Meterythrops microphthalmus W. Tattersall, 1951

Fukuoka, Kouki & Murano, Masaaki, 2006, Taxonomy of the genus Meterythrops (Crustacea: Mysida: Mysidae), with a redescription of M. microphthalmus and descriptions of two new species, Journal of Natural History 40 (27 - 28), pp. 1641-1674 : 1645-1651

publication ID	https://doi.org/ 10.1080/00222930600956858
persistent identifier	https://treatment.plazi.org/id/860DB34F-2707-D53A-CD5F-1E37FDFBFA0C
treatment provided by	Carolina
scientific name	Meterythrops microphthalmus W. Tattersall, 1951
status

Treatment

( Figures 2 View Figure 2 , 3 View Figure 3 , 12B, C View Figure 12 )

Meterythrops microphthalma W. Tattersall 1951, p 113 View in CoL –116, Figure 36; Banner 1954, p 580– 581 (in part?); Birstein and Tchindonova 1958, p 305; Ii 1964, p 319; Murano 1971, p 47 (list); 1977, p 171–176; Müller 1993, p 123 (list); Jo et al. 1998, p 40–41, Figure 7 View Figure 7 .

Meterythrops robusta: Taniguchi 1969, p 47 View in CoL –48, Figure 5 View Figure 5 .

Material examined

Type material. USNM 81259 View Materials , type, two males (17.8 and 18.8 mm) and two females (18.8 mm and dissected specimen), Albatross Stn 4800, Chirinkotan Island, the Sea of Okhotsk, 1830 m, 22 June 1906 .

Material reported by Murano (1977). See Table I. On data, see Murano (1977).

Other Japanese material. NSMT-Cr 16689, one juvenile (5.7 mm), Japan Sea off Hokkaido, 3–4 June 1967, R / V Tansei-Maru cruise. NSMT-Cr 16690, two females (11.8 and 14.9 mm) and one juvenile (damaged), Stn H 8-9, east off Hokkaido (44 ° 04.59N, 149 ° 51.89E), 6 December 1967 GoogleMaps , 510– 540 m, horizontal tow with ORI-100 net. NSMT- Cr 16691, one female (18.3 mm) and 14 juveniles (6.8–7.4 mm), Stn H 136-2, Japan Sea (38 ° 19.29N, 135 ° 40.49E), 6 August 1970 GoogleMaps , 0–75 m, oblique tow with ORI-100 net. NSMT- Cr 16692, two males (damaged), off Tokachi (42 ° 16.59N, 143 ° 43.99E), southeastern Hokkaido, northern Japan, from stomach of an eelpout, Zestichthys tanakai Jordan and Hubbs , 1925, collected with a trawl from the sea floor at a depth of 412 m, 13 June 1989, coll. Yamamura. GoogleMaps NSMT-Cr 16693, one female (14.7 mm), off Kushiro (42 ° 40.09N, 144 ° 51.39E), southeastern Hokkaido, northern Japan, from stomach of an eelpout, Zestichthys tanakai , collected with a trawl from the sea floor at a depth of 424 m, 15 June 1989, coll. Yamamura. GoogleMaps NSMT-Cr 16694, one immature female (11.1 mm), off Kushiro (42 ° 40.89N, 144 ° 52.29E), southeastern Hokkaido, northern Japan, from stomach of a scorpion fish, Sebastolobus macrochir (Günther, 1880) , collected with a trawl from the sea floor at a depth of 317 m, 15 June 1989, coll. Yamamura. GoogleMaps

Alaskan material. NSMT-Cr 16687, one male (15.9 mm), dissected, S139A, Shelikof Strait, Alaska, sledge, date unknown. NSMT-Cr 16688, two males (13.3 and 15.0 mm) and two females (11.8 and 14.8 mm), same data as NSMT-Cr 16687.

Description

Body robust, constricted between thorax and abdomen. Integument smooth. First to third abdominal somites with blunt small process on median line of ventral side; first somite 1.4 times as long as second, second to fifth somites subequal, and sixth somite twice as long as preceding one.

Carapace produced anteriorly into triangular rostral plate with blunt apex extending slightly beyond base of antennular peduncles; lateral margins of rostrum slightly convex; anterolateral corner pointed; posterior margin emarginate, leaving last thoracic somite exposed dorsally ( Figure 2A, B View Figure 2 ).

Eyes small, subcylindrical, equal to or narrower than width of proximal segment of antennular peduncle, 1.3–1.5 times as long as broad in dorsal view; cornea occupying about two-fifths of eye, only slightly wider than stalk; eyestalk with papilliform process on dorsal surface ( Figure 2A, B View Figure 2 ).

Antennular peduncle of male more robust than that of female, third segment 1.3 times as long as first, 1.3 times as long as broad, with developed appendix masculina; third segment of female 1.4 times as long as broad ( Figure 2A, B View Figure 2 ).

Antennal scale extending beyond antennular peduncle for one-third of its length, about four times as long as broad; lateral margin naked, terminating in spiniform process; apical lobe occupying three-sevenths of scale in length, twice as long as broad at base, with suture near apex ( Figure 2 View Figure 2 A–C). Antennal peduncle robust, extending to distal two-fifths of scale ( Figure 2C View Figure 2 ). Antennal sympod with spiniform process at lateral distal corner ( Figure 2C View Figure 2 ).

Labrum without frontal process.

Mandibular palp: second segment 3.5 times as long as broad, armed with numerous setae on mesial and lateral margins; third segment two-fifths of second in length ( Figure 2D View Figure 2 ).

Maxillule: lateral lobe armed with about 12 spines on distal margin and three barbed setae on ventral surface, lateral margin with fine setae on distal half and small lobe in middle ( Figure 2E View Figure 2 ).

Maxilla: second segment of endopod 1.7 times as long as broad, without spines on margins ( Figure 2F View Figure 2 ).

First thoracopodal endopod short, robust. Second thoracopodal endopod rather slender; carpopropodus slightly shorter than merus. Third to eighth thoracopodal endopods long, slender; carpopropodus divided into three subsegments, proximal articulation running obliquely and distal articulation transversely ( Figure 2G View Figure 2 ).

Penis armed with 10 short setae on posterolateral margin; apex bilobed, anterior lobe overreaching posterior one, triangular in lateral view, posterior lobe broadly rounded, armed with about 10 long, mesially curved setae ( Figure 3A View Figure 3 ).

Female with tuft of setae on coxa of sixth thoracopod and with developed oostegite on seventh and eighth thoracopods; oostegite on seventh thoracopod with baling lobe.

All pleopods of male well developed, biramous ( Figure 3 View Figure 3 B–F). First pleopod with endopod reduced to unsegmented lobe extending to distal margin of third segment of exopod; exopod 14-segmented ( Figure 3B View Figure 3 ). Second to fourth pleopods with 12-segmented endopod and 12-segmented exopod, both rami almost same length, without modified setae ( Figure 3 View Figure 3 C–E). Fifth pleopodal endopod 10-segmented, longer than exopod, armed on ultimate segment with pair of modified setae, which are slightly longer and thicker than normal setae, and furnished with rather long, fine setae on proximal half and short setae on distal half except for distal one-fifteenth naked ( Figure 3F, G View Figure 3 ). Fifth pleopodal exopod 10- segmented, terminating in normal plumose seta and modified seta, latter seta 1.6 times as long as former one, furnished with fine setae on proximal two-thirds and spinulated on distal one-third except for distal one-eleventh naked ( Figure 3F View Figure 3 ).

All pleopods of female reduced to unsegmented single lobe, gradually increasing in length towards posterior pair.

Endopod of uropod tapered, overreaching telson for distal one-fourth of its length, armed with 22–28 small, subequal spines on mesial margin from statocyst region to distal one-fourth to one-third ( Figure 3 View Figure 3 H–J). Exopod of uropod slightly curved laterally, 1.4 times longer than endopod ( Figure 3H, J View Figure 3 ).

Telson elongated triangular with narrowly truncate apex, 1.2 times as long as last abdominal somite, 1.7–2 times as long as maximum width; lateral margin without spines, almost straight; posterior margin narrow, armed with two pairs of slender spines, mesial pair of which is 1.4 times longer than lateral one, and with median pair of plumose setae ( Figure 3J View Figure 3 ).

Distribution

This species has been recorded from the cold-water region of the western North Pacific: the Sea of Okhotsk ( Tattersall 1951; Birstein and Tchindonova 1958), the Japan Sea ( Tattersall 1951; Murano 1977; Jo et al. 1998), the Pacific Ocean off the Kurile Islands ( Birstein and Tchindonova 1958; Murano 1977) and the Pacific Ocean off northeastern and central Japan ( Taniguchi 1969; Murano 1977). The present collection from Alaskan waters is the first record from the eastern North Pacific.

This species is distributed in the mesopelagic zone ( Tattersall 1951; Murano 1977; Ikeda 1991). Murano (1977) reported this species from depths of 350 to 2000 m in the daytime and 0 to 1650 m in the nighttime in the northern part of the Japan Sea. Ikeda (1991) also reported the major population of this species inhabited consistently below 250 m in the Toyama Bay, the Japan Sea.

Remarks

Meterythrops microphthalmus was established by W. Tattersall (1951) on the basis of specimens collected from the Sea of Okhotsk and the Japan Sea. He did not provide a full description, noting only differences from the most closely related species, M. robustus , in the eyes, antennal scale, and uropodal endopod. We report the first thorough description of this species.

W. Tattersall (1951) noted that this species lacks spines on the mesial margin of the uropodal endopod. However, they are armed with 22–28 spines, as already pointed out by Taniguchi (1969), Murano (1977), and Jo et al. (1998). We confirmed this feature in the type specimens. In addition, we report that males have modified setae on both the endopod and the exopod of the fifth pleopod, although this could not be confirmed in the type specimens because they were damaged.