CLASSIFICATION OF CRUSTACEA. 335 



Class. I. CRUSTACEA. 



Artliropodfi, hreathing by gills situated on the legs, or respiring through 

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

 cephalo-thorax and abdomen. Two pairs of antenna! ; 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.). 



Subclass 1. Neocarida. — Genuine Crustacea, with two pairs of anten- 

 nae; biting mouth parts ; mostly modern types. 



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

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

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

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

 gaster). Suborder 2. — Genuine Cirripedia (Balanus, Lepas.) 



Orders. Entomostraca. — A cephalo-thorax developed; mandibles and 

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

 dominal feet ; without any gills. Tbe parasinc forms more 

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

 the young of the nauplius form. Suborder 1. Copepoda 

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

 Argulus). 



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

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

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

 bivalved shell. Young usually a Nauplius. Suborder 1. 

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

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

 temia.) 



Order i:. PhyUocarida. — Body compressed; rostrum distinct from the 

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

 balia.) 



Order 5. — Tetradecapoda. — No cephalo-thorax, thoracic segments dis- 

 tinct ; respiration often carried on by the abdominal feet. 

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

 phipoda (Ganimarus). 



Order 6. Stomapoda. — Abdominal feet respiratory. (Squilla.) 



Order 1. Decapoda. — Cephalo-thorax well marked, abdomen of ten bent 

 beneath the cephalo-thorax ; breathing by gills attached to 

 the maxillipedes and legs. Heart often nearly square. 

 Usually a well-marked metamorphosis ; young called a 



