Amblyops izuensis, 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 : 56-59

Amblyops izuensis sp. nov.

(Figs 5, 6)

? Amblyops spiniferus: Bravo 1996: 36–38 , gs 26, 27.

Type series.H olotype: adult male (ca. 13.5 mm), NS- MT-Cr 21348, “Tansei Maru”, KT-78-3 Cruise, St. B57, Sagami Bay o Inatori, Izu Peninsula, central Japan, 9 March 1978, 1685– 1708 m, 2-m beam trawl, coll . S . Ohta . Paratypes: 1 adult female (without cephalon), 1 immature male (12.5 mm), 1 female (damaged), NSMT-Cr 21349, same data as holotype .

Description.A nterior margin of carapace unknown due to damage. Carapace with anterolateral corner rounded; posterior margin emarginate, leaving last thoracic somite exposed dorsally.

Eyes plate-like without visual elements, separated from each other; each eyeplate (Fig. 5A) wider than long, with trace of papilliform projection at about center of anterior margin; anterolateral corner rounded, scattered with spinules.

Male antennular peduncle (Fig. 5B) short and robust; rst segment wider than long, distolateral corner prolonged and tipped with several setae; second segment very short; third segment almost as long as wide; appendix masculina well developed and very hirsute.

Antennal scale (Fig. 5C) extending beyond distal margin of antennular peduncle by half of its length, 3.3 times as long as greatest width at about proximal 1/3; lateral margin slightly convex, naked, terminating in denticle extending slightly beyond apex of blade and armed with spinule near basal end of inner side; distal suture distinct. Antennal peduncle (Fig. 5C, D) as long as antennular peduncle, 4-segmented; second segment connected to ventral side of third segment. Antennal sympod (Fig. 5C) with stout denticle at anterolateral corner.

Second segment of mandibular palp (Fig. 5E) armed densely with slender setae, especially in distal 1/3 of lateral margin, mesial margin armed rather sparsely with setae; third segment armed with short and regularly arranged setae all along lateral margin. Maxillule and maxilla as illustrated (Fig. 5F, G). Labrum with rounded anterior margin.

First thoracopodal endopod (Fig. 5H) short and robust, with stout terminal claw. Second thoracopodal endopod (Fig. 5I) relatively robust; merus slightly longer than combined length of carpopropodus and dactylus; carpopropodus slightly wider in middle part; dactylus longer than wide, with strong terminal claw. fflird to eighth thoracopodal endopods broken o in holotype. ffloracopodal exopods (Fig. 5H) with 9- or 10-segmented agellum. Basal plate of rst thoracopodal exopod (Fig. 5H) with rounded distolateral corner.

Genital organ of male (Fig. 5J, K) elongated conical with rounded apex armed with 4 hooked naked setae; lateral margin with small lobe armed with 3 plumose setae. Conical sternal process (Fig. 5J, K) present between male genital organs.

First abdominal somite 1.1 times as long as second, second to fourth somites subequal, h somite 1.1 times longer than fourth, sixth somite 1.6 times longer than h.

First male pleopod (Fig. 6A) with 17-segmented exopod and unsegmented endopod; endopod extending to distal margin of sixth exopodal segment. Second and third male pleopods (Fig. 6B, C) with 18-segmented exopod and 17-segmented endopod, both equal in length. fflird thoracopodal exopod armed with naked accessory seta in addition to ordinary plumose one at distomesial corners of 13th, 14th, 16th, and 17th segments. Fourth pleopodal exopod of male (Fig. 6D, F) 18-segmented, armed with modi ed seta at distolateral corner of 13th to 18th (ultimate) segments and distomesial corner of 17th and 18th, and with naked accessory setae at distomesial corner of 13th, 15th, 16th, and 17th segments, those on 16th and 17th segments prominent. Fourth pleopodal endopod of male (Fig. 6D, E) 17-segment- ed, same as exopod in length, armed with modi ed seta at distolateral corner of 13th to 17th (ultimate) segments and distomesial corner of 15th to 17th segments. fflese modi-

ed setae on both rami slightly stouter than ordinary plumose setae and needlelike apically. Fi h male pleopod (Fig. 6G) smaller than preceding limbs, endopod 15-segmented, exopod damaged. Pseudobranchial lobe (Fig. 6A–D, G) widened. All female pleopods reduced to unsegmented single lobes.

Uropodal endopod (Fig. 6H, I) tapering distally, reaching tips of long apical spines of telson, armed with 3 slender spines on inner ventral surface of statocyst region. Uropodal exopod (Fig. 6H) overreaching apex of telson by 2/5 and uropodal endopod by 1/3 of its length.

Telson (Fig. 6H, J) elongated linguiform, slightly less than twice as long as maximum width near base, almost as long as last abdominal somite, narrowing gradually towards narrow apex; lateral margin slightly concave in anterior half and slightly convex in posterior half, armed with 28–30 spines on about posterior 2/3, these spines, especially in posterior several pairs, increasing in length posteriorly; apex armed with pair of minute median spines and pair of long spines, latter 1/5 as long as telson; pair of plumose setae emerging from dorsal surface just in front of bases of apical minute spines.

Etymology.ffl e speci c name, izuensis , is derived from Izu Peninsula, near which the specimens were collected.

Remarks. A mblyops izuensis most closely resembles A. kempi and A. spiniferus in having one or two small median spines on the rounded apex of the telson. Di erences from A. kempi are recognized in the shape of the antennal scale and the shape and armature of the telson. In A. izuensis the antennal scale is more gradually tapered than in A. kempi , and the telson gradually narrows posteriorly and is armed with 28–30 spines on the posterior two-thirds of the lateral margin, while in A. kempi the telson abruptly narrows close to the base and then becomes almost parallel-sided and armed with 27–28 spines on the posterior four- hs (cf. Holt and Tattersall 1905 and Tattersall and Tattersall 1955). Amblyops izuensis is distinguished from A. spiniferus by the structure and armature of the telson (cf. Nouvel and Lagardère 1976): (1) the telson is devoid of a constriction near the base in the new species whereas a distinct constriction is present near the base in A. spiniferus ; (2) the lateral margin is furnished with spines on the posterior two-thirds in A. izuensis rather than the posterior half as in A. spiniferus ; and (3) the longest apical spines are proportionally longer in A. spiniferus (about one- h as long as the telson versus oneninth as long).

ffle specimens identi ed tentatively as A. spiniferus by Bravo (1996) are judged to belong to A. izuensis because similarities in the shape of the antennal scale and the aspect of the marginal spines of the telson are consistent with this species.

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