Amblyops australiensis, 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 : 52-56

Amblyops australiensis sp. nov.

(Figs 3, 4)

Type series.H olotype: near-adult male (10.1 mm), NSMT-Cr 21346, RV “Hakuho Maru”, KH-72-1 Cruise, St. 33, 12°42 .2′S 123°07.6′E to 12°42 .0′S 123°08.5′E, o Sahul Shelf, Timor Sea, 26 June 1972, 535– 547 m, plankton net installed at mouth of 3-m beam trawl, coll . M . Murano . Paratypes: 5 immature males (ca. 9.8, 8.8, ca. 7.2 mm, 2 without abdomen) and 3 immature females (8.5, 7.4, 7.1 mm), NS- MT-Cr 21347, same data as holotype .

Description.C arapace (Fig. 3A) with evenly 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. 3A, B) plate-like without visual elements, separated from each other; each eyeplate wider than long, subisosceles triangular in shape with very short mesial margin, and with marked triangular process on anterior margin; anterolateral corner and dorsolateral surface furnished with spinules.

Male antennular peduncle (Fig. 3A, C) short and robust;

rst segment wider than long, with prolonged anterolateral corner tipped with several setae; second segment very short; third segment as long as wide, with appendix masculina developed.

Antennal scale (Fig. 3A, D) elongated, rather slender, extending beyond anterior margin of third segment of antennular peduncle by half of its length, 4 times as long as maximum width at proximal 1/4, gradually narrowing from widest point to distal end; lateral margin straight, naked, terminating in denticle overreaching rounded apex of blade and armed with subsidiary spinule on inner side; distal suture distinct. Antennal peduncle (Fig. 3A, D) as long as antennular peduncle, not extending to middle of antennal scale, 4-segmented; second segment connected to ventral side of third segment. Antennal sympod (Fig. 3A, D) with strong denticle at anterolateral corner.

Mandible, mandibular palp, outer lobe of maxillule and maxilla as illustrated (Fig. 3F–H). Labrum (Fig. 3I) with rounded anterior margin.

First thoracopodal endopod (Fig. 4A) short and robust, with strong terminal claw; exopod (Fig. 4C) with 9-segmented agellum and slender basal plate with pointed distolateral corner. Second thoracopodal endopod (Fig. 4B) elongated; merus becoming slightly wider distally, slightly curved inwardly; carpopropodus longest, slightly wider in middle part; dactylus nearly 3 times as long as wide, armed with strong claw terminally; exopod with 10-segmented agellum. Almost all endopods of third to eighth thoracopods broken o. In one endopod (original limb site unknown), merus longer than combined length of carpopropodus and dactylus, armed with long seta at distolateral corner; carpopropodus divided into 3 subsegments, proximal subsegment articulating obliquely with middle one, distal subsegment slightly longer than middle one; dactylus short, with distinct terminal claw.

Sixth abdominal somite 1.5 times longer than h.

Male pleopods (Fig. 4D, E) biramous, both rami 12- or 13-segmented except for endopod of rst limb, this being reduced to unsegmented lobe; in holotype (near-adult male) no sign of modi cation of setae observed; pseudobranchial lobe greatly widened, nearly as long as wide. All female pleopods reduced to unsegmented single lobes.

Uropodal endopod (Fig. 4F, G) tapering distally, overreaching posterior margin of telson by about 1/3 of its length, armed with single slender spine on inner margin in statocyst region. Uropodal exopod (Fig. 4F) extending posteriorly beyond posterior margin of telson by about half of its length and beyond apex of uropodal endopod by 1/4 of its length.

Telson (Fig. 4F, H) truncate posteriorly, 1.7 times as long as maximum width near base, 4/5 as long as last abdominal somite; lateral margin straight, armed on posterior 2/5 with 11 or 12 slender spines, these increasing in length posteriorly; posterior margin about 1/5 as wide as basal maximum width, armed with 3 pairs of spines, innermost pair very small, middle pair longest, 1/5 of telson length, outer pair slightly shorter than middle pair; pair of median plumose setae present.

Etymology.ffl e speci c name, australiensis , is derived from Australia, the country o whose northern coast the specimens were collected.

Remarks.ffl e holotype does not appear to be fully mature because the setae on the pleopods are not fully developed, but it is believed to merit formal description due to its well developed appendix masculina.

Amblyops australiensis is allied to A. durbani , in having a marked triangular process on the eyeplate, a slender antennal scale, and a telson armed with 15 spines restricted to less than the posterior half of each lateral margin. It is distinguishable from the latter species by the following points: (1) the carapace leaves the eyeplates nearly completely exposed in A. australiensis , while it covers the posterior half of the eyeplates in A. durbani (O. S. Tattersall 1955: g. 21A); (2) the eyeplates are furnished rather scantily with spinules in A. australiensis whereas they are densely armed with long, slender spinules especially on the anterolateral angles in A. durbani ; (3) the antennal scale is more slender in A. australiensis than in A. durbani (4.0 times as long as wide versus 3.5 times); and (4) the lateral margin of the telson is straight throughout its length and armed with spines on the posterior two- hs in A. australiensis , while it becomes abruptly narrower in the anterior half and is armed with spines on the posterior half in A. durbani .