Amblyops manazuruensis, 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 : 60-64

Amblyops manazuruensis sp. nov.

(Fig. 8)

Amblyops sp. 2: Bravo 1996: 38–41, gs 29–31.

Type series.H olotype: adult female (damaged, ca. 11 mm), NSMT-Cr 21351, “Tansei Maru”, KT-69-6 Cruise, St. 341, 35°04 .4′N 139°09 .9′E , Sagami Bay o Cape Manazuru, central Japan, 9 May 1969, 00:10–01:05, 360–460 m, bottom-net, coll . M . Murano . Paratypes: 2 adult females (one damaged, ca. 13 mm, another broken into 3 pieces), NSMT-Cr 21352, same data as holotype .

Description.C arapace (Fig. 8A) with evenly rounded anterior margin without distinct rostral projection, leaving most of eyes exposed; anterolateral corner of carapace rounded.

Eyes (Fig. 8A, B) plate-like without visual elements, separated from each other, extending beyond middle of rst segment of antennular peduncle; each plate rhomboidal with rounded corners, wider than long; anterior margin almost straight, without distinct papilliform projection in dorsal view, but upturned small knob detectable in lateral view; margins and dorsal surface inconspicuously spinulose.

Antennular peduncle (Fig. 8A) robust; rst segment with anterolateral corner prolonged anteriorly and tipped with several setae; second segment very short; third segment slightly longer than wide, armed with 6 or 7 setae along mesial margin and several long setae on distomesial margin.

Antennal scale (Fig. 8A, C) rather slender, 3.8 times as long as maximum width at about proximal 1/4, extending beyond distal margin of third segment of antennular peduncle by half of its length, becoming gradually narrower from widest part to apical end; lateral margin naked, straight, terminating in stout denticle, latter extending as far as narrowly rounded apex of blade and possessing subsidiary spinule near basal end of inner side; distal suture distinct. Antennal peduncle (Fig. 8A, C, D) slightly shorter than antennular peduncle, about 2/5 as long as scale, 4-segmented; second segment connected to ventral side of third segment; third segment armed with prominent seta on dorsal surface. Antennal sympod (Fig. 8A, C) with stout denticle at distolateral corner.

ffloracic appendages broken o.

First abdominal somite 1.3 times longer than second, second to h somites subequal, sixth somite 1.7 times longer than h.

All female pleopods reduced to unsegmented single lobes.

Uropodal endopod (Fig. 8E, F) tapering distally, overreaching posterior end of telson by 1/4 of its length, armed with 2 spines on inner ventral surface in statocyst region. Uropodal exopod (Fig. 8E) elongated, overreaching apex of endopod by 1/3 of its length.

Telson (Fig. 8G, H) linguiform, 1.1 times longer than last abdominal somite, 1.8 times as long as maximum width near base, abruptly narrowing close to base, thence gradually narrowing to rounded apex; lateral margin armed on posterior 4/5 with 24 to 26 spines, these gradually becoming longer posteriorly except apical 4 spines increasing markedly in length, apical pair of long spines 1/5 as long as telson; single or 2 minute spines present between apical long spines, in case of 2 spines these closely set and united basally (Fig. 8I); pair of feeble median plumose setae emerging from dorsal surface close to apex.

Etymology.ffl e speci c name, manazuruensis , is derived from Cape Manazuru, the locality o which the specimens were collected.

Remarks.M ales of A. manazuruensis were not available for study, and thus the following comparison with the most closely allied species, A. izuensis , is based on the male of the latter species. In mysids in general, noticeable morphological di erences between males and females do not exist except for some secondary sexual characteristics that appear with growth involving the antennules, genital organs, and pleopods. Female of this new species and male of A. izuensis are similar in having no distinct papilliform projection on the anterior margin of the eyeplate, a linguiform telson with one or two spinules at the apex, and several apical pairs of spines of the telson markedly increasing in length posteriorly, but the former is distinguished from the latter in the following respects: (1) the antennal scale is proportionally narrower and more strongly tapered in the former (3.8 times as long as wide versus 3.3 times as long) (see Figs 8C and 5C); (2) the antennal peduncle is proportionally shorter (about two- hs of the antennal scale length versus more than half as long); and (3) the telson is armed with 24–26 spines on the posterior four- hs in the former as compared to 28–30 spines on the posterior two-thirds in the latter.

Amblyops manazuruensis is also allied to A. kempi but differs from the latter species as follows (cf. Holt and Tattersall 1905, and Tattersall and Tattersall 1955): (1) the eyeplate lacks a papilliform projection on the anterior margin in this new species, while it has a projection near the outer corner of the anterior margin in the latter species; (2) the distolateral denticle of the antennal scale extends only as far as the apex of the blade in A. manazuruensis , but beyond that point in A. kempi ; and (3) the telson gradually narrows posteriorly in this new species, while in A. kempi it is abruptly constricted near the base, then tapers very slightly to the apex.

Amblyops manazuruensis seems to be identical with Amblyops sp. 2 reported from the same locality by Bravo (1996), agreeing particularly closely in features of the antennal scale and telson. Nevertheless, there is a di erence in the eyeplate: a distinct papilliform projection was present in Bravo’s (1996) specimens, while in the present specimens it was not apparent in dorsal view, only in lateral view. Bravo (1996) reported variation in the number of minute apical spines (1 or 2) and in the length of the longer apical spines of the telson in his specimens of Amblyops sp. 2. In the present specimens, similar variation is seen in the number of minute apical spines, although the length of the longer spines is constant among specimens.

Distribution.On ly known from Sagami Bay, central Japan ( Bravo 1996; present study).