Brachyscelus rapacoides Stephensen, 1925

Zeidler, Wolfgang, 2021, A review of the hyperiidean amphipod family Brachyscelidae Stephensen, 1923 (Crustacea: Amphipoda: Hyperiidea), Zootaxa 5026 (3), pp. 405-439 : 422-426

Brachyscelus rapacoides Stephensen, 1925

( Figs 9–10 )

Brachyscelus rapacoides Stephensen, 1925: 179–180 , 230 (table), figs 67–68.— Barnard 1930: 432.— Pirlot 1930: 27, fig. 7.— Pirlot 1939a: 47.— Pirlot 1939b: 70.— Hurley 1955: 181 (key).— Reid 1955: 26.— Vinogradov 1962: 24.— Hure et al. 1969: 603 (table).— Dick 1970: 69, fig. 13 (part).— Tashiro & Jossi 1972: fig. 8 (map), 20 (list), 35 (table).— Brusca 1973: 9 (table), 19.— Harbison et al. 1977: 471.— Laval 1980: 20 (table).— Zeidler 1992: 115 (key), 117–119, fig. 21.— Gasca & Shih 2001: passim.— Lima & Valentin 2001: 473 (list), 476 (table).— Escobar-Briones et al. 2002: 367 (list).— Gates et al. 2003: 302.—Gasca 2004: 997 & 998 (tables).— Gasca 2007: 118 (table).— Gasca 2009a: 89 (table).— Gasca 2009b: 66 (table).— Gasca 2009c: 218 (table).— LeCroy et al. 2009: 969 (table).— Zeidler & De Broyer 2009: 64.— Mori et al. 2010: 6 & 10 (lists).—Gasca et al. 2012: passim.— Gasca & Franco-Gordo 2014: 76 (list).— Zeidler 2016: 47 (incl. key).— Puente-Tapia et al. 2018: passim.— Zeidler et al. 2018: passim.— Hereu et al. 2020: passim.

Brachyscelus atlantideus Reid, 1955: 26–28 , fig. 6.— Shih & Chen 1995: 181 (regarded a synonym of B. rapax ).

Brachyscelus rapax [mis-identification, part].— Barnard 1932: 292 (two of three specimens).— Barnard 1940: 520; Siegfried 1963: 6; and Dick 1970: 69 all list Barnard’s 1932 record.— Vinogradov et al. 1982 /1996: 396/489 (key), 400/493–495, fig. 215 ( B. rapacoides regarded a synonym of B. rapax ; fig. 215 is of B. rapacoides ).

Brachyscelus rapax [probable mis-identification].— Shih & Chen 1995: 178 (key), 181–182, fig. 118.— Lin et al. 1996: 231 (table).— Vinogradov 1999: fig. 4.136.— Lowry 2000: 325 (list).— Zelickman 2005: fig. 44a-b (pp. 274–277).— Costa et al. 2009: 103, 198, fig. 188.

Type material. The syntypes (13 specimens) of Brachyscelus rapacoides are in the NHMD, in alcohol. The type locality is the Mediterranean Sea, in the general region of the Ionian Sea, Thor station 183 [37°52’N 23°09’E], surface, 16 March 1910 ( NHMD- 86563; formerly CRU-9055); stations 282, 283 [38°12’N 15°37’E], 40 metres of wire out, 8 and 13 March 1911 ( NHMD- 86564–5; formerly CRU-9056–7) and station 743 [34°26’N 20°08’E], surface, 23 September 1913 ( NHMD- 85778; formerly CRU-7934). Stephensen (1925) illustrates a male (4–4.5 mm) and a female (3–3.5 mm) from station 743; partly dissected and labelled “Type”.

Type material of synonyms. The syntypes (about 55 specimens, mainly juveniles) of Brachyscelus atlantideus are in the NHMD, in alcohol. The type locality is the tropical Atlantic , off Freetown , Sierra Leone, Atlantide station 141, near surface, 9 April 1946 and off Guinea [09°20’N 14°15’W] ( NHMD-83552 ; formerly CRU-5708) and Atlantide station 145, near surface, 13 April 1946 ( NHMD-86562 ; formerly CRU-9054). An examination of this material has confirmed the synonymy .

Material examined. Type material of B. rapacoides and B. atlantideus as detailed above and the following. In AM: Tasman Sea, east of Port Jackson [33°52’S 151°37’E], 55– 18 m, one male (P39858). In Canadian Museum of Nature : tropical Atlantic , just west of Barbados , one male . In NHM: S. Atlantic, Discovery station [25°47’S 14°48’W], 2 females, 1 male (1936.8.1.750) . S. Pacific near New Zealand, Terra Nova station 109, one male (1936.11.2.3258) . In SAM: S.W. Indian Ocean, off South Africa, Meiring Naude station SM 147D [30°16’S 31°24.5’E], 212–0 m, one female and station SM 189S [34°04.3’S 27°10’E], 50 m, one female. In SAMA: Mediterranean Sea, off Israel [31.83°N 34.64°E], 7 females, 3 males, 1 juvenile (C12253). S.W. Atlantic, off Brazil [23°46.1’S 44°02’W], surface, one female . Gulf of Mexico [19°34’03”N 87°20’04”W], 2 females . Coral Sea, Great Barrier Reef, 2 females, 4 males, 5 juveniles (6 lots). N.E. Indian Ocean, off northern Western Australia, Ningaloo Reef , 2 females, 13 males (4 lots).

Diagnosis. Body length up to 5.0 mm for females and 6.0 mm for males. Head globular in females, depth about 1.7 x length; produced to rounded point in males, depth about 1.5 x length. Body of females more plump than for other congeners approaching that of Hyperia and Hyperoche . Antennae 2 of males with terminal article about halflength 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 produced into small lobe, partly overlapping propodus, especially in males; carpal process with large teeth interspersed with 1–3 smaller teeth; postero-distal corner of propodus with two large teeth followed by several 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 0.3 x basis for females, almost 0.4 x basis for males; carpus 1.4–1.6 x merus length, about 0.8 x propodus; propodus with slightly serrated posterior margin. Pereopod 5 slightly longer than P6; basis oval-shaped, length 1.7–1.8 x maximum width, without antero-distal lobe; merus about 0.3 x basis length, about 0.7 x carpus; propodus about 1.3 x carpus length; dactylus relatively short, slightly more than 0.2 x propodus. Pereopod 6 basis almost pear-shaped, widest proximally, length 1.5–1.6 x maximum width, with narrow, pointed antero-distal lobe produced to two-thirds of ischium, also with rounded postero-distal lobe reaching to limit of ischium; merus slightly inflated antero-distally, length about 0.3 x basis (slightly more for males), slightly longer than carpus; propodus marginally longer than carpus; anterior margin of merus (distally), carpus and propodus with small serrations; dactylus relatively long, about 0.5 x propodus in males, slightly longer in females, with few setae on anterior margin. Pereopod 7 basis with posterior margin inflated proximally, length about 2 x maximum width, slightly longer than remaining articles combined; merus almost 0.7 x carpus length; propodus sub-equal in length to carpus, with complex projections on antero-distal corner; dactylus hook-shaped, partly retractile. Uropod 1 with relatively broad peduncle; endopod 1.5 x peduncle length for females, 1.2 x peduncle for males; exopod about 1.2 x peduncle length. Uropod

2 endopod almost 2 x peduncle length for females, slightly less for males; exopod about 1.3 x peduncle length. Uropod 3 endopod 3.0 x peduncle length for females, 4.0 x peduncle for males; endopod of males slightly more broadened distally, with slight excavation terminally on inner margin; exopod slightly shorter than endopod. Rami of all uropods with serrated margins. Double urosomite slightly more than 1.7 x wider than long. Telson of females slightly longer than width at base; relatively longer and narrower in males, length about 1.3 x width at base, apex slightly pointed or rounded.

Remarks. This is a relatively small species, reaching maturity at about 5.0–6.0 mm, or less. It is similar to B. rapax and has been considered a synonym of this species by some authors in the past (e.g., Vinogradov et al. 1982, 1996), but has been demonstrated to be a valid species by Zeidler et al. (2018). It is distinguished from B. rapax by the following characters: i) in males the fifth article of the second antennae is about half as long as the fourth (about one quarter for B. rapax and all other congeners); ii) the carpus and propodus of the gnathopods are armed with long teeth interspersed with 1–3 smaller ones (only minor serrations on or between larger teeth in B. rapax ); iii) the basis of pereopod 7 is much longer than the remaining articles combined and the merus is distinctly shorter than the carpus; iv) the peduncle of uropod 1 is relatively short and broad (slender and only slightly shorter than the endopod in B. rapax ); and v) the telson is distinctly longer than wide and the apex is more pointed (only marginally longer than wide in B. rapax with very rounded apex). Also, B. rapax is a much larger species reaching maturity at about 10 mm.

An unusual character of this species is that the body of females is relatively plump, approaching that of Hyperia and Hyperoche whereas females of all other congeners are relatively slender, like males. Also, in male specimens examined, the eyes, when viewed dorsally, become widely separated anteriorly, unlike other species in which the eyes are only separated by a narrow margin, almost to the tip of the rostrum ( Zeidler 1992). Thus, this character could also be of specific significance if it proves to be consistent throughout its range.

Brachyscelus rapacoides has been recorded with Hydromedusae, and the medusae Aequoria sp. , Orchististoma sp. and Leuckartiara sp. , as well as with the pteropod Diacavolinia longirostris ( Blainville, 1821; previously in Cavolinia ) ( Harbison et al. 1977). More recently it has been recorded with the scyphozoan Chrysaora lactea Eschscholtz, 1829 and the hydrozoan Olindias sambaquiensis F. Műller, 1861 by Puente-Tapia et al. (2018). Zeidler et al. (2018) record it from the Scyphozoan, Rhopilema nomadica Galil, 1990 , introduced to the Mediterranean Sea through the Suez Canal ( Galil et al. 1990).

Distribution. This is a relatively rare species, known from widely separated records, from tropical and temperate regions of all the world’s oceans, including the Mediterranean Sea. In the Atlantic it has been recorded from about 44°N to tropical regions off Africa and Brazil, including the Caribbean and Gulf of Mexico. In the Indian Ocean it is known from one record, south of Australia ( Vinogradov 1962) and from off north Western Australia (SAMA specimens). In the Pacific it has been recorded from the Indo-Pacific region and the Tasman Sea, including the region just north of New Zealand, with one doubtful record from Hawaii. Most catches are from near-surface waters.

Figures

FIGURE 9. Brachyscelus rapacoides Stephensen, 1925. Female 4.4 mm (ovig.), SAMA C12253. Mediterranean Sea, off Israel [31.8°N 34.6°E], 5–15 m, on jellyfish Rhopilema nomadica Galil, 1990. Scale bars: 0.5 mm (habitus); 0.1 mm (A1); 0.2 mm (remainder). (Reproduced from Zeidler et al., fig. 4).

FIGURE 10. Brachyscelus rapacoides Stephensen, 1925. Male 5.4 mm, SAMA C12253. Mediterranean Sea, off Israel [31.8°N 34.6°E], 5–15 m, on jellyfish Rhopilema nomadica Galil, 1990. Scale bars: 0.5 mm (habitus); 0.2 mm (remainder). (Reproduced from Zeidler et al., fig. 5).