Cranocephalus Bovallius, 1890

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 : 96-99

Genus Cranocephalus Bovallius, 1890

( Figs 47–48 )

? Carcinornis Costa, 1864: 88.

Cranocephalus Bovallius, 1890: 47 (key), 94–95.— Spandl 1927: 179 (key).— Yoo 1971: 64 (key).— Bowman & Gruner 1973: 49 (key), 51.— Vinogradov et al. 1982: 404 (key), 429.— Nair 1995: 6 (key), 17.— Shih & Chen 1995: 190 (key), 202.— Vinogradov 1999: 1196 (incl. key).

Stebbingella Bovallius, 1890: 47 (key), 97–98.— Spandl 1927: 179 (key).— Pirlot 1929: 167.

Type species. Cranocephalus goesi Bovallius, 1890 by monotypy. Type material (male, 8 mm) could not be found at the NRS, ZMUC or in Upsala and is considered lost. However, it is clear from Bovallius’s (1890) description and figures that his species is a junior synonym of Oxycephalus scleroticus Streets, 1878 . However , this species does not belong to the current concept of Oxycephalus and so Cranocephalus is maintained as a valid genus to accommodate it. No precise type locality is given for C. goesi , just “the tropical regions of the Atlantic ”.

Type material of Oxycephalus scleroticus (female and three males, 10–15 mm) could not be found in any major North American institution and is considered lost. Specimens were collected from the North Pacific by W.H. Jones from three locations [26°13’N 143°15’W; 25°13’N 143°15’W & 25°50’N 132°45’W], all from the surface.

Type species of synonyms. The type species of Carcinornis is C. acutirostris Costa, 1864 , by page priority . Type material could not be found in any Italian or major European institution and is considered lost. Costa’s description is too brief to enable a generic or specific determination of this species but Stebbing (1888) considered his second species, C. inflaticeps , to be “suggestive of Oxycephalus typhoides Claus ” which is currently regarded a synonym of Cranocephalus scleroticus , and this is the currently accepted, although very doubtful, status for Costa’s species. The type locality is the Mediterranean Sea, Gulf of Naples .

Stebbingella was instituted by Bovallius (1890) for Oxycephalus scleroticus Streets, 1878 , but this species is considered a senior synonym of Cranocephalus goesi . Bovallius was most likely unaware of the variation in the morphology of the head, which is characteristic of this genus, thus adding to the confusion.

Diagnosis. Body shape robust or globular. Head oval. Rostrum distinctly elongate, pointed. Eyes occupying most of head surface except for rostrum; grouped in one field on each side of head. Antennae 1 of males with 2- articulate peduncle; flagellum with large, crescent-shaped callynophore, with relatively large antero-distal lobe, with aesthetascs arranged in two-field brush medially, with three smaller articles inserted below antero-dorsal corner. Antennae 1 of females without 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 to pereonite 2; basal article elongate, sub-equal in length to following article; terminal article very short, not folded, pointing posteriorly. Mandibular palp 3-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 all partly fused with pereonites; coxa 5 usually with lateral spinous process. Gnathopods 1 & 2 chelate or sub-chelate; carpal process knife-shaped, armed with prominent teeth only. Pereopods 3 & 4 sub-equal in length to pereopods 5 & 6. Pereopod 5 & 6 with very broad basis, with bulging posterior margin, but not operculate, not overlapping with opposing pereopoda; articles 3–7 inserted terminally to basis. 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 2–5. Gills on pereonites 2–6; all with folds.

Species. Cranocephalus scleroticus (Streets, 1878) .

Sexual dimorphism. Apart from obvious morphological differences in the antennae and mandibles, males tend to have a slightly larger head, especially in mature specimens. Fage (1960) lists other differences (all minor ) in relative lengths of the body and appendages.

Remarks. This genus is readily distinguished by the morphology of the head, body, gnathopoda, pereopoda and urosome. Additional distinctive characters are the strongly, calcified cuticle, and the distinctive pores found on the basis of pereopods 5–7, which also occur on the pereonites and pleonites. The fifth coxae also usually have a strong, backward projecting, spinous process, a character not found in any other oxycephalidean.

Cranocephalus is unusual in the development of the head. In juveniles the head is globular with a relatively short, sharp rostrum which becomes larger and longer in adults. A failure to appreciate these changes in development may have led to some past errors in identification.

Amongst the family Oxycephalidae , Cranocephalus does not closely resemble any other genus. The morphology of the male antennae is most like that of Calamorhynchus and Streetsia . The first antennae of females are reduced to three articles, as is sometimes found in Rhabdosoma , but differ in their morphology. The first maxillae are very small, and the second maxillae are absent, as in Calamorhynchus and Leptocotis . The simple maxillipeds are most like those of Rhabdosoma , and also approach those of Oxycephalus and Calamorhynchus .

Cranocephalus is currently considered to be monotypic ( Fage 1960, Vinogradov et al. 1982), and all nominal species are considered synonyms of C. scleroticus (Streets, 1878) . However, C. thai Sudara, 1975 may be a valid species because two key characters, a rounded rostrum and the carpus of gnathopod 2 with a serrated posterior margin (like G1), are atypical of C. scleroticus .

There are very few records of associations with gelatinous plankton. It has been found with the ctenophores, Pleurobranchia sp. (Harbison et al. 1977) and species of the order Cydippida ( Harbison et al. 1978) .

Fage (1960) provides some biogeographical information regarding C. scleroticus . It seems to be epipelagic in habit, and is widespread in tropical regions of the world’s oceans, but has not been recorded from the Red Sea.

Figures

FIGURE 47. Cranocephalus scleroticus (Streets, 1878), male (14.4 mm), N. E. Indian Ocean, near Ningaloo Reef, Western Australia, SAMA C 5927. A, habitus. Scale bars = 1.0 mm (A), 0.5 mm (remainder).

FIGURE 48. Cranocephalus scleroticus (Streets, 1878), male (14.4 mm), N. E. Indian Ocean, near Ningaloo Reef, Western Australia, SAMA C 5927 (G 1 & 2); female (8.1 mm) and male (6.3 mm), Indian Ocean, off South Africa, SAMA C 5814. Scale bars = 0.1 mm (Mx 1, Mxp), 0.2 mm (remainder).