15 



head, and a complete absence of antennae II in females; a monotypic 

 family, Lycaeopsidae, has been identified. 



The diversity in moq^hological structures of the various groups of 

 Hyperiidea compels us to think that they are not a natural, monophyletic 

 group, but include progenies of various ancestral forms which changed 

 over to a pelagic habitat due to commensalism or parasitism on gelatinous 

 macrozooplankton, mostly coelenterates and tunicates. Pirlot held the most 

 extreme viewpoint in this regard, considering the suborder Hyperiidea to 

 include at least eight, may be even ten, phylogenetically disparate groups, 

 each of which arose from a separate taxon of Gammaridea (Pirlot, 1932). 



Actually, hyperiideans do not have even a single distinct morpho- 

 logical character which is not found in some groups of Gammaridea. Most 

 common features combining hyperiideans can be explained, at best, by con- 

 vergence during adaptation to ectoparasitism or commensalism on medusae 

 and siphonophores rather than historic commonality of their origin. 



Let us consider from this viewpoint some basic morphological char- 

 acteristics of hyperiideans. 



The short antennae I, lacking an accessory flagellum, are typical of 

 23 several families and genera of gammarideans, for .example, the family 

 Talitridae, some genera of the Lysianassidae from the Paracyphocaris- 

 group, and many others. In these groups not only the accessory flagellum, 

 but even the distal articles of the main flagellum are reduced, while 

 the proximal article is highly enlarged, possibly due to oligomerization, 

 which is typical also in hyperiideans. 



Reduction of maxillipeds, loss of their palp, and fusion of the inner 

 lobes: in many genera of gammarideans from different families, we 

 observe a reduction of the maxilliped palp, the reduction being extreme in 

 semi-parasitic or parasitic genera. Thus, in the Paracyphocaris the max- 

 illiped palp is one-segmented, while in the Chevreuxiella and Danaella 

 (family Lysianassidae) and in some other groups, it is totally lacking. The 

 inner lobes of the maxillipeds in some parasitic genera of gammarideans 

 are fused. Simultaneously with a reduction of mouthparts, gammarideans 

 lose their ornamentation on these parts. Probably, this adaptive character 

 is also linked with parasitism on animals with gelatinous tissues. Hence 

 this cannot prove the phylogeny of different hyperiidean groups. 



The reduction of other mouthparts (mandibles, maxillae I and II) 

 in hyperiideans is also completely analogous to some gammarideans 

 changing over to a semiparasitic mode of life. These examples have 

 been examined in detail by Pirlot (1931). 



Parallel with the reduction of mouthparts in many genera of gam- 

 marideans, there is a structural simplification of the telson (it becomes 

 entire) and the 2nd exopodite article of uropods III disappears. As men- 

 tioned above, these characters are also essential for all hyperiideans. 



