Brachyscelus rapax ( Claus, 1871 )

Zeidler, Wolfgang, 2021, A review of the hyperiidean amphipod family Brachyscelidae Stephensen, 1923 (Crustacea: Amphipoda: Hyperiidea), Zootaxa 5026 (3), pp. 405-439 : 426-430

Brachyscelus rapax ( Claus, 1871)

( Figs 11–12 )

Schnehagenia rapax Claus, 1871: 157 .

Thamyris rapax — Claus 1879: 182 (36).— Claus 1880: 588.— Bovallius 1887a: 30.— Claus 1887: 59, pl. 17, figs 1–8.

Brachyscelus rapax — Barnard 1932: 292 (one of three specimens only).— Barnard 1940: 520 (list).— Siegfried 1963: 6 (list), 12 (table).— Dick 1970: 69.— Vinogradov et al. 1982 /1996: 396/489 (key), 400/493–495, fig. 215 (part; B. rapacoides regarded a synonym; fig. is of B. rapacoides ).— Barkhatov & Vinogradov 1988: 168 (table).—Vinogradov 1990: 77, 95 (table).— Vinogradov 1991: 261 (table), 262.— Zeidler 1992: 115 (key).— Vinogradov 1993: 45 (table).— Shih & Chen 1995: 178 (key), 181–182, fig. 118.— Lin et al. 1996: 231 (table).— Vinogradov & Semenova 1996: 618.— Barkhatov et al. 1999: 808 (table).— Vinogradov 1999: 1145 (table), 1193 (key), 1193–1194, fig. 4.136.— Lowry 2000: 325 (list).—Escobar- Briones et al. 2002: 367 (list).— Vinogradov et al. 2004: 16, 24 (table).— Brusca & Hendrickx 2005: 151 (list).— Zelickman 2005: xvii (list), fig. 44a-b (pp. 274–277).— Browne et al. 2007: 819 (table), fig. 4 (phylogenetic tree).— Gasca 2007: 118 (table).— Garcia-Madrigal 2007: 155, 192 (list).— Costa et al. 2009: 103, 198, fig. 188.— Gasca 2009a: 89 (table).— Gasca et al. 2009: 1497, 1501 (tables).— Valencia & Giraldo 2009: passim.— Valencia & Giraldo 2012: 1493 (table).—Hurt et al. 2013: 31 (table), figs 1, 2 (phylogenetic).— Zeidler 2016: 47 (key).— Copilaş-Ciocianu et al. 2020: fig. 1 (phylogenetic).— Espinosa-Leal et al. 2021a: passim.— Espinosa-Leal et al. 2021b: passim.

Type material. Type material of Schnehagenia rapax could not be found in any major European museum and is considered lost. Claus (1887) provides a figure of a mature male (about 10 mm) but does not illustrate P5 or P6 which best characterise species of Brachyscelus . Claus (1887) does not document any other specimens and no precise type locality is given, just “Vom Capit. Schnehagen am Cap gefangen”, probably off the Cape of Good Hope.

Material examined. In NHMD: S.W. Indian Ocean, Galathea station 217 [14°20’S 45°09’E], one male. Gulf of Panama, Galathea station 745 [07°15’N 79°21’W], one female. In SAM: S.W. Indian Ocean, off South Africa , Meiring Naude station SM 13 [27°18.5’S 33°05’E], 274–0 m, juvenile male; station SM 14 [27°30.6’S 32°50.6’E], 247–0 m, juvenile male; station SM 155 [30°24.5’S 31°32.5’E], surface, immature female & male, 2 juveniles; station SM 222D [32°37.3’S 29°14.7’E], 193–0 m, immature female. In SAMA: N.E. Pacific, Alaska Gyre [50°0.5’N 165°0.2’W], 150 m, 2 males; N.W. of Vancouver Island [48°58.05’N 130°40.03’W], 1200–0 m, one female. Tasman Sea, off eastern Tasmania, 2 females, 2 males (4 lots) .

Diagnosis. Body length up to 10 mm for males, slightly less for females (?). Head relatively small in females, depth about twice length; more globular, sometimes produced to slight, rounded point in males, length almost equal to depth. Antennae 2 of males; length terminal article about 0.3 x preceding one. Gnathopod 1 basis relatively slender, slightly shorter than for G2, with distinct pocket for A 2 in males; carpus with antero-distal corner not produced in females, in males produced into rounded lobe, partly overlapping propodus or sometimes absent as in females; carpal process with large teeth with few, minor serrations; postero-distal corner of propodus with two large teeth followed by 2–3 smaller teeth on posterior margin; dactylus relatively sharp, length about half of propodus. Gnathopod 2 similar to G1 but basis without pocket and antero-distal corner of carpus not produced. Pereopods 3 and 4 morphologically similar, P4 marginally longer than P3; merus slightly inflated anteriorly, length about 0.4 x basis in females, marginally longer in males; carpus slightly longer than merus in females, equal in length in males; propodus slightly longer than carpus in females, about 1.3 x carpus in males, with slightly serrated posterior margin. Pereopod 5 slightly longer than P6; basis oval-shaped, length 1.6 x maximum width, without antero-distal lobe, with small, rounded postero-distal lobe; merus about 0.3 x basis length, slightly shorter than carpus; propodus marginally longer than carpus; dactylus relatively long, slightly more than 0.3 x propodus. Pereopod 6 basis almost ovalshaped, widest proximally, length about 1.5 x maximum width, with narrow, pointed antero-distal lobe produced to two-thirds of ischium, posterior margin with rounded distal margin but not produced into postero-distal lobe; merus slightly inflated antero-distally, length about 0.4 x basis, much longer than carpus, about, 1.4 x in females and 2 x as long in males; propodus similar in length to merus; anterior margin of merus (distally), carpus and propodus with small serrations; dactylus relatively long, 0.4–0.5 x propodus length. Pereopod 7 basis with posterior margin inflated proximally, length about 1.5 x maximum width in males, slightly narrower in females, slightly longer than remaining articles combined; merus slightly longer than carpus; propodus slightly shorter than carpus, with complex projections on antero-distal corner; dactylus hook-shaped, partly retractile. Uropod 1 with relatively long peduncle; endopod only marginally longer than peduncle and exopod. Uropod 2 endopod 1.3 x peduncle length, slightly longer than exopod. Uropod 3 endopod about 3.0 x peduncle length, slightly longer than endopod, without distinct excavation on inner margin. Rami of all uropods with serrated margins. Double urosomite much wider than long (1.4 x in females, almost 1.6 x in males). Telson of females slightly shorter than width at base; relatively longer and narrower in males, slightly longer than width at base, apex rounded.

Remarks. This species was inadequately described by Claus (1871, 1879, 1887) and his later illustration ( Claus 1887) omits some important characters, especially details of pereopod 6, the basis of which is a useful character to distinguish species of Brachyscelus . Thus, B. rapax might be considered a species of doubtful status. The only subsequent record of B. rapax by Barnard (1932), prior to Vinogradov et al. (1982, 1996), represents B. rapacoides (specimens examined). Barnard (1940), Siegfried (1963), and Dick (1970) also refer to this record. Vinogradov et al. (1982, 1996) recognise the validity of B. rapax but regard B. rapacoides a junior synonym and illustrate a specimen of B. rapacoides . As a result, subsequent authors referring to this reference, to make their species determinations, may also have confused the two species and some of the above records could be erroneous. Thus, while the true identity of B. rapax might be in doubt the specimens listed above are most similar to B. rapax as described and illustrated by Claus rather than any other species. In particular the morphology of the gnathopods, pereopod 7 and urosomite are very similar, although in the male illustrated here (fig. 12) the carpus of gnathopod 1 lacks the rounded antero-distal lobe overlapping the propodus, but this may be a variable character because it is present in other male specimens (fig. 11). The basis of pereopods 5 and 6 is not very clear in the illustration of Claus (1887) but seem to be rounded without any large lobes, unlike B. crusculum or B. globiceps . Also, the head of males of the latter species is rounded. Similarly, both sexes of B. macrocephalus have a relatively large, rounded head and the basis of pereopod 6 has a relatively large rounded antero-distal lobe. Thus, the above specimens (listed) and B. rapax , as described by Claus, are most similar to B. rapacoides but can be distinguished from it as detailed under that species. In conclusion B. rapax ( Claus, 1871) is here retained as a valid species, based on the specimens examined, because they differ from all the other known species and most closely match Claus’s description of this species. Nomenclatural stability is best served by taking this action rather than relegating Claus’s name to a nomen dubium and describing my specimens as new to science.

Distribution. Based on literature records, some of which may be based on mis-identifications. A rare species, found mainly in tropical waters. In the Atlantic it has been found off South Africa in the south, and near the Cape Verde Islands and the Sargasso Sea in the north. In the Pacific it has been recorded from the South China Sea and the tropical eastern part including the Tasman Sea. In the Indian Ocean it is only known from the south-western region. The record of Zelickman (2005), from the Mediterranean Sea, most likely represents B. rapacoides .

Figures

FIGURE 11. Brachyscelus rapax (Claus, 1871). Female 4.8 mm. Tasman Sea of Tasmania [44°12.3’S 147°14.11’E], near surface. Head, G1, G2 from male 8.1 mm. N. Pacific, Alaska Gyre [50°05’N 165°02’W], 150 m. Scale bars: 0.5 mm (habitus, male G1–2); 0.2 mm (female G1–P7, Us).

FIGURE 12. Brachyscelus rapax (Claus, 1871). Male 7.6 mm. Tasman Sea off Tasmania [44°12.05’S 147°24.4’E], near surface. Scale bars: 0.1 mm (A1); 1.0 mm (A2); 0.5 mm (remainder).