LYCAEIDAE Claus, 1879

Zeidler, Wolfgang, 2016, A review of the families and genera of the superfamily PLATYSCELOIDEA Bowman & Gruner, 1973 (Crustacea: Amphipoda: Hyperiidea), together with keys to the families, genera and species, Zootaxa 4192 (1), pp. 1-136 : 47-48

Family LYCAEIDAE Claus, 1879

Diagnosis. Body length 5–10 mm, with slightly inflated pereon, especially in females. Head of females rounded, relatively large; slightly smaller in males but also rounded ( Lycaea ) or slightly pointed ( Simorhynchotus ); as long as first 3–5 pereonites. Eyes large, occupying most of head surface. Antennae 1 of females with 2-articulate peduncle, and enlarged first flagellar article (callynophore), followed by two small, terminal articles. Antennae 1 of males with 2-articulate peduncle, and enlarged, curved first flagellar article (callynophore) with two-field brush of aesthetascs medially, and three smaller, slender articles inserted on, or near, antero-distal corner. Antennae 2 absent in females. Antennae 2 of males with relatively short, slightly enlarged basal article, three slender articles folded back on one another and one short terminal article, tucked underneath head and pereon. Mandibles with 3- articulated palp in males, absent in females. Maxillae 1 very reduced in size, consisting of tiny rounded lobes, or absent. Maxillae 2 absent. Gnathopoda simple, weakly chelate or sub-chelate. Pereopod 5 the longest. Pereopods 5 & 6 with moderately enlarged basis, distinctly shorter than remaining articles combined, which are inserted terminally. Pereopod 7 reduced in size, but with full complement of articles, with enlarged basis, which is longer than remaining articles combined. Uropod 1 with articulated endopoda and exopoda. Uropod 2; endopod sometimes fused with peduncle. Uropod 3; endopod always fused with peduncle. Telson triangular, with rounded apex, usually extending to near limit of U3, fused with double urosomite. Gills with folds on pereonites 2–6. Oostegites on pereonites 2–5.

Genera. Lycaea Dana, 1852 and Simorhynchotus Stebbing, 1888 .

Remarks. The systematic limits of this family are in a state of flux, with some authors including such diverse genera as Pseudolycaea (= Lycaea ), Tryphana , Brachyscelus and Thamneus , besides Lycaea (e.g. Bowman & Gruner 1973, Shih & Chen 1995). Authors who have accepted this arrangement usually place Simorhynchotus in the family Oxycephalidae , based on the erroneous assumption that the maxillae are present in Lycaeidae and absent in Oxycephalidae and Simorhynchotus . While the maxillae are not discernible in Simorhynchotus , this is also only true for two genera of Oxycephalidae ; Oxycephalus and Rhabdosoma . In all other genera of Oxycephalidae , the first maxillae are reduced to a small rounded lobe, and the second maxillae are absent, or so reduced that they cannot be distinguished from the buccal mass, as found in Brachyscelus and Lycaea . Thus, there is no valid reason to include Simorhynchotus in the family Oxycephalidae based on the absence of maxillae. In Thamneus the maxillae are present as small rounded lobes and in Tryphana the maxillae are relatively well developed.

Thus, in this review, the family Lycaeidae is restricted to the genera Lycaea and Simorhynchotus . Simorhynchotus more closely resembles Lycaea , rather than any genus of Oxycephalidae , in the general habit and the morphology of the second antennae of males, and the gnathopoda, pereopoda, urosome and coxae. Also, in both Lycaea and Simorhynchotus , the second antennae of males extend posteriorly for the entire length of the pereon. In Oxycephalidae the second antennae of males usually extend posteriorly to about pereonite 2, and only in Tullbergella do they extend beyond pereonite 2, to about pereonite 5. Similarly, in other families of Platysceloidea the second antennae of males do not extend posteriorly much further than about pereonite 2, except for some genera of Platyscelidae and Parascelidae where they can extend to pereonite 3 or 4.

Justification for the removal of Brachyscelus , Thamneus and Tryphana from Lycaeidae is presented under the respective families Brachyscelidae , Thamneidae fam. nov. and Tryphanidae .

Clearly the family Lycaeidae is most closely related to Oxycephalidae , and this is supported by the phylogenetic analysis ( Figs 1 & 2). Browne et al. (2007) and Hurt et al. (2013) also found strong support for the inclusion of Lycaea within the Oxycephalidae .

Figures

FIGURE 1. Phylogenetic analysis of the genera of the superfamily Platysceloidea. One of three equally most parsimonious trees derived from a PAUP 4.0 analysis of the DELTA data base; length 275 steps, consistency index = 0.5164, rescaled consistency index = 0.3476. Branches are marked with the number of character changes. Vibilia is used as the out-group.