Sub-Class 2. Malacostraca. Order 1. Ewpliausiacea. 211 



are locomotor : each consists of a seven-jointed, long and thin 

 endopod, and a strong exopod, fringed with setee, and serving 

 as a natatory organ : there is also an e p i p o d which is much-branched, 

 except in the case of the first pair, and haags free on the side of the 

 animal, acting as a gill. Byes, antennae, carapace, abdomen, and 

 swimmerets are like those of the Prawn [q.v.). The Euphausiacea are 



Fig. 172. Tkysanopus tricitspidatus. 1 — 7 first and seventh abdominal segments ; 

 A^ — Ar, first and second antenna; H3 third abdominal appendage: K^, K^, Kj first, 

 second, and seventh thoracic limbs ; K^ex and K^ex exopod of the third and eighth thoracic 

 limbs ; ep epipod of the eighth thoracic limb ; L phosphorescent organ ; S carapace. — After 

 Sars. 



also characterised by the retention of the nauplius eye throughout 

 life J the possession of peculiar eye-like phosphorescent 

 organs on the eye-stalk, on the basal joint of the second and 

 seventh thoracic limbs, and on the ventral side of the first four 

 abdominal somites ; and by hatching as free-swimming n a u p 1 i i . 

 The order, which is relatively poor in species, is represented both 

 in warm and in cold seas {Thysanopus, Euphausia, etc.) ; some 

 species form an important part of the food of the Whale-bone 

 Whale. 



Order 2. Mysidacea. 



Thia order is divided into two groups, the true Mysidse and tlie 

 LopliogastridBB, wMcli latter group is confined to great depths, and 

 comprises many curious and abeiTant forms. The folio-wing account refers only 

 to the true Mysidse. 



The general appearance of the Mysidas, as of the Euphausiacea, is 

 prawn-like. The body is, however, less compressed and more 

 rounded, and the abdomen does not exhibit the very obvious bend of 

 the Prawns (and Euphauda) . Each of the thoracic limbs is furnished 



p 2 



