Phoresy—Nonparasitic relationship between two organisms in which one uses the other as a means of transportation.

Photokinesis—Activity induced by the presence of light.

Photophore—Cell or group of cells that produce light.

Phytophagous—An organism that solely feeds upon plants.

Pilidium—Free-swimming, planktotrophic larva of het-eronemerteans.

Pinnules—Small branches.

Planktotrophic larvae—Larvae that feed during their planktonic phase.

Planulae—Larval cnidarians.

Pleonite—Also known as abdominal somite. The single division of a body after the thorax.

Pleopod—An appendage originating from the abdomen.

Plerocercoid—Last larval lifestage of tapeworms.

Polyembryony—The production of several embryos from a single egg.

Polyp—Cnidarian form that is sessile.

Polyphagous—An organism that consumes a variety of foods.

Positively phototactic—Movement toward light.

Predaceous—An organism that preys on other organisms.

Predator—An animal that attacks and feeds on other animals.

Primary host—An organism that acts as the host for an adult stage of a parasite. Also called a definitive host.

Protandric hermaphrodites—Animals that hatch as males and later develop into females.

Protonephridia—Ciliated excretory tube that is specialized for filtration.

Protonymph—The second instar of a mite.

Protostome—Bilateral metazoans characterized by determinate and spiral cleavage, the formation of a mouth and anus directly from the blastopore, and the formation of the coelom by the embryonic mesoderm having split.

Pseudovipositor—Terminal abdominal segment of females from which eggs are layed.

Radial symmetry—The exact arrangement of parts or organs around a central axis.

Ramate—An animal or organism with branches.

Raptorial—An organism that has specially adapted the ability to seize and grasp prey.

Rhagon—Stage of development in demosponge larva.

Rostrum— The beak, snout, spine, proboscis, or anterior median prolongation of the carapace or head of an organism.

Saprophytic—An organism that lives on dead or decaying organic matter.

Scalids—Sets of complex spines that allow the organism to move, capture food, or sense changes in its environment.

Scyphistoma—Scyphozoan polyp.

Sclerites—Thick layer of the exoskeleton.

Segment—A rings or subdivisions of the body.

Sensu stricto—In the "strict sense."

Seta—A bristle.

Somites—The similar or identical segments that divide an animal (especially invertebrates) longitudinally.

Spermatophore—Packet of sperm that is usually transferred from one individual to another during mating.

Spiral cleavage—Cleavage pattern in which spindles or places are oblique to the axis of the egg.

Spiralians—Animal groups that show spiral cleavage patterns.

Spirocyst—Adhesive threads present on Cnidarians that capture prey and attach to immobile objects.

Stock—A biologically distinct and interbreeding population within a species of aquatic animals.

Stoloniferous—An organism that bears or develops a branch from its base to produce new plants from buds, or an extension of the body wall that develops buds giving rise to new zooids.

Strobilation—Asexual reproduction by division into body segments.

Subsistence fishery—A fishery in which the harvested resource is used directly by the fisher.

Symbiont—An organism living in a symbiotic relationship with another organism.

Symbiosis—An intimate association, union, or living ar-ragement between two dissimilar organisms in which at least one of the organisms is dependent upon the other.

Synanthropic—Associated with human habitation.

Syncytial—Multinucleate mass of cytoplasm resulting from the fusion of cells.

Taxis—Reflex movement by an organism in relation to a source of stimulation.

Tegument—Outer, nonciliated layer of the body wall of platyhelminth parasites.

Test—Shell-like encasement or skeleton.

Triploblastic—Embryos with three germ layers.

Trochophore—Larva that has a girdle ring of cilia.

Troglophilous—An organism that lives in caves.

Unci—Hooked anatomical structure.

Uncinus—Miniature hooked anatomical structure.

Uniramous—Having one branch, such as only one appendage in crustaceans. Typically results from loss of the appendage.

Univoltine—A group that produces only one generation per year.

Velum—Shelf present under the umbrella of most hydrom-edusae, or a ciliated growth with which larva swim.

Vermiform larva—A legless, worm-like larva without a well-developed head.

Vibrissae—A pair of large bristles that is present just above the mouth in some organisms.

Vitellarium—Part of the ovary that produces yolk-filled nurse cells.

Viviparous—An organism that produces live young.

Zoea—Second to last larval stage of many crustaceans.

Zooid—Individual invertebrate that reproduces nonsexually by budding or splitting, especially one that lives in a colony in which each member is joined to others by living material, for example, a coral.

Zooplankton—Free-swimming, microscopic planktonic animals present in lakes and oceans.

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