GLOSSARY OF TECHNICAL TERMS MOST 

 FREQUENTLY USED. 



Acontia — Long slender threads equipped with nematocysts or sting- 

 ing cells, in sea anemones. 

 Adductor muscle — The muscle used in opening and closing shells 



of bivalve mollusks. 

 Algae — Unicellular plants; sea weeds. 

 Ambulacral groove — The elongate groove on the lower surface 



of the arms of starfish. 

 Antennae — Slender hair-like appendages located on the head of 



various animals ; "feelers." 

 Bivalve — A mollusk composed of two individual valves or shells. 

 Bronchia— A gill. 

 Byssus — A group of threads secreted by the foot of certain 



bivalve mollusks for the purpose of attachment. 

 Carapace — The shell covering the cephalo-thoracic region of crabs 



and other crustaceans. 

 Cephalo thorax — The body-division of crustaceans formed by the 



fusion of the head and neck regions. 

 Cheliped — The pincer or large grasping claw of crabs, lobsters 



and other crustaceans. 

 Chetae — Same as setae 

 Cilia — Small hair-like projections on the outer surface of certain 



animals ; used for locomotion in certain lower forms. 

 Columella — The axis of a spiral gastropod shell. 

 Epidermis — The outer layer or skin. 

 Fascicled — Compound or in bundles. 

 Gonosome — An individual of a hydroid colony which bears the 



reproductive organs. 

 Hydra nth — An individual of a hydroid colony which performs the 



nutritive or digestive functions. 

 Hydrorhiza — The root-like structure by which the hydroid is at- 

 tached to stones, shells or other substrata. 

 Hydrotheca — The chitinous recepticle into which the hydranths 



of many hydroids may retract. 

 Hydroid — The sessile, asexual generation of the Hydrozoa. 

 Lithocyst — A marginal sense organ in certain medusae. 

 Littoral — Pertaining to the seashore, particularly the intertidal 



zone. 

 Madreporic plate — A porous plate on the upper surface of echino- 



derms through which fluids may enter the system. 



257 



