биота российских вод японского моря - Materials of Alexey Shipunov

8. Genus Exacanthomysis Holmquist, 1981Type species: Acanthomysis davisi Banner, 1948.Carapace anteriorly produced into pointed triangular rostral plate. Labrum withrelatively long anterior spiniform process. Antennal scale lanceolate, with roundedapex, setose all along length of margins; subapical suture present. Marsupium composedof 2 pairs of well-developed oostegites. Tergites of free thoracic segments andof all abdominal segments with 2–3, occasionally with 4 transverse dorsolateral furrows,in some specimens breaking dorsally. First to third and fifth male pleopods andall female pleopods uniramous, reduced to unsegmented plate. Fourth pleopod of malebiramous, relatively short; endopod at least half as long as exopod; exopod 2-segmented; proximal segment straight, with one small and one large simple setae ondistal corners or sometimes without them; distal segment with one very small seta orwithout it and with two strong subequal terminal setae. Endopod of uropod with relativelyshort row of spines on ventral surface between inner margin and statocyst. Telsonelongate, triangular; lateral margins with numerous spines, grouped on distal 1/2–2/3 of these margins: each large spine followed by one or several smaller spines.Remarks. Making morphological analysis of the species belonging formerly tothe genus Acanthomysis, Holmquist (1981a, b) did not manage to define a genus for A.stelleri and A. borealis due to the poor condition of available specimens. Besides, thespecimens, which she had in her disposal, identified by Derjavin as A. stelleri, provedto be A. borealis. It has been determined now based on rather sizeable collections (20samples, 268 specimens of A. stelleri and 35 samples, 662 specimens of A. borealis)that these species agree with the diagnosis of the genus Exacanthomysis and may beincluded in it. The only different character in A. borealis is the apex of the telson,which is not narrowly truncated as in the other related species, but narrowly rounded.However, it may be considered as a distinguishing character at a species level.KEY TO THE SPECIES OF THE GENUS EXACANTHOMYSIS1(2). Telson elongate, triangular, with slightly truncated apex (pl. XIV, fig. 5) ................................................................................................................. E. stelleri (p. 60)2(1). Telson elongate, triangular, with rounded apex (pl. XV, fig. 5) ............................................................................................................................... E. borealis (p. 61)1. Exacanthomysis stelleri (Derjavin, 1913)(Pl. XIV, figs. 1–5).Derjavin, 1913: 202 (Orientomysis stelleri); Ii, 1936: 589 (Acanthomysis stelleri); Holmquist,1981a: 260 (Exacanthomysis arctopacifica); Murano, 1991: 81–86 (Exacanthomysis japonica).Description. Antennal scale straight, 4–5.7 (in juveniles up to 8.6) times as longas broad. Carpo-propodus of endopod of thoracopods 5–8 with 4–7 subjoints. Exopodof pleopod 4 of male 1.3–3.3 times as long as endopod; basal (proximal) segment ofexopod 3–6 times as long as distal one. Endopod of uropod armed with 4–5 (in juveniles)to 5–11 spines on ventral surface close to statocyst. Telson elongate, triangular,60