146 



THE CRUSTACEA 



pre-coxa, nine segments in 

 dact- - 



en.-< 



according to Hansen, a pre-coxal segment (pleuropodite of Coutiere) 

 which is distinct only in the Leptostraca and Stomatopoda. The . 

 axis of the limb is continued by the endopodite \rhich forms an 

 ambulatory leg, while the flagelliform exopodite is used for 

 swimming. There are hve segments in the endopodite, termed 

 by Milne - Edwards respectively the ischiopodite, meropodite, 

 carpopodite, propodite, and dactylopodite (often abbreviated to 

 ischium, merus, carpus, propodus, and dactylus). Hansen con- 

 siders that the terminal claw which is sometimes distinct from the 

 dactylopodite represents an additional segment, making, with the 



the axis of the limb instead of the 

 seven usually recognised. It seems 

 probable, however, that this claw 

 (termed stylopodite by Coutiere) is 

 simply an enlarged spine and not 

 one of the segments of the limb. 



At the bases of the thoracic 

 limbs on the outer side are a series 

 of epipodial appendages (exites) 

 probably originally branchial in 

 function. It is not quite clear how 

 many of these appendages must be 

 attributed to each thoracic limb of 

 the primitive type, but probably at 

 least two are to be recognised, an 

 e^ipoclite attached to the coxopodite 

 and a inoepipodite to the pre-coxal 

 segment. The oostegifes, or brood- 

 plates, attached to the inner side of 

 the coxopodite in the female sex in 

 some of the orders, and forming a pouch for the protection of the 

 eggs and young, may possibly be derived from some of these epi- 

 podial structures, as Claus suggests. The terminology ap])lied to the 

 thoracic limbs in systematic works differs greatly in the various orders 

 of Malacostraca. From one to three of the anterior pairs ma}^ be 

 called maxillipeds, the second and third pairs are in some cases known 

 as gnathopods, and the last five pairs are often termed peraeopods. I 



The abdominal appendages are all biramous and are used in 

 swimming, but the sixth pair differ in form and function from the 

 others. The first five pairs are known as j^leo^xids. They have the 

 protopodite composed of two segments (occasionally there are 

 traces of a third), and the rami are fringed with long setae and 

 assist the thoracic exopodites in the ordinary swimming move- 

 ments of the animal. The appendages of each pair are coupled 

 together by a group of hooked spines (retinacula) cither on the 

 inner edge of the protopodite or on a special process of the 



Fig. 8G. 



Diasram of a Malacostracan thoracic 

 appendage, hs, basipodite ; carp, carpo- 

 podite; ex, coxopodite; dact, dactylopodite; 

 en, endopodite ; ep, epipodites ; ex, exopo- 

 dite ; isoh, ischiopodite ; me.r, meropodite ; 

 prop, propodite ; proi, protopodite. 



