Glossocephalus Bovallius, 1887

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 : 409-410

Genus Glossocephalus Bovallius, 1887

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: 18. Shih & Chen 1995: 190 (key), 200. Vinogradov 1999: 1196 (incl. key).

Elsia Giles, 1890: 249 –250.

Type species. Glossocephalus milneedwardsi Bovallius, 1887 by page priority. Type material could not be found at the Zoologisk Museum, University of Copenhagen, Denmark ( ZMUC), but the Swedish Museum of Natural History (Naturhistorika Riksmuseet), Stockholm, Sweden ( NRS), has one male specimen ( SMNH 8706) in three pieces, labelled “No. 3690. Atlanten 15°N 20°W”, and a microscope slide of the second antennae of another male specimen ( SMNH 8707) labelled “ 10°22’N 21°16’W ”, which probably represents type material used by Bovallius (1890) for his illustration of the species (pl. 5, fig. 5).

Type species of synonyms. The type species of Elsia is E. indica Giles, 1890 . Type material could not be found at The Natural History Museum, London, UK (NHM) and is considered lost. However, the description and figures provided by Giles clearly represent a species of Glossocephalus .

Diagnosis. Body elongate and narrow. Head with small rounded, or sharp rostrum, not longer than first four pereonites. Eye field occupying most of head surface, alternatively screening retinal pigments may appear as pair of crescent-shaped clusters, occupying about one-quarter of back half of head. Male antenna 1 with one-articulate peduncle; callynophore large, crescent-shaped, with small antero-distal lobe and with aesthetascs arranged in onefield brush medially; with three distal articles inserted on antero-dorsal corner. Female antenna 1 with twoarticulate peduncle, narrowly rectangular callynophore, and two smaller terminal articles. Antenna 2 absent in females. Male antenna 2 five-articulate; with strong zig-zagged articulation, and all but terminal article folded back on each other, under head, extending ventro-anteriorly and ventro-posteriorly between the gnathopoda and pereopoda. Mandibular palp absent in females; one-articulate in males. Mandibular molar reduced or absent. Mandibular incisor relatively broad, straight, with several teeth, with small distal lobe medially. Maxilla 1 reduced in size to single, small rounded lobe. Maxilla 2 absent. Maxilliped with inner and outer lobes separate; inner lobes completely fused, reaching to about half-length outer lobes; medial margin of outer lobes with membranous fringe; peduncle with two small humps near base of outer lobes. Pereonites all separate; first two very narrow, together equal in length to third. Coxa 7 fused with pereonite, remainder free. Gnathopoda relatively small, chelate; carpal process some-what spoon-shaped, ending in sharp tooth, usually armed with few strong setae. Pereopods 3–7 simple. Pereopods 3 & 4 slightly shorter than, or about as long as, P5; sometimes P3 & 4, especially P3, longer than P5. Pereopod 5 longer than P6 but similar in structure, in some specimens the articles can be relatively broad and paddle-like, with a relatively small dactylus. Pereopod 7 reduced in size, with enlarged basis; all articles present. Uropoda all with free exopoda, and endopoda; usually with serrated margins. Telson fused with double urosomite, shorter than U3. Oostegites on pereonites 3–5. Gills on pereonites 2–6 in females, 3–6 in males.

Species. Glossocephalus milneedwardsi and G. rebecae sp. nov.

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 & 6 sometimes have slightly broader articles.

Remarks. This genus is readily distinguished within the Oxycephalidae 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 Oxycephalidae . In particular the mandibular palp in males consists of a single article, with a rounded lateral process ( Fig. 4 ). 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. It should be noted though that there is evidence suggesting that article length of the mandibular palp may be a particularly labile trait among the Amphipoda ( Browne and Patel 2000) and thus, while useful for discriminating between species, is a homoplastic character of limited value for inferring phylogenetic relationships. 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. 4 ) 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 female first antennae, Rhabdosoma and Leptocotis in the morphology of the second male antennae, and all other genera, except Oxycephalus and Rhabdosoma , in the presence of first maxillae.

Figures

FIGURE 4. Glossocephalus milneedwardsi Bovallius, 1887. Mouthparts from female 12.5 mm (SAMA C 5816); same data as fig. 3. Mouthparts and antennae (A 1 with aesthestascs removed) from male 8.0 mm (SAMA C 5815), NW Atlantic (38 ° N 67 ° W), scuba near surface, on the ctenophore Bolinopsis rubrapunctatus. Scale bars = 0.1 mm (A 1), 0.2 mm (A 2), 0.05 mm (mouthparts).