Amblyops okinawensis, 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 : 64

Amblyops okinawensis sp. nov.

(Figs 9, 10)

Type series. H olotype: adult female (11.2 mm), NS- MT-Cr 21353, RV “Hakuho Maru”, KH-73-2 Cruise, St . 4, 27°06 .8′N 128°41.9′E to 27°06 .7′N 128°41 .8′E , northeast of Okinawa Island , southwestern Japan, 24 February 1973, 04:28–05:30, 870– 945 m, plankton net installed at mouth of 3-m beam trawl, coll . M . Murano . Paratype: 1 juvenile (6.1 mm), NSMT-Cr 21354, same data as holotype .

Description.C arapace (Fig. 9A) with broadly rounded anterior margin without distinct rostral projection, covering basal 1/3 of eyeplates; anterolateral corner of carapace rounded; posterior margin emarginate, leaving posterior half of last thoracic somite exposed dorsally.

Eyes (Fig. 9A–C) plate-like without visual elements, separated from each other; each eyeplate rather small, wider than long, extending to distal margin of rst segment of antennular peduncle; distolateral corner slightly swollen; outer margin longer than inner; upturned small papilliform projection present on dorsal surface near center of anterior margin; both anterior corners, especially outer one, fringed with many conspicuous spinules.

Female antennular peduncle (Fig. 9A, D) short and robust; rst segment with distolateral corner prolonged and tipped with several setae; second segment very short, armed with 1 seta at middle of mesial margin; third segment as long as wide, armed with about 8 long setae along distal 2/3 of mesial margin, 5 on ventral surface of distomesial part, and 2 short ones at middle of dorsolateral margin.

Female antennal scale (Fig. 9A, E) relatively wide, 3 times as long as greatest width at about proximal 1/3, extending beyond distal margin of third segment of antennular peduncle by nearly half of its length; outer margin naked, slightly convex in proximal half and straight in distal half; distolateral denticle not extending to apex of blade, armed with spinule near base of inner side; distal suture distinct. Antennal peduncle (Fig. 9A, F) slightly longer than antennular peduncle, 4-segmented; second segment connected to ventral side of third segment. Antennal sympod (Fig. 9A) with stout denticle at distolateral corner.

Mandibular palp and maxilla as illustrated (Fig. 9G, H).

First thoracopodal endopod (Fig. 10A) short and robust, with stout claw terminally; dactylus shorter than terminal claw, armed with many barbed setae. Second thoracopodal endopod (Fig. 10B) elongated; merus slightly curved inwardly, almost same in length as combined carpopropodus and dactylus; carpopropodus slightly broader in middle part than in proximal and distal parts; terminal claw stout, as long as dactylus. fflird thoracopodal endopod (Fig. 10C) relatively robust; ischium with lateral margin swollen and armed with 1 seta; merus longer than combined carpopropodus and dactylus; carpopropodus divided into 3 subsegments, proximal subsegment connected very obliquely with middle one, middle subsegment as long as proximal one, distal subsegment much shorter than middle one; dactylus small, with strong claw terminally. Fourth thoracopodal endopod (Fig. 10D) longer and more slender than third endopod; ischium with lateral margin swollen and armed with 4 setae; merus almost equal in length to carpopropodus; carpopropodus 3-subsegmented, proximal subsegment separated from middle one by oblique articulation, middle subsegment shorter than proximal subsegment and longer than distal one; dactylus small, with strong claw terminally. Eighth thoracopodal endopod (Fig. 10E) smaller and more slender than those of third and fourth thoracopods; merus slightly curved inwardly, as long as 3-subsegmented carpopropodus; proximal subsegment of carpopropodus longer than combined length of following 2 subsegments. ffloracopodal exopods (Fig. 10B–D, F) with 10-segmented agellum; basal plate with pointed distolateral corner.

fflird and fourth abdominal somites shorter than others;

h somite 1.1 times longer than fourth; sixth somite 1.9 times longer than h.

All female pleopods reduced to unsegmented single lobes.

Uropodal endopod (Fig. 9I, J) tapering distally, slightly overreaching tips of apical spines of telson, armed with single slender spine on inner ventral surface in statocyst region. Uropodal exopod (Fig. 9I) elongated, 1.5 times longer than endopod, extending beyond apex of telson by 2/5 of its length.

Telson (Fig. 9I, K) elongated triangular with narrowly rounded apex, 1.2 times as long as last abdominal somite, 2.25 times as long as maximum width close to base, narrowing abruptly from widest point to anterior 1/3, thence narrowing gradually to apex; ratio of widths at mid-length and base (widest part) 0.44; lateral margin concave in anterior half and straight in posterior half, armed with about 32 spines on posterior 2/3, these spines almost same in length except for several shorter anterior spines and apical pair of longer spines, latter 1.1 times longer than adjacent ones; pair of feeble plumose setae emerging from dorsal surface just in front of apical spines.

Etymology.ffl e speci c name, okinawensis , is derived from Okinawa, the island o which the specimens were collected.

Remarks.On ly a single adult female specimen is available for this new species, in addition to one juvenile. Amblyops okinawensis is easily distinguished from all known species of the genus by the characteristics of the telson: (1) it is very narrow, the width at the mid-length being only 0.44 of the maximum width (more than 0.5 in congeners); and (2) the marginal spines of the telson are subequal in length except for several pairs of shorter anterior spines and the apical pair of longer spines.

Abnormal setae which must have been a ected by a parasite were found on the mouth parts and thoracic limbs (Figs 9G, 10D, E).