Amblyops sagamiensis, Murano, 2012

Murano, Masaaki, 2012, The Genus Amblyops (Crustacea: Mysida: Mysidae: Erythropinae) from East Asia and Australia, with Descriptions of Ten New Species, Species Diversity 17 (1), pp. 49-85 : 70-74

Amblyops sagamiensis sp. nov.

(Figs 14–16)

Amblyops sp. 1: Bravo 1996: 38, g. 28.

Type series. H olotype: adult female (15.3 mm), NSMT- Cr 21361, RV “Tansei Maru”, KT-64-17 Cruise, St . 84-3, 35°06 .3′N 139°17.0′E to 35°04 .4′N 139°17 .2′E , Sagami Bay , central Japan, 25 October 1964, 16:34–17:45, ORI net that contacted the sea oor at about 1000 m depth during an oblique haul. Allotype: adult male (without cephalon), NSMT-Cr 21362, same data as holotype . Paratypes: 1 adult female (ca. 17 mm, divided into 2 parts), 3 immature males (ca. 7.6 mm, 1 without abdomen, 1 without cephalothorax), 8 immature females (ca. 13.5, 10.6, 10.3, 8.9 mm, 2 without cephalon, 2 damaged), NSMT-Cr 21363, same data as holotype .

Description.C arapace (Fig. 14A) with broadly rounded anterior margin without de nite rostral projection, leaving most of eyeplates exposed; anterolateral corner rounded; posterior margin emarginate, leaving last thoracic somite exposed dorsally.

Eyes (Fig. 14A–C) plate-like without visual elements, separated from each other, relatively large, extending to posterior margin of second segment of antennular peduncle; each eyeplate quadrangular with rounded corners, wider than long, with many spinules on anterolateral area; lateral margin nearly twice as long as mesial margin; anterior margin very slightly arched, without de nite papilliform projection but slightly upturned knob recognized at outer 1/3.

Antennular peduncle of female (Fig. 14A) somewhat robust; rst segment with anterolateral corner prolonged anteriorly and tipped with several setae; second segment very short; third segment 1.3 times as long as wide, armed with 6 setae along inner margin and several long setae on distomesial margin.

Antennal scale of female (Fig. 14A, D) overreaching anterior margin of antennular peduncle by 2/5 of its length, 3 times as long as wide; outer margin slightly convex, terminating in strong denticle extending slightly beyond apex of blade and armed with subsidiary spinule near basal end of its inner side; distal suture distinct. Antennal peduncle (Fig. 14D, E) slightly shorter than antennular peduncle, extending to mid-length of antennal scale, 4-segmented; second segment narrow, connected to ventral side of third segment; third segment armed dorsally with prominent seta. Antennal sympod (Fig. 14D) with stout denticle at anterolateral corner.

Mandible, mandibular palp, maxillule, and maxilla as illustrated (Fig. 14F–H). Labrum (Fig. 14I) as long as wide, with anterior margin rounded.

First thoracopodal endopod (Fig. 14J) short and robust, armed with strong claw terminally; ischium and merus armed with many slender setae on inner surface. Second thoracopodal endopod (Fig. 15A) relatively robust; merus slightly curved inwardly, almost equal in length to carpopropodus and dactylus combined; carpopropodus slightly swollen in middle part; terminal claw robust. fflird thoracopodal endopod (Fig. 15B, C) slender, showing slight tendency of chela formation involving distomesial seta of distal subsegment of carpopropodus and terminal claw; merus 2.5 times longer than ischium, as long as carpopropodus, dactylus, and terminal claw together; carpopropodus divided into 3 subsegments, proximal subsegment longest and connected obliquely with middle one, distal subsegment shortest, longer than dactylus and terminal claw together. Sixth thoracopodal endopod (Fig. 15D) smaller than third endopod; merus as long as 3-subsegmented carpopropodus; proximal subsegment longer than combined length of succeeding 2 subsegments, connected obliquely with middle one; dactylus and terminal claw both short and small. Eighth thoracopodal endopod (Fig. 15E) much more slender than preceding ones; merus narrow, 2.2 times longer than ischium; carpopropodus and dactylus apparently abnormal. ffloracopodal exopods (Fig. 15A, B, D) with agellum 9-segmented in

rst limb and 10-segmented in second to eighth limbs; basal plate with pointed distolateral corner.

Genital organ of male (Fig. 15F) small, with indistinct inner lobe on distal 1/3; inner lobe not furnished with any setae or spines; apex widely rounded, armed with 5 or 6 long, hooked setae (5 on right organ and 6 on le in allotype); lateral margin with 1 short seta on proximal 1/3; apical part with many scattered spinules. Single sternal process with blunt apex (Fig. 15F) present between genital organs, 2/3 of genital organ in length, with scattered spinules all over.

First abdominal somite 1.2 times as long as second, second to fourth somites subequal, h somite 1.1 times as long as fourth, sixth somite relatively short, 1.5 times as long as h.

All female pleopods reduced to unsegmented single lobes.

fflird male pleopod (Fig. 16A) with both rami equal in length, 16-segmented and without modi ed setae. Exopod of fourth male pleopod (Fig. 16B, D) 17-segmented; inner setae long and plumose; outer setae on distal several segments needlelike apically, shorter and thicker than those of inner ones; penultimate and antepenultimate segments armed with short naked seta in addition to ordinary plumose seta. Endopod of fourth male pleopod (Fig. 16B) 16-segmented, same as exopod in length, without modi ed setae. Fi h male pleopod (Fig. 16E) smaller than preceding one; exopod 13-segmented; endopod damaged distally. Pseudobranchial lobe (Fig. 16A–C, E) widened into at plate.

Uropodal endopod (Fig. 16F, G) tapering distally, slightly extending beyond telson, armed on inner ventral surface in statocyst region with 2, rarely 3, spines, these becoming longer distally. Uropodal exopod (Fig. 16G) overreaching posterior end of telson by 1/3 of its length.

Telson (Fig. 16F, G, J) elongated linguiform with narrowly rounded apex, 2.4 times as long as maximum width near base, 1.3 times as long as last abdominal somite; lateral margin concave in anterior half and slightly convex in posteri- or half, armed on about posterior 2/3 with 41 or 42 rather short spines, these becoming very gradually longer posteriorly; apical pair of spines slightly but distinctly longer than nearest ones; pair of plumose setae emerging from dorsal surface just in front of base of apical spines.

Etymology.ffl e speci c name, sagamiensis , is derived from Sagami Bay, where the present specimens were collected.

Remarks. A mblyops sagamiensis closely resembles A. paci cus . Di erences between these two species are, nonetheless, many: (1) the eyeplate is rather large and extends to the basal margin of the second segment of the antennular peduncle in A. sagamiensis , while it is small and only extends to the basal one-third of the rst segment of the antennular peduncle in A. paci cus ; (2) the eyeplate lacks a distinct papilliform projection in A. sagamiensis whereas the projection is distinct in A. paci cus ; (3) the antennal scale is 3.0 times as long as wide in A. sagamiensis , but 3.4 times as long in A. paci cus ; (4) the genital organ of the male is armed with ve or six hooked setae on the apex in A. sagamiensis rather than three as in A. paci cus ; (5) the uropodal endopod is armed with two or three spines in the statocyst region in A. sagamiensis rather than one spine as in A. paci cus ; (6) the lateral margin of the telson is furnished with 41 or 42 spines in A. sagamiensis as compared to 33 to 37 spines in A. paci cus .

Amblyops sagamiensis is also allied to A. izuensis but can be distinguished from the latter by the following points: (1) the telson lacks a pair of minute apical spines in A. sagamiensis , while such spines are present in A. izuensis ; (2) the several apical pairs of spines on the telson increase very gradually in length posteriorly in A. sagamiensis whereas these spines much more abruptly lengthen posteriorly in A. izuensis ; (3) the genital organ of the male is armed with

ve or six hooked setae on the apex in A. sagamiensis rather than four setae as in A. izuensis ; and (4) the sternal process of male is much bigger in A. sagamiensis than in A. izuensis (cf. Fig. 15F and Fig. 5J, K).

ffle present new species is similar to A. kashimensis in the armature of the telson, but distinguished from the latter species by the shape of the antennal scale.

Specimens reported by Bravo (1996) as Amblyops sp. 1, which was collected from almost the same locations as the type locality of A. sagamiensis , seem to belong to this species. ffley agree with A. sagamiensis in the short and wide antennal scale and the relatively short marginal spines of telson.

Distribution.K nown only from Sagami Bay, Japan ( Bravo 1996; present study).