CLA8SIF10ATI0N OF CRU8TA0EA. 305 



Class. I. CEUSTACEA. 



Arthropoda breathmg by gills nituated on the legs, or respiring through 

 the body-walls. Body in, the higher forms dimded into tioo regions, a 

 cephalo-thorax and abdomen. Two pairs of antennm ; mandibles usu- 

 ally with a palpus. Heart nearly square, or in the lower forms tubular. 

 Often a distinct metamorphosis. Sexes distinct, except in a few cases 

 {certain barnacles, etc). 



Order 1. Cirri/pedia. — Sessile often retrograded ; antennse not devel- 

 oped, living parasitically, the appendages of tbe head some, 

 times formino; net-like organs. Young hatched in the nau- 

 plius state. Suborder 1. — Rhizocephala (Sacculina, Pelto- 

 gaster). Suborder 3. — Genuine Cirripedia (Balanus, Lepas.) 



Order 2. Entomostraea. — A ceplialo-thorax developed ; mandibles and 

 three pairs of maxillae ; five pairs of thoracic feet, no ab- 

 dominal feet ; witliout any gills. The parasitic forms more 

 or less modified in shape, with sucking mouih-parts ; all 

 the young of the nauplius form. Suborder 1. Copepoda 

 (Cyclops). Suborder 2. Siphonostoma (Lerniea, Caligus, and 

 Argulus). 



Order 3. BrancMopoda. Thoracic feet leaf-like ; one to three pairs of 

 maxillae ; number of body-segments varying from a few to 

 sixty ; cephalo-thoras often well developed, and forming a 

 bivalved shell. Young usually a Nauplius. Suborder 1. 

 Ostrncoda (Cypris). Suborder 2. Cladocera (Daphnia). Sub- 

 order 3. PhyUopoda (Limnadia, Apus, Branchipus, and Ar- 

 temia.) 



Order 4. Edriopthalma. — No cephalothorax, thoracic segments dis- 

 tin. t ; respiration often carried on by the abdominal feet. 

 Suborder 1. Isopoda (Idotaea, Asellus). Suborder 3. Am- 

 phipoda (Gauimarus). 



Order 5. PhyUocarida. — Body compressed; rostrum distinct from the 

 carapace ; thoracic feet leaf-like ; no metamorphosis. (Ne- 

 balia.) 



Order 6. Thoracostraca. — Cephalothorax well marked, abdomen often 

 bent beneath the cephalothorax; breathing by gills attached 

 to the maxillipedes and legs. Heart often nearly pentagonal. 

 Usually a well-marked metamorphosis ; young called a 

 Zoea. Suborder 1. C«mac«a (Cuma). ^\x\>OTAer%. 8ync((iida 

 (Acanthotelson). Suborder 3. Slomapoda (Squilla). Sub- 

 order 4. Schizopoda (Mysis). Suborder 5. Decapoda (Cran- 

 gon, Astacus, Homarus, Cancer). 



