Comments on the Newly Proposed Gammaridean Amphipod Families Crangonycidae and Melitidae

COMMENTS ON THE NEWLY PROPOSED GAMMARIDEAN AMPHIPOD FAMILIES CRANGONYCIDAE AND MELITIDAE

JOHN R. HOLSINGER Department of Biology, Old Dominion University, Norfolk, Virginia 23508, U.S.A.

Bousfield (1973), in his recent book entitled "Shallow-water Gammaridean Amphipoda of New England", has elevated the Crangonyx group to the family Crangonycidae and the melitids to the family Melitidae. The division of the heterogeneous and widely distributed family Gammaridae into separate families that more clearly reflect evolutionary phylogenies and delineate natural groups is certainly justified. However, in view of the many unresolved taxonomic and zoogeography problems within the Gammaridae and especially within the generic clusters making up the crangonycids and the melitids, the erection of the new families Crangonycidae and Melitidae seems to me to be premature. The three or four of us (M. Straškraba and myself in particular) who are currently working on genera and species in the Crangonyx group on a world-wide basis have still failed to reach agreement on precisely how to define this group, much less elevate it to familial level. Moreover, the taxonomic status of the melitids (roughly equivalent to the Hadzia group; see Holsinger & Minckley, 1 97 1 ) is also in a state of flux. In my opinion, the most acceptable approach to the subdivision of Gammaridae would be to treat newly established families on a cosmopolitan basis, considering all potential genera, their morphological affinities, distributional patterns, etc., inste4d of choosing only a few examples from a narrowly defined geographical region and basing whole new taxa on them. The elevation of the Crangonyx group, an exclusively freshwater group of amphipods, to the familial level seems out of place in a guidebook devoted almost entirely to marine and brackish water amphipods of the New England region. This is especially germane when one considers the fact that only three species in the Crangonyx group occur in the geographical region covered and are, at best, only peripheral to the New England coastal area. Similarly, placing the melitids, which is mostly a warm temperate and tropical group, in a separate family on the basis of a few representative forms from the New England region seems presumptuous in a guidebook devoted to essentially "cold" temperate zone amphipods. The erection of Crangonycidae should have logically included consideration of the east Asian genera Eocrangonyx and P.reudocrangonyx, combined with a 317 definitive stand on the status of the Southern Hemisphere genera previously assigned to the Crangonyx group and including Au.rtroniphargu.r, Hurleya, Para- ci,angonyx, Protocrangon yx, and Sternophysinx (see Holsinger & Straškraba, 1973). The separation of the crangonycids and the melitids from the Gammari- dae also poses the problem of what to do with the Niphargus group, the bogi- diellids, and aberrant subterranean genera such as Allocrangonyx, Kerguelenella, Metacrangonyx, Psettdocrangonyx, and Salentinella. A more complete examination of the melitids should have included consideration of the genera Eriopi.ra, Eriopi.rella, Paraniphargiis, and P.rammoni?hargu.r. Five of the 12 genera listed by Bousfield (1973: 61) as components of the new family Melitidae have been previously assigned to the Hadzia group by several workers and a diagnosis of this group is essentially that of Melitidae. Actually, Hadziidae has already been used as a family name for this group of amphipods (see Ruffo, 1947), although it has been discarded in subsequent papers by that worker. Both the diagnoses of the families Crangonycidae and Melitidae contain errors and omissions and fail to cover many of the genera intended for inclusion in these groups. For example, ApoC1angonyx, which has always been regarded as a member of the Crangonyx group (Holsinger, 1969), was omitted from the list of North American genera enumerated by Bousfield as belonging to the Crangonycidae. Ironically, Allocrcmgonyx, an aberrant genus that was removed from the Crangonyx group by Holsinger ( 1971) , was included as a member of the new family. Under component tropical American genera of Melitidae listed by Bousfield, the genus Mexiweckelia was omitted and the now generally accepted synonymy of Metaniphargus with Hadzia was not mentioned. Moreover, if one strictly applies the diagnosis of Melitidae given by Bousfield concerning the number of apical spine teeth (sic) on the outer plate of the first maxilla, three of his component genera (viz. Metai7lphai,gu,i-, Parall'eckeliä and Itleck.elia) would be excluded.

Although I am basically in agreement with Bousfield that the current concept of the family Gammaridae (s. lat.) may be unrealistic and that amphipod systematics would be improved by subdivision of this family into smaller, more natural units, I find it difficult to accept his newly proposed families until some of the included taxa are more clearly defined and the problems discussed above are resolved. LITERATURECITED BOUSFIELD,E. L., 1973. Shallow-water gammaridean Amphipoda of New England: 1-312. (Cornell University Press). HOLSINGER,J. R., 1969. The systematics of the North American subterranean amphipod genus Apocrangonyx (Gammaridae), with remarks on ecology and zoogeography. Amer. Midland Natural., 81 (1): 1-28. -, 1971. A new species of the subterranean amphipod genus Allocrangonyx (Gammaridae), with a redescription of the genus and remarks on its zoogeoraphy. Int. Journ. Speleol., 3: 317-331, 7 plates.