Amblyops timorensis, 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 : 77-79

Amblyops timorensis sp. nov.

(Figs 20, 21)

Type specimen.H olotype: adult male (7.2 mm), NS- MT-Cr 21366, RV “Hakuho Maru”, KH-72-1 Cruise, St. 27, 09°30 .9′S 127°56.6′E, Timor Sea, 19 June 1972, 465– 490 m, plankton net installed at mouth of 3-m beam trawl, coll . M . Murano.

Description.C arapace (Fig. 20A) with evenly and slightly rounded anterior margin without distinct rostral projection, leaving most of eyeplates exposed; anterolateral corner rounded; posterior margin emarginate, leaving last thoracic somite exposed dorsally.

Eyes (Fig. 20A–C) plate-like without visual elements, small, separated from each other, extending to middle of rst segment of antennular peduncle; each eyeplate quadrangular with rounded corners, with small upturned projection at about center of anterior margin; anterolateral corner slightly swollen, with scattered relatively conspicuous spinules.

Antennular peduncle of male (Fig. 20A, D) robust; rst segment with anterolateral corner projecting laterally and tipped with several setae; second segment very short, with 1 seta on mesial margin and 1 minute seta on lateral margin; third segment as long as wide, more than twice as long as preceding 2 segments combined, with posterolateral corner expanded laterally; appendix masculina large and very hirsute owing to large number of sensory setae emerging from ventral surface.

Antennal scale (Fig. 20A, E) relatively short, slightly overreaching distal end of appendix masculina on antennular peduncle, overreaching distal margin of third segment of antennular peduncle by 1/3 of its length, 2.7 times as long as widest part at about proximal 1/3; apex of blade narrow, more triangular than rounded; distal suture indistinct; lateral margin naked, slightly convex; distolateral denticle not extending to apex of blade, with 1 or 2 subsidiary spinules near base of inner side. Antennal peduncle (Fig. 20E, F) nearly as long as antennular peduncle, 4-segmented; second segment very short, narrow, not showing distinct irregular connection between itself and third segment as in other species of Amblyops . Antennal sympod (Fig. 20E) with small denticle at distolateral angle.

Mandible, mandibular palp, maxillule, and maxilla as illustrated (Fig. 20G–I). Labrum with anterior margin round- ed.

First thoracopodal endopod (Fig. 21A) robust, with long, strong claw terminally. Second thoracopodal endopod (Fig. 21B) relatively robust; merus slightly curved inwardly, longer than combined length of carpopropodus and dactylus; carpopropodus swollen in middle part, 3 times as long as wide; dactylus short, as long as wide, with strong terminal claw. fflird to eighth thoracopodal endopods broken o.

Genital organ of male (Fig. 21D) relatively long, 4.5 times as long as wide, barely extending to distal end of basal plate of eighth thoracopodal exopod, slightly curved anteriorly, armed with 3 hooked setae on apex and 4 setae on middle part of posterior margin.

Fourth abdominal somite shortest, sixth abdominal somite 1.6 times longer than h.

Second male pleopod (Fig. 21E) biramous; both rami equal in length and 11-segmented; exopod with supplemental seta on 10th segment. Fourth male pleopod (Fig. 21F) with 11-segmented endopod and 12-segmented exopod; endopod with slightly modi ed setae on several distal segments; exopod equal to endopod in length, outer setae on distal 4 segments slightly modi ed; these modi ed setae (indicated with wedge in gure) slightly thicker than ordinary ones and needlelike distally; exopodal setae less modi ed than those of endopod; long supplemental seta present on penultimate segment of exopod. Pseudobranchial lobe (Fig. 21E, F) at and expanded.

Uropodal endopod (Fig. 21G, H) tapered, overreaching posterior end of telson by 1/4 of its length, armed with single slender spine on inner ventral margin in statocyst region. Uropodal exopod (Fig. 21G) overreaching apex of telson by about half of its length and apex of uropodal endopod by 1/3 of its length.

Telson (Fig. 21G, I) narrowly linguiform, about as long as last abdominal somite,1.8 times as long as its maximum width near base; lateral margin concave in anterior half and convex in posterior half, armed along posterior 3/5 with about 17 spines gradually increasing in length distally; posterior end narrow, armed with pair of long spines, these being longest among all marginal spines and 1/4 of telson length, about 1.5 times longer than neighboring spines; pair of median plumose setae present.

Etymology.ffl e speci c name, timorensis , is derived from the Timor Sea, where the present specimen was collected.

Remarks. A mblyops timorensis is easily distinguished from the other species of the genus by its (1) small-sized body (7.2 mm in adult male), (2) short and broad antennal scale, (3) short second segment of the antennal peduncle, (4) slender genital organ of the male, and (5) telsonic armature, i.e. 17 spines situated along the lateral margin of the telson and noticeably increasing in size posteriorly.