Lophogaster japonicus W. M. Tattersall, 1951

Lophogaster japonicus W. M. Tattersall, 1951 View in CoL

( Figs. 2 View Fig , 3 View Fig )

Lophogaster typicus View in CoL : Ortmann, 1906: 23 (in part, not M. Sars, 1857).

Lophogaster japonicus W. M. Tattersall, 1951: 19 View in CoL , figs. 1b, 2a; Murano, 1970: 3, fig. 1a–d; Saitoh and Kajihara, 2002, figs. 2a, 3; Fukuoka, 2009: 406.

Lophogaster pacificus View in CoL : O. S. Tattersall, 1960: 534, fig. 3; Băcescu, 1981: 265, figs. 1c–i, 2a–i; — 1991: 88 (at least in part, not Fage, 1942).

Material examined. West Pacific. North-eastern Japan: off Kesen-numa ; 2 males (cl 7.0, 7.0mm), 1 ovig. female (cl 7.7 mm), 38°29.8′N 141°41.0′E, 144–0 m, 25 Apr 1964, coll. M. Murano (NSMT-Cr 32875). Central GoogleMaps Japan: off

Kashima; 5 ovig. females (cl 7.2–8.0 mm), 37°40′N, 141°05′E, 28– 27 m, trawl, 24 Nov 1991, coll M. Tanno (NSMT-Cr 32876): Suruga

Bay; 1 juv. (cl 2.6 mm), KT-65-9, St. 111-1, 34°30.1′N 138°30.5′E – 34°31.2′N 138°33.7′E, 1000–0 m, ORI net, 24 Apr 1965, coll. M. Murano (NSMT-Cr 32877) GoogleMaps ; — 1 juv. (cl 3.2 mm), KT-69-6, St. 391-1, 34°54.3′N 138°27.8′E – 34°54.2′N 138°27.1′E, 66– 42 m, bottom-net, 13 May 1969, coll. M. Murano (NSMT-Cr 32878); — 1 male (cl 3.2 mm), 12 juvs (cl 1.7–2.8 mm), KT-69-6, St. 392-1, 34°54.0′N 138°27.0′E – 34°54.1′N 138°26.3′E, 72 m, bottom-net, 13 May 1969, coll. M. Murano (NSMT-Cr 32879):

Suruga Bay , off Toi; 2 males (3.5, 4.2 mm), KT-78-18, St. OT-7, 160– 145 m, 2 m Beam Trawl , 20 Nov 1978, coll. M. Murano (NSMT-Cr 32880): — Sagami Bay ; 1 ovig. female (cl 7.0 mm), l Shinyo-Maru z, St. 2, 34°31.35′N 139°25.39′E, 126– 121 m, dredge, 17 Oct 1991, coll. M. Murano (NSMT-Cr 32881) GoogleMaps .

Diagnosis. Integument of body ( Fig. 2 View Fig ) somewhat calcified.

Carapace ( Figs. 2 View Fig , 3a–c View Fig ) with small tubercles or processes of different sizes and shapes scattered on dorsal and dorso-lateral surfaces; stout post-orbital processes present and median dorsal carina marked on posterior part; rostral plate wide, completely covering eye-stalks as well as basal 2 segments of antennular peduncle, antero-lateral part with short but distinct tooth; rostral process rather long with slightly upturned apex extending beyond antennular lamina and/or barely reaching tip of antennal scale; postero-lateral part with short tooth (alar spine) directed obliquely upwards, sometimes very feebly toothed or rarely indistinct.

Abdomen ( Fig. 2 View Fig ) in both sexes with sharp ventral median tooth on anterior 5 somites, among which second one is strongest, then decreasing its height posteriorly; pleuron of fifth somite ending in small postero-ventral tooth; sixth somite about 1.5 times as long as fifth, its ventral margin with strong tooth at mid-length as in postero-ventral part.

Telson ( Figs. 2 View Fig , 3d, e View Fig ) about twice length of sixth abdominal somite, marked median dorsal tubercle present on basal part, dorsal surface slightly sulcate; lateral margin commonly with 2, rarely single, pairs of setal-spines; posterior margin with orginal 2 pairs of strong setal-spines; distal lamina between strong terminal setal-spines less produced but broad, bearing 8 small setal-spines and 1 pair of long plumose setae.

Exopod of uropod ( Figs. 2 View Fig , 3d, e View Fig ) slightly shorter than endopod, outer margin smooth and naked, ending in tiny process; endopod extending well beyond posterior lateral setal-spines of telson.

Antennular lamina ( Fig. 3f View Fig ) with anterior margin providing short projection in median part together with widely rounded major projection, thus forming convexity and 1 long seta arising from concaved part between small and large projections.

Antennal scale ( Fig. 3 g View Fig ) sub-triangular in general shape, about 1.5 times as long as broad, with strong distal tooth slightly curving inwards, and weakly convex outer margin bearing 2 or 3 obtuse denticles on anterior half.

Remarks. Tattersall (1960) considered that Lophogaster japonicus could be a junior synonym of L. pacificus . Contrary to this, Murano (1970) pointed out that L. japonicus is a good species, and it can be distinguishable from L. pacificus in the shapes of the antennular lamina, antennal scale, and rostral length.

In addition to these points, as briefly noted by Murano (1970), L. japonicus has a relatively short uropod and the carapace is armed with slightly low and obtuse tubercles when compared with those of L. pacificus . Unfortunately, Băcescu (1981, 1985, 1991) was unaware about the paper by Murano (1970), while Casanova (1996) regarded L. japonicus to be a valid species.

Although L. japonicus is little-known for its morphological features, this species is remarkable among the members within the genus in having a sub-triangular antennal scale with two or three obtuse denticles on its outer margin. In addition, this species is characterised by having a combination of following features: antennular lamina with anterior margin with widely rounded major protrusion together with inner short projection; carapace with post-ocular process and numerous tubercles on dorsal surface as well as somewhat short postero-lateral spine; telson with one or two pairs of setal-spines on its lateral margin.

One ovigerous female (NSMT-Cr 32881) and small specimens (NSMT-Cr 32877, -32878) devoid of a marked postero-lateral carapace tooth (alar spine); nevertheless other features agreed well with those of this species.

Distribution. This species is recorded with certainty from the western North Pacific, and commonly captured off the Pacific coasts of Japan, and in depths from 50–300m (W. M. Tattersall, 1951; Murano, 1970; Saitoh and Kajihara, 2002; Fukuoka, 2009).