contains a coiled, spring-like tubule that, when discharged, releases tiny, sticky threads


the central compartment in the cnidarian coelenteron

radial canals

the branches of the cnidarian coelenteron connecting the stomach to the ring canal

ring canal

the branch of the cnidarian coelenteron located around the margin of the body

enzymatic gland cells

the secretory cells lining the gastrodermis which release proteases that digest prey extracellularly


the ciliated, free-swimming planktonic larva of cnidarians that settles to the bottom and metamorphoses into a juvenile


the vertical partitions of gastrodermis and mesoglea that divide the anthozoan coelenteron into radial compartments


the long, threadlike, cnidae-bearing extensions of the septa which spew from the mouth and tentacle tips when the body suddenly deflates; used for defense, prey capture, and extracorporeal digestion of prey


the strongly-developed and conspicuous longitudinal septal muscles of anemones which, upon contraction, invaginate the oral disc and tentacles and shorten the body column

pedal laceration

a specialized form of fragmentation in anemones where small pieces of the pedal disc detach and develop into small anemones


the skeletal cup around the polyp of a stony coral, which the polyp can retract into for protection


the process where zooxanthellae corals expel some or all of their algae due to adverse conditions such as under- or overillumination, excess UV exposure, salinity fluctuation, and low or high temperatures


the taxon that includes cnidarians with a medusa stage in their life cycle, such as Scyphozoa and Hydrozoa


the small, funnel-shaped polyp found in large jellies

septal funnel

a hollow invagination of the oral disc extending deeply into the septa of large jellies

oral arms

four divisions of the manubrium of large jellies that extend below the bell

gastric filaments

the slender, threadlike clusters found at the septal margins of large jellies that bear nematocytes and enzymatic gland cells used in subduing prey and digestion


the rounded, scalloped lobes on the umbrellar margin of large jellies which provide flexion points during bell contraction


the knoblike sensory organs of large jellies consisting of a statocyst, a mechanoreceptor, and a chemoreceptor (and sometimes a photoreceptor); provide information related to gravity-equilibrium, waterborne vibrations (hearing), as well as odor and light detection


the process where scyphistomae asexually reproduce young medusae


a scyphistoma that is asexually-producing disclike medusa from its oral end


in scyphozoans, the newly released, free-swimming, juvenile medusa


a polyp of colonial hydrozoans, each containing a mouth, manubrium, tentacles, and stomach


an iris diaphragm located below the bell of a hydrozoan medusa that creates a powerful water jet as the jelly swims


the sessile, benthic colonies of hydrozoans


the typical feeding hydranths of colonial hydrozoans


the incompletely differentiated medusae of colonial hydrozoans that produce gonads, but lack some or most other medusan traits

medusa buds

produce free-swimming medusae in colonial hydrozoans


the protective or food-catching polyps of colonial hydrozoans that contain batteries of nematocytes


a gas-filled float in siphonophores that provides buoyancy


a class of cnidarians including the sea anemones, corals, sea fans, sea pens, and sea pansies


a class of cnidarians including the large jellyfish, as well as box jellies, stalked jellies, flag-mouth jellies, and root-mouth jellies


a class of cnidarians including the colonial hydroids, Portuguese man-of-war, fire corals, and rose corals, as well as the solitary Hydra

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