Hector F. E. JuNCERser*: Chordeuma obesum, a new Parasitic Copepod. 5 



Chordeuma obesum. The body is composed of a head (ce, cephalon), four thoracic 

 segments (thj — thj and an unsegmented abdomen (g, ap) (postabdomen). The head- 

 region carries three pairs of appendages: antennules (a,), antennæ (aj) and inaxillæ 

 (mx); every trace of mandibles and maxillulæ as well of eyes is wanting. That 

 my explanation of the appendages present is the correct one will be proved by the 

 developmental stages described below sub II. 



The antennules (a,) are situated in front and somewhat ventrally on the rounded 

 head; they are short, clnmsy and unsegmented, ovoid with two blunt terminal pro- 

 cesses and a smaller ventro-lateral spine nearer the base. On the ventral side of the 

 head, far behind the antennules, immediately in front of the upper Up of the mouth 

 (ul), and close together, are a pair of slender papilliform appendages (aj), aJso un- 

 segmented; the development shows that they are the antennæ; and besides there 

 seem to be rudiments of an antennal gland present at the base (if functional appoars 

 doubtful, as I have not been able to fmd an excretory pore). The distal slender, 

 finger-like part of the antenna is clad with delicate adpressed hairs (at all events in 

 unripe specimens). The mouth-opening is protected in front by a small rounded 

 upper lip (ul), and close behind the mouth are the maxillæ (mx), proportionally 

 strong and with their bases almost meeting in the ventral middle line. Theso are the 

 largest and the only segmented appendages of the whole body, consisting of three segments, 

 the terminal one forming a curved claw. The inrier side of the lai^e basal and 

 middle segments, and the front side of the latter and of the claw are provided with 

 similar spines and bristles as in the male (comp. the description of the latter and 

 Fig. 12); the concave ventral side of the claw also carries a single large bristle. 



Each of the four thoracic segments (th, — th^) has a pair of short, conical, unseg- 

 mented feet, (p, — p^) looking almost like parapodia and set rather far apart; distally 

 they often are curved like a (weak) claw, and in unripe individuals this terminal part 

 is sparsely beset \\ith short hairs (PI. II, Fig. 25). The anterior pair are somewhat 

 smaller and weaker than the rest, the posterior generally largest and strongt'st. Each 

 foot represents the stem and outer branch of the typical Copepod-swimming-foot, as 

 shown by the larva, and by the faet that often — and quite regularly in young 

 immature specimens — a papilliform ni(lim«'nt of an inner branch (i) may be seen 

 on tho second, third or fourth pair (PI. I, Figs. .'J, 6 i and PI. II, Fig. 25 i). 



The two posterior thoracic segments (thj, thj) are shorter and narrower Ihan the 

 anterior, from which they are divided by a deep constriction, the latter as it were 

 more joining the head, the former the abdomen. In this constriction lits tightly the 

 menibranous wall of the gall: thus two comparlments of the capsule are formod, the 

 posterior containing the liin<l'r part of tho femalo nnd its f>j;i'-ii> i-< an. I in most 

 cases a male. 



