Glossocephalus rebecae, Zeidler, Wolfgang & Browne, William E., 2015

Zeidler, Wolfgang & Browne, William E., 2015, A new Glossocephalus (Crustacea: Amphipoda: Hyperiidea: Oxycephalidae) from deep-water in the Monterey Bay region, California, USA, with an overview of the genus, Zootaxa 4027 (3), pp. 408-424 : 418-421

Glossocephalus rebecae sp. nov.

( Figs. 7–9 )

Glossocephalus sp. — Browne et al. 2007: 819 (list), fig. 4 (phylogenetic tree). Hurt et al. 2013: 31 (table), figs. 1–2 (phylogenetic trees). Gasca et al. 2014: 4 (table), 7, fig. 2.

Material examined. Holotype: Female (4.8 mm), Monterey Bay, California [36°42’N 122°04’01.2”W], ROV Ventana, Dive 2716 D8, from R/V Point Lobos, 568 m, SHD Haddock, 6 September 2005. USNM 1268612. Associated with the ctenophore Bathocyroe fosteri Madin & Harbison, 1978 ( Fig. 8 ). In vivo photograph of this specimen also reproduced by Gasca et al. (2014, fig. 2).

Paratype: Juvenile female, Monterey Bay, California [36°41’55.2”N 122°03’25”W], ROV Tiburon, Dive 847 DS4, from R/V Western Flyer, 557 m, SHD Haddock, 11 April 2005. USNM 1268613. Associated with the ctenophore Bathocyroe fosteri .

Other records: Because this species is easily recognisable, the following records from photos and video footage are regarded as reliable records for this species. All were recorded with the ctenophore Bathocyroe fosteri .

Male ( Fig. 9 ); Monterey Bay region (36.60°N 127.37°W), ROV Tiburon, Dive 2768 T851, from R/V Western Flyer, 541 m, 4 June 2005. Associated video footage: tape 3 FID 0 2.47.0 4. In vivo photograph also reproduced by Gasca et al. (2014, fig. 2).

Female; Monterey Bay (34°41’45.6”N 122°04’58.8”W), 728 m, 21 February 2007.

Two adults and several juveniles; same locality as above but at 830 m depth, 21 August 2007.

Description of holotype. Female 4.8 mm, probably near maturity judging by development of oostegites. Head as long as first four pereonites combined, with short, sharp rostrum, more or less triangular in shape with slight, or negligible, neck. Eyes composed of distinctly pigmented, crescent-shaped, retina, occupying about one-quarter of back half of head, with crystalline cones orientated anteriorly and laterally. Pereon cylindrical, length about 1.6 x pleon. Pleonites 1–2 with slight excavation on postero-distal corner. Pleonite 3 with slight excavation on distal margin and rounded postero-distal corner. Gnathopoda relatively small, barely reaching past basis of P3. Gnathopod 1; basis slightly shorter than remaining articles combined, relatively narrow; merus relatively short, about 0.2 x basis, width about 1.7 x length; carpus quadrate, width about 1.3 x length, somewhat spoon-shaped, barely projecting under propodus, produced into strong terminal tooth medially, armed with three or four strong setae near outer postero-distal corner; propodus sub-quadrate, as long as carpus, with slightly serrated distal margin, forming weak sub-chela with carpal process; dactylus slightly curved, length about two-thirds of propodus. Gnathopod 2 marginally longer than G1, similar in structure except carpus is relatively longer and carpal process extends slightly further under propodus. Pereopods 3 & 4 relatively slender, similar in structure. Pereopod 3 slightly shorter than P4, about 0.8 x P5; basis length slightly more than twice merus; carpus, about 1.4 x merus; propodus slightly longer than carpus; dactylus length about 0.2 x propodus. Pereopod 5 with normal articles (not particularly widened), all with smooth margins; length 1.2 x P6; basis length about twice merus; carpus marginally longer than merus; propodus length about 1.5 x carpus; dactylus length about 0.2 x propodus. Pereopod 6 marginally shorter than P4; anterior margin of merus, carpus and propodus with fine serrations; basis length about twice merus; carpus length 0.7 x merus; propodus length 1.4 x carpus; dactylus length almost 0.4 x propodus. Pereopod 7; basis oval-shaped, length about 1.4 x width, slightly shorter than remaining articles combined; merus and carpus of similar length, propodus slightly longer; dactylus very small. Uropod 1; peduncle reaching beyond limit of peduncle of U2, to limit of U3; outer ramus slightly wider than inner, length about twice inner ramus, about 0.8 x peduncle. Uropod 2; peduncle reaches just short of base of peduncle of U3; inner ramus slightly longer than peduncle, about 1.3 x outer ramus. Uropod 3; peduncle very short, slightly wider than long; inner ramus length about 1.5 x outer ramus, 3.0 x peduncle. Telson triangular, rounded, marginally longer than wide, reaching to about two-thirds of inner ramus of U3. Margins of rami and telson finely denticulate.

Colour: from in situ / vivo photographs and video footage. Eyes orange, digestive cecal organs often bright red (perhaps representing material ingested from host ctenophore tissue or more likely material harvested from the colloblast lined tentacles of the host feeding apparatus). The remainder of the animal is relatively translucent.

Etymology. This species is named for Rebeca Gasca, ECOSUR-Chetumal, Mexico in recognition for her work on the hyperiidean fauna of Mexican waters and for her help in procuring specimens of this new species.

Remarks. This is a most unusual species with very distinctive eyes that seem to have evolved in response to living in meso- and bathypelagic depths. Apart from the eyes it is also distinguished from its congener, G. milneedwardsi , by the following characters. The head is more triangular in shape, with a pointed rostrum; the gnathopoda are of a slightly different structure, more or less sub-chelate; pereopods 3 & 4 are not particularly slender, and the merus is the second shortest article, not the second longest; the articles of pereopods 5 & 6 are not especially broad or paddle-like, and only the anterior margins of the merus, carpus and propodus of pereopod 6 are armed with fine serrations; pereopods 3–6 have relatively longer dactyls; the postero-distal corners of pleonites 1– 2 are not pointed but have a slight excavation, and there are minor variations in the relative lengths of the articles of the uropoda. Based on observations, it also seems to be a relatively small species, with most specimens observed to be around 5 mm in length. Unfortunately, the male specimen cited by Browne et al. (2007) ( Fig. 9 ) could not be located, thus a detailed description of the male of the species is still required.

To date this species has only been observed in association with the ctenophore Bathocyroe fosteri , a mesopelagic species that seems to be common on the mid-Atlantic Ridge. Thus, one might expect that G. rebecae would also be found in the Atlantic. However, Madin & Harbison (1978), who described this ctenophore from the northwestern Atlantic, off New Jersey, from several specimens collected or observed in depths of about 200–980 m, specifically mention that there were no associated amphipods present. It is possible that this species has evolved from a surface form, like G. milneedwardsi , in the north-east Pacific and is now confined there. The alternate hypothesis that surface living species evolved from the deep-water form is rejected on the basis that all other members of the family Oxycephalidae are primarily surface living species.

Distribution. Known only from the Monterey Bay region, California, from depths of 541–830 m, associated with the ctenophore Bathocyroe fosteri , as detailed above.

Figures

FIGURE 7. Glossocephalus rebecae sp. nov. Holotype female 4.8 mm (USNM 1268612), NE Pacific, Monterey Bay, California (36 ° 42 ’ N 122 ° 04 ’ 01.2 ” W), ROV, 568 m. Scale bars = 0.2 mm (Us), 0.5 mm (remainder).

FIGURE 8. Glossocephalus rebecae sp. nov. in vivo photograph of holotype female on its host, the ctenophore Bathocyroe fosteri.

FIGURE 9. Glossocephalus rebecae sp. nov. in vivo photograph of male from Monterey Bay region (36.60 ° N 127.37 ° W), ROV Tiburon, Dive 2768 T 851, from R / V Western Flyer, 541 m, 4 June 2005. Associated video footage: tape 3 FID 0 2.47. 0 4.