CLASSIFICATION OF CRUSTACEA. 305 



Class. I. CRUSTACEA. 



Arthropoda breathing by gills situated on the legs, or respiring through 

 the body-walls. Body in the higher forms divided into two regions, a 

 eeph(do-th»rax and abdomen. Two pairs of antennm ; mandibles usu- 

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

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

 (certain barnacles, etc.). 



Order 1. Cirripedia. — Sessile often retrograded; antennae not devel- 

 oped, living parasitically, the appendages of tUe head some- 

 times forming net-like organs. Young hatched in the nau- 

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

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



Order 3. Entomostraea. — A cephalo-thorax developed ; mandibles and 

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

 dominal feet ; without any gills. The parasitic forms more 

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

 the young of the nauplius form. Suborder 1. Copepoda 

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

 Argulus). 



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

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

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

 bivalved shell. Young usually a Nauplius. Suborder 1, 

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

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

 temia.) 



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

 tinct ; respiration often carried on by the abdominal feet. 

 Suborder 1. Isopoda (Idotaea, Asellus). Suborder 2. Am- 

 phipoda (Qammarus). 



Orders. PhyUocarida. — Body compressed; rostrum distinct from the 

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

 balia.) 



Ordar 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. Oumacea (Cuma). Suborder 3. Syncarlda 

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

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

 gon, Astacus, Homarus, Cancer). 



