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Manubrium — The projection of the body of a medusa (jellyfish) 



which bears the mouth. 

 Medusa — Jellyfish. 

 Mesentery — A sheet of leaf -like connective tissue supporting various 



viscera ; in Coelenterates, a partition extending inward 



from the body wall. 

 Notoehord — A cylindrical rod of cells ventral to the spinal cord 



and dorsal to the alimentary tract. Occurs in Chordate 



embryos. 

 Nematocysts — Stinging cells in Coelenterata. 

 Operculum — A plate used for closing the shell of gastropod mol- 



lusks. 

 Orifaee — Opening. 



Oseulum — The excurrent opening in sponges. 

 Para podium — A flat fleshy segmental appendage found in many 



marine annelid worms ; used for locomotion and respira- 

 tion. 

 Pediccllariac — Minute pincer-like organs on the external surface of 



starfish. 

 Pclagie — Pertaining to the open sea— not near shore. 

 Plankton — Animals and plants that drift on the surface of the 



water ; usually without much ability of locomotion. 

 Planula — The free-swimming, usually pear-shaped ciliated body, 



into which the egg of a hydroid develops. 

 Pleistocene — The most recent period of geologic time ; frequently 



spoken of as "The Great Ice Age". 

 Proboscis — The portion of the hydranth body that usually surmounts 



the basal tentacles and which contains the mouth. In 



other animals a tubular extension of any part of the body. 

 Polyp — An individual member of a hydroid colony. 

 Rostrum — A projection of the carapace in crustaceans. 

 Seta — A bristle in worms. 

 Siphon — A tube-like organ through which water enters and leaves 



the body of mollusks and ascidians. 

 Spat — The larval stage of an oyster. 

 Spicule — A minute calcareous or silicious body in sponges or echino- 



derms. 

 Strobila — The attached compound stage in the Scyphozoa. 

 Tentacle — An elongated tactile organ. 

 Thorax — The body division of Arthropods following the head ; 



the neck region. 

 Tube feet — Tubular locomotor organs in echinoderms. 

 Umbrella — Curved or cup-like body of a jellyfish. 

 Umbilicus — The depression in gastropod shells at the base of the 



axis. 

 Velum — The circular muscular membrane of medusae. 

 Zooecium — An individual belonging to a bryozoan colony. 

 Zoo id — A member of a hydroid colony. 



