308 



PHYLUM ARTHROPODA. 



Series II. Eumalacostraca. 



Division I. Syncarida, the order Anaspidacea, primitive fresh- watei 

 forms, without a carapace ; with the eight thoracic segments all 

 distinct (Anaspides]^ or with the first one fixed to the head (Koonunga) ; 

 with stalked eyes in Anaspides, sessile eyes in Koonunga ; with 

 lamellar branchiae on the thoracic legs, whose slender exopodites are 

 also respiratory. 



Division 2. Peracarida, with a carapace that leaves at least four of 

 the thoracic segments free, with the first thoracic segment always fused 

 to the head, with usually sessile eyes, with a brood -pouch on the 

 thoracic appendages of the female, with an elongated heart, with 

 direct development. Numerous orders including : the pelagic M^si- 

 dacea (formerly united with Euphausiacea 

 as Schizopods), e.g. My sis \ the pelagic 

 and deep-water Cumacea, e.g. Cuma and 

 Diastylis ; the Isopods, with dorso-ventral 

 flattening of the body, a posterior heart, 

 and respiratory organs on the abdominal 

 limbs, e.g. the terrestrial wood-lice (For- 

 celliO) Oniscus, etc.), which show minute 

 trachea-like respiratory tubes in the abdom- 

 inal limbs, and corresponding forms on the 

 shore (e.g. Ligia, Idotea] ; the Amphipods, 

 with lateral flattening of the body, an 

 anterior heart, and respiratory organs 

 usually on the thoracic limbs, e.g. Gam- 

 marus locusta in the shore pools, G. pulex 

 in fresh water, and sandhoppers like 

 Talitrus and Orchestia ; the * * no body " 

 crabs, Caprella ; Phronima^ living inside 

 the glassy case of the free-swimming 

 Tunicate Pyrosoma. 



Division 3. Hoplocarida, with a carapace 

 at leayes at ^ four of the fa 



segments free, with stalked eyes, with the 



, 

 FIG. i62.-An Amphipod 



(Caprella Imeans). 



The two anterior thoracic seg- eggs carried in a chamber formed by the 

 ments are fused to the head ; max iiii pe des, with an elongated heart, 

 the abdomen is greatly re- , f . . j & 



duced and without append- and with a complicated metamorphosis. 

 ages ; the fourth and fifth Order : Stomatopods, e.g. Squilla, with 

 thoracic segments bear only t h e sec ond maxiiiipedes forming very large 

 respiratory plates. raptorial organs. 



Division 4. Eucarida, with a cephalo - thoracic shield uniting the 



head and thorax segments ; with stalked eyes ; with a saccular heart ; 



with eggs attached to the abdominal endopodites ; with spherical 



spermatozoa showing peculiar radiating pseudopodia ; usually with a 



complex metamorphosis. 



Order I. Euphausiacea : shrimp-like surface and deep-water forms, 



with biramous thoracic limbs as in Mysids, e.g. Euphausia. 



Order 2. Decapoda : with the three anterior thoracic limbs 



turned forward as maxiiiipedes, with the other thoracic limbs almost 



always uniramous. 



