Amblyops paci cus

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 : 65-70

Amblyops paci cus sp. nov.

(Figs 11–13)

Amblyops abbreviatus: Banner 1948: 382–383 ; W. M. Tattersall 1951: 128–130, g. 44 (in part, Paci c specimens); Banner 1954: 581; BirsteinandTchindonova 1958: 319;

Ii 1964: 272–274; Kathman et al. 1986: 96–97, gs a–m; Price 2004: 59; Fukuoka 2009: 419–420.

Type series. H olotype: adult male (12.4 mm), NSMT- Cr 21355, RV “Hakuho Maru”, KH-67-5 Cruise, St . H8- 9, 44°05.1′N 149°51.5′Eto 44°03 .8′N 149°52.0′E (depth ofseaoor, ca. 7000 m), PacicOceanosouthernKu- 44°01.8′N 149°51.0′Eto 44°00 .0′N 149°52 .7′E (depth rile Islands , 6 December 1967, 03:25–05:08, 510–540 m, of sea oor, ca. 7230 m), Paci c Ocean o southern Kuoblique +horizontal haul with ORI net with opening-closing rile Islands, 6 December 1967, 05:25–07:37, 830– 1000 m, device, coll . M . Murano . Paratype: 1 female (damaged, ca. oblique+horizontal haul with ORI net with opening-closing 12.3 mm), NSMT-Cr 21356, same data as holotype . Para- device, coll . M . Murano . Four immature males (10.8, ca. 9.8, type: 1 immature female with partially developed marsupi- 9.2 mm, damaged) and 2 immature females with partially um (11.4 mm), NSMT-Cr 21357, RV “HakuhoMaru”, KH-developedmarsupium (11.5, 10.1 mm), NSMT-Cr 21360, 67-5 Cruise, St . H9-10, 43°52.8′N 149°58.2′Eto 43°55.8′NRV “TanseiMaru”, KT-69-19 Cruise, St. 192, 39°40 .8′N 149°59 .8′E (depthofseaoor, ca. 9060 m), PacicOcean 142°39.9′Eto 39°39 .0′N 142°39 .7′E (depthofseaoor, ca. o southern Kurile Islands , 7 December 1967, 02:48–04:05, 900 m), east of Cape Hei, Iwate Prefecture, northern Japan, 1200–0 m oblique haul with ORI net, coll . M . Murano. 27 September 1969, 18:58–19:49, 900–0 m oblique haul with Other material examined. T wo immature females ORI net.

(9.8, 7.5 mm), NSMT-Cr 21358, RV “HakuhoMaru”, KH- Description.Body (Fig. 11) moderatelyrobust. Cara- 67-5 Cruise, St. H8-6, 44°10.8′N 149°49.6′Eto 44°09.2′Npace (Fig. 12A, B) withbroadlyroundedanteriormargin 149°49 .7′E (depth of sea oor, ca. 6430 m), Paci c Ocean o without de nite rostral projection, leaving most of eyes southernKurileIslands, 5–6 December 1967, 23:55–01:00, exposed; anterolateralcornerrounded; posteriormargin 250–540 m, oblique+horizontal haul with ORI net with emarginate, leaving posterior half of last thoracic somite exopening-closing device, coll . M . Murano. One adult female posed dorsally.

(11.7 mm) and 1 immature female (11.5 mm), NSMT-Cr Eyes (Fig. 12A–C) plate-like without visual elements, 21359, RV “Hakuho Maru”, KH-67-5 Cruise, St. H8-10, separated from each other, extending to basal 1/3 of rst segment of antennular peduncle; each eyeplate quadrangular with rounded corners, rather small, wider than long, with distinct papilliform projection on dorsal surface near center of anterior margin; distolateral corner rounded, slightly swollen anteriorly especially in female, scattered with minute spinules; lateral margin twice longer than inner.

Antennular peduncle of male (Fig. 12A) robust; rst segment wider than long, distolateral corner prolonged and tipped with several setae; second segment very short; third segment slightly longer than wide; appendix masculina well developed and hirsute. Antennular peduncle of female (Fig. 12B, D) more slender than in male; second segment very short, with lateral margin produced into small triangular process tipped with 2 short setae; third segment 1.3 times as long as wide, armed with 6 setae on distal 2/3 of mesial margin and about 6 setae on distomesial margin.

Male antennal scale (Fig. 12A, E, F) extending to apex of appendix masculina and beyond distal margin of third segment of antennular peduncle by about 1/3 of its length, 1.3 times as long as antennal peduncle, 3.4 times as long as greatest width at about proximal 1/3; distolateral denticle barely extending to apex of blade, subtriangular with subsidiary spinule near basal end of inner side. Female antennal scale (Fig. 12B, G) proportionally smaller than that of male, 1.4 times as long as antennal peduncle, 3.5 times as long as wide, extending beyond distal margin of antennular peduncle by 2/5 of its length. Antennal peduncle of both sexes (Fig. 12A, B, E, G) as long as antennular peduncle, 4-segmented; second segment connected to ventral side of third segment. Antennal sympod (Fig. 12E, G) with stout denticle at anterolateral corner.

Mandible, mandibular palp, outer lobe of maxillule, and maxilla as illustrated (Fig. 12H–J). Labrum with anterior margin rounded.

First thoracopodal endopod (Fig. 13A) short and robust; dactylus half as long as carpopropodus, terminating in strong claw longer than dactylus. Second thoracopodal endopod (Fig. 13B) elongated and slender, with strong claw terminally; merus slightly curved inwardly, almost as long as carpopropodus and dactylus combined; carpopropodus slightly swollen in middle part; exopod with 10-segmented

agellum, basal plate with pointed distolateral corner. Endopods of third to eighth thoracopods of type specimens broken o, except for third limb in one paratype (NSMT- Cr 21357): endopod of third limb (Fig. 13C) slender; merus longer than carpopropodus; carpopropodus 3-subsegment- ed, articulation between rst 2 subsegments very oblique, distal subsegment slightly longer than middle; dactylus broken.

Genital organ (Fig. 13E) 2–2.5 times as long as broad, armed with 3 long, hooked, naked setae on apex. Small sternal process (Fig. 13E) present between genital organs.

First, fourth, and h abdominal somites 1.2 times longer than second, third segment equal to second in length, sixth somite almost twice as long as h.

Fourth pleopodal endopod of male (except for setae) (Fig. 13F, G) slightly extending posteriorly beyond posterior margin of sixth abdominal somite, 13-segmented; plumose setae of distal 5 segments slightly stouter than those of preceding segments and naked distally; pseudobranchial lobe widened; exopod broken o. Fi h male pleopod (Fig. 13H) smaller than fourth; exopod 11-segmented, without modi ed setae; endopod with pseudobranchial lobe widened.

All pleopods of female reduced to unsegmented single lobes.

Uropodal endopod (Fig. 13I) tapering distally, overreaching posterior end of telson by 2/9 of its length, armed with single slender, acute spine on inner ventral surface in statocyst region. Uropodal exopod damaged in holotype, but in one of paratypes (NSMT-Cr 21357) extending beyond apex of uropodal endopod by 1/3 of its length.

Telson (Fig. 13I, J) elongated linguiform, slightly more than twice as long as maximum width near base, 1.15 times as long as last abdominal somite; lateral margin concave in anterior half and convex in posterior half, armed with 37 spines on less than posterior 3/4 of le side and 33 spines on more than 2/3 of right side, these spines slightly shorter in anterior part and slightly longer in posterior part, apical pair of spines distinctly longer than others; pair of plumose setae emerging from dorsal surface just in front of base of apical pair of spines.

Etymology.ffl e speci c name, paci cus, is derived from the Paci c Ocean, from which the specimens were collected.

Remarks. A mblyops paci cus most closely resembles A. abbreviatus from the North Atlantic, but is distinguished from the latter species by the following morphological features: (1) the papilliform projection on the anterior median border of the eyeplate is much longer in A. paci cus (1.5 to 2.0 times as long as wide) than those illustrated by G. O. Sars (1872: pl. 6, gs 3, 22) and Tattersall and Tattersall (1951: g. 56B, C) for A. abbreviatus (less than as long as wide); (2) in A. paci cus there is no marked sexual dimorphism in the papilliform projection and the projection is distinct even in the male, while in A. abbreviatus the projection on the eyeplate exhibits a sexual dimorphism, i.e. that of the male is much less marked and represented by a curved row of very ne spinules ( Tattersall and Tattersall 1951); (3) the antennal scale is 1.3 times as long as the antennal peduncle in the male and 1.4 times as long in the female in A. paci cus as compared to about twice as long in A. abbreviatus (G. O. Sars 1872: pl. 6, g. 5; Tattersall and Tattersall 1951: g. 56A); (4) the antennal scale overreaches the distal margin of the antennular peduncle by only about onethird in the male and two- hs in the female in A. paci - cus as against half its length in A. abbreviatus ; (5) ffle lateral margin of the telson is armed with more spines in A. paci - cus (33 to 37) than in A. abbreviatus (26 or 27); (6) the spine in the statocyst region of the uropodal endopod is acute in A. paci cus but blunt in A. abbreviatus ( Tattersall and Tattersall 1951) ; and (7) the genital organ of the male is armed with only 3 setae on the apex in A. paci cus versus 7 setae in A. abbreviatus (G. O. Sars 1872: pl. 6, gs 25, 26).

ffle above results made necessary a reexamination of supposed A. abbreviatus reported previously from the Paci c. fflere are collection records by three researchers, Banner (1948), W. M. Tattersall (1951), and Fukuoka (2009). Among them, Fukuoka's specimens (NSMT-Cr 19670 and 19671), which were collected from the same area as the present A. paci cus , were examined on loan from the National Museum of Nature and Science, Tokyo, and con-

rmed to be identical with the present new species, being in agreement on such main characters as the eyeplate, antenna, and telson. As for the material of Banner (1948) and W. M. Tattersall (1951), both researchers noted that the eyeplate was provided with a larger papilliform projection than that of the typical form of A. abbreviatus , and W. M. Tattersall (1951) reported that the telson of his specimens was armed with a greater number of lateral spines (28 to 32) than occur in Atlantic A. abbreviatus (about 25). fflese data indicate that their specimens from the Paci c belong to A. paci cus , not A. abbreviatus . Furthermore, one of the collection sites for W. M. Tattersall’s (1951) material was the Kurile Islands not far from the type locality of A. paci cus . At present, there is no con rmation of the occurrence of A. abbreviatus in the Paci c.

ffle present specimens were taken from the meso- to bathypelagic zone shallower than 1200 m deep where the bottom depths are 6000 to 9000 m. fflis species thus seems to have a swimming habit in the middle layer as well as an epibenthic life mode. To the contrary, A. abbreviatus is only known as an epibenthic species living on the sea oor at depths of 360 to 630 m ( Tattersall and Tattersall 1951).

Distribution.K nown from the Aleutian Islands (W. M. Tattersall 1951), the Kurile Islands (W. M. Tattersall 1951; Birstein and Tchindonova 1958; present study), the Sea of Okhotsk ( Birstein and Tchindonova 1958), o Japan ( Fukuoka 2009; present study), o southern Alaska (W. M. Tattersall 1951; Banner 1954), and o British Columbia ( Banner 1948, 1954).