CHAPTER XIII 



THE AMPHIPODA 



Order AmpMpoda, Latreille (181G). 



Sub-Order 1. Gammaridea. 

 ,, 2. Hyperiidea. 



„ 3. Caprellidea. 



„ 4. Ingolfiellidea. 



Definition. — Peracarida in which there is no distinct carapace, 

 but the first thoi'acic somite (more rarely also the second) is 

 coalesced with the head ; the telson is usually distinct from the 

 last somite ; eyes sessile ; antennules often biramous ; antennae 

 without exopodite, the peduncle typically of five segments ; 

 thoracic limbs without exopodites ; first pair modified as maxil- 

 lipeds, coalesced at the base, without epipodite ; remaining pairs 

 variously modified, the second and third commonly prehensile, 

 coxopodites always short, usually expanded as coxal plates, 

 movably connected with the body ; branchial appendages on inner 

 side of coxopodites of some of the thoracic limbs ; pleopods, when 

 fully developed, divided into two sets, the first three pairs with 

 tnultiarticulate rami, the last two pairs generally similar to the 

 uropods, with unsegmented rami ; no sexual modification of pleo- 

 pods ; the young leave the brood-pouch provided with all the 

 appendages of the adult. 



Historical. — In establishing the order Amphipoda (1816) 

 Latreille excluded from it the genus Cijamus, which he referred to 

 the Isopoda. Later, he established a separate order, Laemodipoda, 

 for Caprella and Ci/amus, placing it between the Amphipoda and 

 Isopoda. This arrangement was adopted by H. Milne-Edwards, 

 who further divided the Amphipoda into two families, Gammarina 

 and Hyperina. Kroyer, in 1843, showed very clearly that the 

 Laemodipoda present only an extreme modification of the Amphi- 

 pod type. Dana, in 1852, subdivided the Order into three groups 

 — Caprellidea, Gammaridea, and Hyperiidea, a classification which 

 has held its own to the present time. There appear to be no 

 sufficient grounds for establishing the additional divisions of 



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