PHYLUM ARTHROPODA 



221 



CLASSIFICATION OF 

 THE CRUSTACEA 



{For reference purposes only) 



Class Crustacea are arthropods, most of 

 which hve in water and breathe by means of 

 gills. Symmetry is bilateral; they are triploblas- 

 tic, and the body consists of a longitudinal 

 series of segments. The body is divided into 

 head, thorax, and abdomen, or the head and 

 thorax may be fused, forming a cephalothorax. 

 The head consists of different numbers of 

 fused segments in different groups; it bears 

 two pairs of antennae (feelers), one pair of 

 mandibles (jaws), and two pairs of maxillae. 

 The appendages are jointed. Only five sub- 

 classes and one order are listed here. 



Subclass 1. Branchiopoda. This is the most 

 primitive group of crustaceans. 

 Free-swimming; thoracic ap- 

 pendages leaflike and respira- 

 tory; usually a carapace. Ex. 

 Eubranchipus vernalis (Fig. 

 110). 



Subclass 2. Ostracoda. Free-swimming, cara- 

 pace bivalved; appendages not 

 leaflike. Ex. Eucypris virens 

 (Fig. 110). 



Subclass 3. Copepoda. Free-swimming, par- 

 asitic, or commensal; no com- 

 pound eyes; typically with 6 

 pairs of thoracic legs. Ex. 

 Cyclops (Fig. 110). 



Subclass 4. Cirripedia. Barnacles. Adults 

 sessile and attached, or para- 

 sitic; no compound eyes in 

 adults; carapace enclosing body, 

 usually with limb plates; mostly 

 hermaphroditic. Ex. Lepas 

 (Fig. 110). 



Subclass 5, Malacostraca (Fig. 121). Mostly 

 large, but some small, such as 



the sow bugs. Fig. 110; usually 4 

 segments in head, 8 in thorax, 

 and 6 in abdomen; gastric mill 

 in stomach. Only one order 

 listed here. 



Order Decapoda. Lobsters, crayfish, shrimps, 

 crabs, etc. Carapace large, covering thorax; 

 eyes on stalks; 5 pairs of walking legs. Ex. 

 Orconectes, crayfish (Fig. Ill); Hoynarus, 

 lobster. 



Class Trilobita. The trilobites (Fig. 122) 

 were marine animals, probably allied to the 

 crustaceans; they are all extinct. The best- 

 known species, Triarthrus becki, occurs in the 

 Utica shale (Lower Silurian) of New York 

 State. 



SELECTED COLLATERAL 

 READINGS 



Borradaile, L.A., and Yapp, W.B. Manual of 

 Elementary Zoology. Oxford Univ. Press, 

 New York, 1958. 



Huxley, T.H. The Crayfish, an Introduction 

 to the Study of Zoology. Kegan, Paul, 

 Trench, Trubner, London, 1880. 



Pennak, R.W. Freshwater Invertebrates of the 

 United States. Ronald Press, New York, 

 1953. 



Pratt, H.S. A Manual of Common Inverte- 

 brate Animals. Blakiston, Philadelphia, 1935. 



Snodgrass, R.E. "Evolution of the Annelida, 

 Onychophora, and Arthropoda." Smith- 

 sonian Misc. Collections, 97:1-159, 1938. 



Snodgrass, R.E. A Textbook of Arthropod 

 Anatomy. Comstock Publishing Associates, 

 Ithaca, N.Y., 1952. 



Ward, H.B., and Whipple, G.C. Fresh-water 

 Biology. Wiley, New York, 1918. 



Wilson, R.C. "A Review of the Southern Cali- 

 fornia Spring Lobster Fishery." California 

 Fish and Game, 34:71-80, 1948. 



