4d cell—Mesentoblast; a blastomere cell that results from zygotes that have spiral cleavage divisions, and contains an unidentified cytoplasmic factor that causes the cell and its progeny to form mesoderm.

Abdomen—The posterior of the main body divisions.

Abyssal—Of, or relating to, the deepest regions of the ocean.

Acanthor—First larval stage of acanthocephalans.

Aciculum—Small needlelike structure resembling a rod that supports the divisions of the parapodium.

Acoelomate—An organism, particularly an invertebrate, lacking a coelom that is characterized by bilateral symmetry.

Actinotrocha—Tentacle-like ciliated larva of phoronids.

Aestivation—A period of dormancy that is entered into when conditions are not favorable, particularly during very warm or very dry seasons.

Aflagellate—An organism that lacks a flagella.

Agamete—Nucleus within the plasmodium that divides mi-totically and gives rise to a sexual adult.

Ametabolous—Development in which little or no external metamorphic changes are noticeable in the larval to adult transition.

Amphiblastula—Free-swimming larval stage of sponges.

Anal—Relating to or being close to the anus.

Anamorphic—Development in which only part of the adult segments are present in recently hatched young.

Ancestrula—Zooid that develops from an egg.

Antibiosis—A provocative association between organisms that is detrimental, inhibitive, and preventative to one or more of them but produces a metabolic product in another.

Aphotic zone—Region of the ocean where no sun light reaches and exists in complete darkness.

Apical field—An area inside the circumapical band of rotifers that is devoid of cilia.

Arboreal—An organism that lives in, on, or among trees.

Ascidiologists—Scientists who study the Ascidiacea.

Auricularia—Primary larval stage in holothuroid development.

Autapomorphy—A derived trait unique to a taxonomic group.

Benthic—An organism that lives on the bottom of the ocean floor.

Bipinnaria—Free-swimming larval stage of asteroids.

Bivoltine—The production of two broods or generations in a season or year.

Blastomere—Zygote cleavage divisions that result in a cell.

Blastopore—The first opening of the early digestive tract.

Blastula—Sphere of blastomeres.

Brachiolaria—Second stage of asteroid larva.

Brood—When the care of eggs takes place outside or inside of the mother's body for at least the early part of development.

Buccal cavity—A cavity that is present within the mouth.

Bud—The development of new progeny cells or new outgrowth.

Caudal—Referring or pertaining to the posterior end of the body.

Cephalic—Referring or pertaining to the anterior end of the body.

Cephalothorax—The body region that consists of the head and thoracic segments.

Chelicera—Pair of appendages present in the anterior body of arachnids.

Chorion—The shell or covering of an egg.

Cilia—Outgrowth present on the cell surface that is short and produces a lashing movement capable of creating locomotion.

Cleavage—The process of cellular divisions in a fertilized egg that changes it from a single-celled zygote into a multicellular embryo.

Cloaca—Chamber into which the intestinal and urogenital tracts discharge.

Cnidocytes—Prey-capture and defensive cells unique to cnidarians.

Coelom—The epithelium-lined space between the body wall and the digestive tract.

Colony—Body composed of zooids that share resources.

Commensalism—Symbiotic relationship between two or more species in which no group is injured, and at least one group benefits.

Commercial fishery—The industry of catching a certain species for sale.

Communal—Cooperation between females of one species in production and building, but not in caring for the brood.

Conspecific—Belonging to the same species.

Coracidium—Ciliated free-swimming stage of cestode.

Cosmopolitan—Occurring throughout most of the world.

Cuticle—The noncellular outer layers of the body.

Cydippid—Free-swimming ctenophore larva.

Cyphonarutes—Planktonic larva of some nonbrooding gymnolaemate bryozoans.

Definitive host—See Primary host.

Demersal—Aquatic animals that live near, are deposited on, or sink to the bottom of the sea.

Dentate—Having teeth, or structures that function as teeth.

Denticles—Teeth, or structures that function as, or are derived from, teeth.

Deposit feeders—Animals that feed upon matter that has settled on the substrate.

Desmosomes—Structures involved in cellular adhesion.

Detritus—Fragments of plant, animal, or waste remnants.

Deuterostome—Division of the animal kingdom that includes animals that are bilaterally symmetrical, have indeterminate cleavage and a mouth that does not arise from the blastopore.

Diapause—A period of time in which development is suspended or arrested and the body is dormant.

Dioecious—Organisms that have male reproductive organs in one individual and female in another.

Diverticulum—A pouch or sac on a hollow structure or organ.

Doliolaria—Barrel-shaped larval stage.

Ecdysis—Molting or shedding of the exoskeleton.

Ectoparasite—A parasite that lives on the outside of a host.

Endemic—Belonging to or from a particular geographical region.

Endocuticle—The innermost layer of the cuticle.

Endoparasite—A parasite that lives inside the body of its host.

Endosymbiont—Symbiotic relationship in which a sym-biont dwells within the body of its symbiotic partner.

Epicuticle—The surface layers of the cuticle.

Epiphragm—Temporary mucus door over the aperture (opening) that hardens to seal the snail inside.

Epithelium—Membranous tissue that covers the body or lines a body cavity or tube.

Epizoic—An animal or plant that lives on another animal or plant.

Estuary—A semi-enclosed body of water that is diluted by freshwater input and has an open connection to the sea. Typically, there is a mixing of sea and fresh water, and the influx of nutrients from both sources results in high productivity.

Eukaryote—A cell with a nucleus that contains DNA; or an organism made up of such cells.

Eurybathic—An animal that occurs in a wide range of depths.

Euryhaline—An animal that occurs in a wide variety of salinities.

Eurythermic—An animal that occurs in a wide range of temperatures.

Eversible—Capable of being turned inside out.

Exocuticle—Hard and darkened layer of the cuticle lying between the endocuticle and epicuticle.

Exoskeleton—The external plates of the body wall.

Fibrillae—Small filaments, hairs, or fibers.

Fishery—The industry of catching fish, crustaceans, mol-lusks or other aquatic animals for commercial, recreational, subsistence or aesthetic purposes.

Fusiform—Having a shape that tapers toward each end.

Gametogenesis—Production of gametes (sex cells).

Ganglion—A nerve tissue mass containing cell bodies of neurons external to the brain or spinal cord.

Girdle—Outer mantle of the polyplacophoran that is thick and stiff, extending out from the shell plate.

Glycocalyx—Protein and carbohydrate surface coat in cells.

Gonochoric—An animal with separate sexes.

Gonopore—Reproductive aperture or pore present in the genital area.

Gonozooid—A reproductive zooid of a hydroid.

Gynandromorph—An individual that exhibits both male and female characteristics.

Hematophagous—A group that feeds or subsides on blood.

Hemitransparent—Half or partially transparent.

Hermaphrodite—An organism that has both male and female sexual organs.

Heterothermic springs—Springs (of water) that may freeze in the winter.

Heterotroph—An organism that is unable to produce its own food, but must obtain its nutrition by feeding on other organisms.

Higgins larva—Loriciferan larval stage.

Holoplankton—An animal that lives in plankton all of its life.

Homothermic springs—Those with a constant temperature throughout the year.

Host—The organism in or on which a parasite lives.

Hyaline—Transparent, clear, and colorless.

Hydromedusa—Medusa of the hydrozoans.

Hyperparasite—A parasitic organism whose host is another parasite.

Infauna—An animal that lives among sediment.

Inquiline—Animal that lives in the nests or abode of another species.

Integument—A layer of skin, membrane, or cuticle that envelops an organism or one of its parts.

Intermediate host—Host for the larval stage of a parasitic organism.

Intracytoplasmic—Located within or taking place within a cell's cytoplasm.

Kinesis—A movement that lacks directional orientation and depends upon the intensity of stimulation.

Lamina—Thin, parallel plates of soft vascular sensitive tissue.

Larva—An immature development stage.

Larviparous—Eggs brooded within the female that are later released as larvae.

Lecithotrophic—Larvae that do not feed, but rather derive nutrition from yolk.

Lorica—Specialized girdle-like structure made of a set of hardened parts that protect the body, named for the segmented corselet of armor worn by Roman soldiers.

Lumen—Cavity of a tubular organ.

Mandible—The jaw.

Manubria—Tube that bears the mouth and hangs down from the subumbrella or medusae.

Maxilla—One of two components of the mouth immediately behind the mandibles.

Medusae—Well-developed cnidarian that is gelatinous and free-swimming.

Meiosis—Cellular process that results in the number of chromosomes in gamete-producing cells (usually sex cells) being reduced to one half.

Mesoderm —Tissue derived from the three primary embryonic germ layers, and the source of many bodily tissues and structures.

Metachronous—Using coordinated waves, as in bands of cilia beating metachronously.

Metamorphosis—A change in physical form or substance.

Miracidium—Free-swimming first larva of trematodes that is ciliated.

Mitosis—A process that takes place in the nucleus of a dividing cell that results in the formation of two new nuclei having the same number of chromosomes as the parent nucleus.

Moult—The shedding of the exoskeleton.

Mutualism—Symbiotic relationship in which both members of the relationship benefit.

Myoepithelial—Cells of the epithelium.

Nematocyst—Stingers of cnidarians.

Neoblasts—Undifferentiated cells that form the blastema, which precedes regeneration in planarians.

Neritic—An organism that inhabits the region of shallow water adjoining the seacoast.

Nocturnal—An organism that is active mostly at night.

Obligate ectoparasites—External parasites that cannot complete their cycle when removed from their host.

Oocyte—The egg before it has reached maturation.

Ootheca—The cover or case that surrounds a mass of eggs.

Oozoid—The zooid that develops from the fertilized egg of urochordates.

Ophiopleuteus—Planktonic larva of echinoids (urchins).

Oral lamella—Oral membrane or layer.

Oviparous—An organism that lays eggs.

Ovipositor—The apparatus through which the female lays eggs.

Ovoviviparous—An organism that produces young that hatch out of their egg while still within their mother.

Paedomorphosis—Retention of juvenile characteristics by adults.

Paraphyletic—A group that contains some of the descendants of a common ancestor.

Parapodium—Appendage present on annelids that resem- G

bles a paddle. O

Parasite—An organism that lives in or on the body of Y

another living organism, feeding off of its host.

Parenchymula—Larval sponge.

Parthenogenetic—Development of an egg without fertilization.

Pelagic—Organisms that live in the open sea, above the ocean floor.

Pelagosphera—Second planktotrophic larva of sipunculans.

Pentaradial symmetry—Five-part radial symmetry, as seen in echinoderms.

Petancula—Stage of metamorphosis for holothuroids.

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.

Plasmodium—A life cycle stage in which several young organisms join to form a mass of protoplasm.

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.

Polyphyletic—A group that does not contain the most recent ancestor of the organisms.

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 definitive host.

Protandric hermaphrodites—Animals 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.

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

Spicule—A slender, pointed structure.

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.

Stereom—A unique skeletal microstructure (a network of interconnected holes) in echinoderms.

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.

Stomochord—A hollow pouch of the gut found in the proboscis of hemichordates.

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 close 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.

Synapomorphy—A derived trait shared by two or more taxonomic groups.

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.

Totipotency—The ability of a cell to differentiate into any type of body cell.

Triploblastic—Embryos with three germ layers.

Triradial symmetry—Three-part radial symmetry, as seen in the life stages of some echinoderms.

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.

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. I

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

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

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