CRUSTACEA. 539 



A few Amphipoda, Isopoda, and Decapoda are terrestrial. The Branchio- 

 poda are exclusively found in fresh water or in brine : one or two Cirri- 

 pedia occur in brackish waters. Other Cirripedia, like the Leptostraca, 

 Cumacea, and Stomatopoda, are exclusively marine. Representatives of 

 other orders are both marine and fresh water : the majority of Schizopoda 

 and Decapoda however are marine 1 . Several Cirripedia, many Copepoda, 

 and some Isopoda are parasitic. Polymorphism has been observed among 

 male Arthrostraca, principally in Amphipoda. A development of colour in 

 connection with reproductive activity is seen in some Cladocera. Phos- 

 phorescence occurs among marine Copepoda (e. g. Sapphirina\ Ostracoda, 

 and in the Euphausidae among Schizopoda. The majority prey upon 

 animals or plants. The genus Estheria is found in the Devonian strata : 

 other supposed Phyllopoda, e. g. Hymenocaris, from Silurian and Carbon- 

 iferous strata, may be allied to Leptostraca. The shells of Ostracoda occur 

 in most formations. Cirripedia date from the Inferior oolite : Arthrostraca 

 from Devonian strata : Decapoda from the Coal measures. 



The Crustacea may be classified as follows (Claus) : 



A. ENTOMOSTRACA : small, simply organised; number of somites and of 

 appendages very variable. 



1. Phyllopoda : body elongated, generally well segmented, with a shield-shaped 

 or lateral bivalved shell, and at least four pairs of lobed and lamellate natatory feet. 



(a) Branchiopoda, which are large sized ; with well segmented bodies, and 

 10-20 or more feet with well-developed branchiae. Branchipus, Artemia, Apus, 

 Limnetis, Limnadia, Estheria. 



(/3) Cladocera, which are small, laterally compressed with a bivalve shell and 

 large natatory biramose second antennae. Sida, Daphnia, Moina, Bosmina, Poly- 

 phemus, Leptodora, &c. 



2. Ostracoda : small, with unsegmented body ; seven pairs of appendages, and 

 a rudimentary abdomen; all inclosed by a bivalve shell. Cypridina, Cythere, 

 Cypris, &c. 



3. Copepoda : elongated ; generally segmented ; no shell of any kind, and 4-5 

 pairs of biramose thoracic feet ; and five-jointed abdomen. Often parasitic, and 

 then degenerate ; e. g. Cyclops, Chondracanthus, Caligus, Lernaea, Argulus, &c. 



4. Cirripedia : fixed ; body not clearly segmented ; inclosed in a fold of the 

 integument, generally strengthened by calcareous valves; as a rule five pairs of 

 biramose thoracic feet ; hermaphrodite ; e. g. Lepas, Scalpellum, Balanus, Sacculina. 



B. MALACOSTRACA. Head composed of five, thorax of eight, and abdomen 

 of six somites. 



1 A peculiar Ostracode, Elpidium Bromeliarum, has been found by Fritz Miiller in the water 

 retained by the leaves of Bromeliads in Brazil. It is not found in any of the streams, ponds, &c., 

 around. See Nature, xxii. 1880, p. 55. The Amphipod Phronima makes a 'house' for itself out of 

 a Pyrosoma, a Satya % or even the Siphonophoran Abyla (Mayer, Mitth. Zool. Stat. Naples, i. 1879, 

 p. 46). 



