NO. 1101. PARASITIC C0PEP0D8— CALK 1 IDJ:— WILSON. 509 



SIT.MMARY. 



1. Tlio lK)d_y of the Caligids hori^ tliscusscHl is made \\\) of three ])arts 

 or regions — a cephak)-thorax covered with a e!ii'a])aee, a free thorax of 

 two segnients the posterior of which is the o-enital seginent, and an 

 abdomen of from one to four segments. 



2. The cephah)n bears seven pairs of appendages, namely: Two pairs 

 of antenna% one pair of mandibles, two pairs of maxilhe, and two pairs 

 of maxillipeds. Each of the five thorax segments carries a single pair 

 of swimming legs, those on the lifth segment being rudimentary in 

 all the genera, while the fourth pair are also rudimentary in Alchion 

 and Pseudocaligus. The abdomen has no appendages, but carries at 

 its posterior end the paired anal laminjv. 



3. The carapace is oval or elliptical. Articulated with its anterior 

 margin are the frontal plates or modified basal joints of the first 

 antennte. In six of the genera — Caligus^ PmiidocaJlgus^ Caligodcs, 

 Sy)iexf/ux, Jloiiiototes^ and Jkrapetfdus — these frontal plates are pro- 

 vided with lunules or sucking disks. The carapace is divided by 

 grooves or sutures into four areas — the cephalic, the thoracic, and the 

 right and left lateral areas — the principal grooves ])eing arranged in 

 the shape of the letter H. The posterior part of the body is usually 

 much narrower than the carapace. 



4. The first antenna are ver}' fulh* innervated, and thus t>econu' 

 highly sensitive. The second antennty carry hooks or claws on their 

 terminal joints, and are modified into stout prehensile organs, particu- 

 larly large and strong in the male. The first maxillipeds are weak 

 and apparently useless, unless it l)e to keep the mouth parts clean. 

 The second maxillipeds are large and well develo])ed, and, with their 

 terminal claws, form the chief organs of prehension for holding the 

 parasite on its host. 



5. The eyes are simple and paired, l)ut are fused together on the 

 median line instead of being separate, as in the Argulida?. The mouth 

 parts are modified into a proboscis for sucking up the food; the single 

 pair of mandibles are concealed within this proboscis, while the two 

 pairs of maxillae are outside and free from it. The first pair are sim- 

 ple, but rudimentary, and have migrated to a position near the margin 

 of the carapace behind the second antenntie. The second maxillre are 

 simple in those genera which have lunules on the frontal plates, but 

 are bifurcate in the remaining genera. They are situated close to the 

 proboscis on either side. 



6. Situated upon the ventral surface, on the mid line, between the 

 bases of the second maxillipeds and the first swimming legs, is the 

 furca or sternal fork, consisting of a stout chitin plate whose tip is 

 bifid much like an old-fashioned bootjack. It points backward, and its 

 use is prol)ably to prevent the animal from slipping while on its host. 



Proc. N. M. vol. xxviii— 04 33 



