CHAPTER XIII 



THE AMPHIPODA 



Order Amphipoda, Latreille (18 1C). 



Sub-Order 1. Gammaridea. 

 2.. Hyperiidea. 

 3. Caprellidea. 

 4. Ingolfiellidea. 



Definition. Peracarida in which there is no distinct carapace, 

 but the first thoracic 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 

 multiarticulate 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 Cyamus, which he referred to 

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

 for Caprella and Cyamus, 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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