Streetsia Stebbing, 1888

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 : 93-96

Genus Streetsia Stebbing, 1888

( Figs 45–46 )

Streetsia Stebbing, 1888: 1603 .— Bovallius 1890: 46 (key), 80.— Spandl 1927: 179 (key), 184.— Pirlot 1929: 164.— Barnard 1940: 542 (key).— Hurley 1955: 182 (incl. key).— Yoo 1971: 64 (key).— Bowman & Gruner 1973: 49 (key), 53.— Zeidler 1978: 30 (key), 35.— Vinogradov et al. 1982: 404 (key), 412–413.— Nair 1995: 6 (key), 19–20.— Shih & Chen 1995: 190 (key), 215.— Vinogradov 1999: 1195 (key), 1198.

Oxycephalus (part)— Claus 1879: 43.— Claus 1887: 68.

Type species. Streetsia challengeri Stebbing, 1888 by monotypy. The unique, holotype female is in the NHM (89.5.15.324), on three microscope slides. The type locality is the north-western Pacific, east of Japan [35°35’N 150°50’E], between Challenger stns. 239 & 240, surface, 20 June 1875.

Type species of synonyms. Some species assigned to Oxycephalus by Claus (1879, 1887) clearly belong with Streetsia .

Diagnosis. Body shape elongate and narrow. Head oval. Rostrum distinctly elongate. 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, elongate, 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 with 3-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 to pereonite 1; basal article elongate, sub-equal in length to following article; terminal article, 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 lobes with terminal denticles. Maxillae 2 absent. Maxilliped with inner lobes completely fused; medial margin of outer lobes with membranous fringe. Coxae all separate from pereonites. Gnathopod 1 sub-chelate; carpal process knife-shaped, armed with prominent teeth and setae. Gnathopod 2 chelate or sub-chelate; carpal process knife-shaped, armed with prominent teeth and setae. Pereopods 3 & 4 sub-equal in length to pereopods 5 & 6. Pereopod 5; basis elongate, relatively broad, about 5 x as wide as merus; with articles 3–7 inserted terminally to basis. Pereopod 6 with relatively broad basis, especially proximally, but not operculate, does not overlap, or lock, with opposing pereopod; 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. Streetsia steenstrupi ( Bovallius, 1887) ; S. porcella ( Claus, 1879) ; S. challengeri Stebbing, 1888 ; S. mindanaonis ( Stebbing, 1888) and S. palmaspinosa Vinogradov, 1990 .

Sexual dimorphism. Some species exhibit more sexual dimorphism than others. For example, mature females of S. challengeri have gnathopod 2 with the postero-distal corner of the basis expanded into a triangular lobe; a character not found in males or any other species of Streetsia . In S. mindanaonis the head of females have a slight neck, and in males the head has a slight dorsal depression, just posterior to the eyes, although it is not always well developed. Generally the head of males is relatively shorter, and there are minor variations in the setation of the gnathopoda, and morphology of the pereopoda.

Remarks. Species of this genus are readily distinguished by the long, barrel-shaped head, which is produced into a sharp rostrum.

Streetsia most closely resembles Leptocotis in general habit, but in the morphology of the male antennae, mandibles, and maxilliped, it is more like Calamorhynchus . The first antennae of females are similar to Tullbergella , in that the callynophore has a slight bulge. The first maxillae are relatively large with a group of tubercles terminally, unlike other genera of Oxycephalidae . In having the coxae not fused with the pereonites it resembles Leptocotis , Glossocephalus (fused with pereonite 7) and Tullbergella .

The fifth pereopods of Streetsia have a long, spinose structure on the medial surface of the coxae, similar to that found in Leptocotis . It does not seem to function as a means of articulation with the sixth pereopoda, as the pereopoda are too far apart on the pereon to allow for articulation.

As with other genera of Oxycephalidae , Streetsia is preferentially associated with ctenophores, although recorded associations are few. Juveniles have been found with the ctenophore Leucothea pulchra (SAMA specimens), and S. porcella has been recorded with radiolarian colonies, marine snow, and the ctenophores, Leucothea sp. (Harbison et al. 1977), L. multicornis and Eurhamphaea vexilligera ( Harbison et al. 1978) . In addition, Lavaniegos & Ohman (1999) found S. steenstrupti associated with the pteropod Corolla spectabilis and Gasca et al. (2014) found Streesia sp. on the ctenophore Thalassocalyce inconstans .

Fage (1960) provides considerable biogeographical information regarding this genus. Most species seem to be epipelagic in habit, preferring tropical to sub-tropical waters. He recognised four species, and one other has been described by Vinogradov (1990).

Figures

FIGURE 45. Streetsia challengeri Stebbing, 1888, female (29.5 mm), N. E. Pacific, off California, SAMA C 5924 (A, Us); from Tasman Sea, female (40.0 mm) and male (32.0 mm), SAMA C 4223 (A 1 - f, A 2 - m), and male (32.0 mm), SAMA C 5818 (A 1 - m, mouthparts). A, habitus of female SAMA C 5924. Scale bars = 2.0 mm (A), 1.0 mm (A 2, Md, Us), 0.2 mm (A 1), 0.1 mm (Mx 1, Mxp).

FIGURE 46. Streetsia challengeri Stebbing, 1888, female (29.5 mm), N. E. Pacific, off California, SAMA C 5924. Scale bar = 0.5 mm.