Glossocephalus Bovallius, 1887

Zeidler, Wolfgang, 2016, A review of the families and genera of the superfamily PLATYSCELOIDEA Bowman & Gruner, 1973 (Crustacea: Amphipoda: Hyperiidea), together with keys to the families, genera and species, Zootaxa 4192 (1), pp. 1-136 : 86-89

Genus Glossocephalus Bovallius, 1887

( Figs 41–42 )

Glossocephalus Bovallius, 1887: 35 .— Bovallius 1890: 47 (key), 105.— Chevreux & Fage 1925: 432 –433.— Spandl 1927: 179 (key), 196.— Barnard 1940: 542 (key).— Pillai 1966: 171 (key).— Yoo 1971: 63 (key).— Bowman & Gruner 1973: 49 (key), 51–52.— Zeidler 1978: 30 (key), 34.— Vinogradov et al. 1982: 404 (key), 427.— Nair 1995: 6 (key), 18.— Shih & Chen 1995: 190 (key), 200.— Vinogradov 1999: 1196 (incl. key).— Zeidler & Browne 2015: 409 –410. Elsia Giles, 1890: 249 –250.

Type species. Glossocephalus milneedwardsi Bovallius, 1887 by page priority. Type material could not be found at the ZMUC, but the NRS has one male specimen (no. 8706) in three pieces, labelled “No 3690 Atlanten 15°N 70°W” (designated lectotype by Zeidler & Browne 2015), and a microscope slide of the second antennae of another male specimen labelled “ 10°22’N 21°16’W ” (no. 8707), which probably represents type material used by Bovallius (1890) for his illustration of the species (pl. 5, fig. 5). Bovallius (1887, 1890) only provides a general locality, “tropical region of the Atlantic” and mentions that he had both male and female specimens.

Type species of synonyms. The type species of Elsia is E. indica Giles, 1890 by monotypy. Type material could not be found at the NHM and is considered lost. However, the description and figures provided by Giles clearly represent a species of Glossocephalus . The type locality is the Arabian Sea, Bombay Harbour, Investigator expeditions, A. Carpenter Commanding.

Diagnosis. Body shape elongate and narrow. Head globular around eyes, not longer than first four pereonites, with small rounded, or sharp, rostrum. Eye field occupying most of head surface; grouped in one field on each side of head, or screening retinal pigments grouped in crescent-shaped cluster occupying about one-quarter of back of head. Antennae 1 of males with 1-articulate peduncle; flagellum with large, crescent-shaped callynophore, with small antero-distal lobe, with aesthetascs arranged in one-field brush medially; with three smaller articles inserted on antero-dorsal corner. Antennae 1 of females with 2-articulate peduncle; callynophore narrowly rectangular, with two smaller articles inserted terminally. Antennae 2 absent in females. Antennae 2 of males 5-articulate; strongly zig-zagged, with most articles folded back on each other; extending anteriorly under head and posteriorly between the gnathopoda and pereopoda to pereonite 1; basal article elongate, sub-equal in length to following article; terminal article, short, not folded, pointing posteriorly. Mandibular palp 1-articulate in males. Mandibular incisor relatively broad, with several teeth, with small distal lobe medially; in male orientated more or less parallel to palp. Maxillae 1 consisting of rounded plates. Maxillae 2 absent. Maxilliped with inner lobes completely fused; medial margin of outer lobes with membranous fringe. Coxae 7 fused with pereonite. Gnathopoda relatively small, chelate, or G1 almost sub-chelate; carpal process some-what spoon-shaped, ending in sharp tooth, conspicuously smooth or armed with few strong setae. Pereopods 3–7 simple. Pereopods 3 & 4 distinctly longer, or only slightly shorter, than P5. Pereopod 5 slightly longer than P6 but similar in structure, in some species the articles can be relatively broad and paddle-like, with a relatively short dactylus. Pereopod 7 reduced in size with large basis; all articles present; dactylus normal. Uropoda all with articulated exopoda and endopoda, all lanceolate, usually with serrated margins. Telson fused with double urosomite. Oostegites on pereonites 3–5. Gills on pereonites 2–6 in female, 3–6 in male; all without folds.

Species. Glossocephalus milneedwardsi Bovallius, 1887 and G. rebecae Zeidler & Browne, 2015 .

Sexual dimorphism. Apart from obvious morphological differences in the antennae and mandibles, males have a more elongate (less globular) head; gills are absent on pereonite 2, and pereopods 5 and 6 have slightly broader articles than in females.

Remarks. This genus is readily distinguished by the morphology of the rostrum, gnathopoda, pereopoda and urosome.

Glossocephalus has a number of unusual morphological characters that distinguish this genus from other members of the family Oxycephalidae . In particular the mandibular palp in males consists of a single article, with a rounded lateral process. In all other genera of the superfamily Platysceloidea, males have a 3-articulate mandibular palp, and in all other genera of the family Oxycephalidae the first article of the mandibular palp is exceptionally elongate. Additional characters that distinguish Glossocephalus are the first antennae of males that are similar to those of Amphithyrus and Thamneus rather than any other oxycephalids; the morphology of the maxilliped ( Fig. 42 ) is unique, in that the peduncle has two small humps near the base of the outer lobes, and the inner lobe has a distinct, medial invagination; pereopods 5 & 6 are sometimes paddle-like, or slender, and the basis is not especially enlarged, as is characteristic of other Platysceloidea; the seventh pair of coxae are fused with the pereonite as in the Parascelidae and most Platyscelidae ; males have the gills absent on pereonite 2, and the rostrum is not much longer than found in some other genera of Platysceloidea. Although these unique characters, collectively, might suggest that Glossocephalus does not belong with the Oxycephalidae , molecular phylogenetic studies by Browne et al. (2007) and Hurt et al. (2013) strongly support the placement of Glossocephalus as nested well within the Oxycephalidae . However, additional molecular analyses of genera in the family will be useful for accurately assessing the relationship of Glossocephalus to other lineages of oxycephalids.

Amongst the family Oxycephalidae , Glossocephalus resembles Oxycephalus , Leptocotis and Calamorhynchus in the morphology of the first antennae of females; Rhabdosoma and Leptocotis in the morphology of the second antennae of males, and all other genera, except Oxycephalus and Rhabdosoma , in the presence of first maxillae.

Glossocephalus has, to date, only been recorded in association with ctenophores; G. milneedwardsi with Deiopea kaloktenota ( Krumbach 1911, Steuer 1911a, b), Bolinopsis vitrea (Harbison et al. 1977, 1978), Leucothea multicornis , Cestum veneris ( Harbison et al. 1978) , L. multicornis , Beroe ovata ( Laval 1980) , L. pulchra and Bolinopsis rubrapunctatus (SAMA specimens), and G. rebecae only with the mesopelagic ctenophore Bathocyroe fosteri (see Zeidler & Browne 2015).

Fage (1960) provides some information on the biology of Glossocephalus milneedwardsi , and demonstrated that it occurred most frequently in the top 100 m, was fairly abundant down to 200 m, but very infrequent below that depth. It seems to be relatively uncommon, but is widely distributed in, mainly, tropical regions of the world’s oceans. Glossocephalus rebecae is only known from the Monterey Bay region of California, in depths of 540– 830 m .

Figures

FIGURE 41. Glossocephalus milneedwardsi Bovallius, 1887, female (10.2 mm), N. E. Pacific, off California, SAMA C 5816. A, habitus. Scale bars = 1.0 mm (A), 0.2 mm (G 1 & 2), 0.5 mm (remainder).

FIGURE 42. Glossocephalus milneedwardsi Bovallius, 1887, female (10.2 mm), N. E. Pacific, off California, SAMA C 5816; male (8.0 mm), N. W. Atlantic, SAMA C 5815. Scale bars = 0.2 mm (A 2), 0.1 mm (A 1), 0.05 mm (mouthparts).