r— r— . * I r^i-^ 



^ I i \ l\ ll ,11 It 



Fig. 2. A. communis: A, first antenna; B, second antenna; C, upper 

 lip; D, lower lip. From Williams (1970). 



Anteriorly, the head bears a pair of short antennae (first antennae or 

 antennules) and a pair of much longer ones (second antennae or, simply, 

 antennae) (Fig. 2A, B) . Ventrally the head bears a mouth which has an 

 upper (or anterior) lip or flap and a bilobed, lower (or posterior) lip 

 (Fig. 2C, D) . Posterior to the mouth is a paired series of small 

 appendages used in feeding; from front to back these are respectively 

 the mandibles, first maxillae (or maxillules) , second maxillae (or, 

 simply, maxillae), and maxillipeds (Fig. 3A-F) . In addition the head 

 has a pair of small eyes; these occur dorsal ly, one on each side 

 (Figs lA, 8B). 



Each segment of the thorax is dorsoventrally flattened and bears lat- 

 erally a leg or peraeopod (pereiopod or pereopod) ; in all there are 

 seven pairs (Fig. lA) . There are some differences in structure between 

 each pair of legs, but these are not great, and only the structure of 

 the first pair of legs of adult males is distinctly different in that 

 the two most distal leg segments are expanded to form a claw-like appa- 

 ratus (Figs 4A,B; 5A-F) . The palm of this usually bears near its mid- 

 point a prominent triangular projection and proximally a few tooth-like 

 setae (Fig. 4A) . Each leg consists of six apparent segments, termed 

 respectively the dactylus, propodus, carpus, merus, ischium and basis 

 of which the dactylus is the most distal. A seventh leg segment, the 



