Eupronoe Claus, 1879

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 : 24-27

Genus Eupronoe Claus, 1879

( Figs 5–6 )

Eupronoe Claus, 1879: 23 (key), 26–28.— Gerstaecker 1886: 484 –485.— Claus 1887: 48 (key), 50–52.— Stebbing 1888: 1509.— Chevreux & Fage 1925: 425.— Spandl 1927: 216 (key).— Pirlot 1929: 147.— Hurley 1955: 174 (key), 175.— Yoo 1971: 61 (key).— Bowman & Gruner 1973: 42 (key), 43.— Zeidler 1978: 21 (key), 21–22.— Vinogradov et al. 1982: 361 (key), 362.— Shih & Chen 1995: 146 (key), 148.— Vinogradov 1999: 1203 (incl. key).

Type species. Eupronoe maculata Claus, 1879 by page priority. Type material could not be found at the MFN or ZMH and is considered lost. However , the description and figures provided by Claus (1879, 1887) readily characterise this genus. The type locality is the tropical south-west Indian Ocean, off Zanzibar .

Diagnosis. Body shape robust or globular. Head round. Rostrum only present in males, short and rounded. Eyes occupying most of head surface; grouped in one field on each side of head. Antennae 1 of males with 3- articulate peduncle; flagellum with large, crescent-shaped callynophore, with aesthetascs arranged in one-field brush medially; with three smaller articles inserted on antero-dorsal corner. Antennae 1 of females with 3-articulate peduncle; flagellum with narrowly rectangular callynophore; with two smaller articles inserted terminally. Antennae 2 inserted on ventral surface of head in groove. Antennae 2 of males 5-articulate; strongly zig-zagged, with most articles folded back on each other; extending anteriorly under head and posteriorly into antennal pocket of gnathopod 1; basal article elongate, sub-equal in length to following article; terminal article very short, not folded, pointing posteriorly. Antenna 2 of females 5-articulate. Mandibular incisor relatively broad, with several teeth, with small distal lobe medially; in male orientated at right angles to palp. Maxillae 1 consisting of elongate, lobes, with four rounded teeth distally on medial margin. Maxillae 2 consisting of relatively broad lobes, pointed distally, with rounded medial bulge. Maxilliped with inner lobes completely fused; medial margin of outer lobes with fringe of closely packed slender setae. Gnathopod 1 sub-chelate; basis with antennal pocket in male, with fold of articles 2 & 3 of antennae held in pocket; carpal process rounded, armed with microscopic teeth or setae. Gnathopod 2 chelate; carpal process knife-shaped, armed with microscopic teeth or setae. Pereopods 3 & 4 distinctly shorter than pereopods 5 & 6. Pereopod 5; basis about 3 x as wide as merus; may overlap with P6 and lock proximally; articles 3–7 inserted terminally, or almost sub-terminally, to basis. Pereopod 6; basis very broad, more than 5 x as wide as merus, but not operculate; articles 3–7 inserted sub-terminally on basis; merus with antero-distal corner extended, distinctly overlapping carpus medially. Pereopod 7 reduced in size with large basis, with only 1–3 terminal articles. Uropoda all with articulated exopoda and endopoda. Uropod 2; endopod and exopod leaf-like, foliaceous with smooth margins. Uropod 3; endopod, and sometimes also exopod, leaf-like, foliaceous, with smooth margins.

Species. Eupronoe maculata Claus, 1879 ; E. armata Claus, 1879 ; E. minuta Claus, 1879 ; E. intermedia Stebbing, 1888 and E. laticarpa Stephensen, 1925 .

Sexual dimorphism. Apart from the morphology of the mandibles, the antennae, and the antennal pocket of gnathopod 1, males differ from females in having a slightly more pointed head, the carpus of gnathopod 1 is generally broader, and the carpal process of gnathopod 2 ends in a sharper point. Females also tend to have a more robust pereon.

Remarks. In all species, the coxa of pereopod 5 articulates proximally with the coxa/basis of pereopod 6, as in Parapronoe . Similarly all species have a weak, ridge/groove locking mechanism near the proximal, anterior corner of the ischium of pereopods 5 & 6, and pleonites 1–3 have a slight lateral ridge, that lines up with the posterior margin of pereopod 6, when the animal is curled. Also, like Parapronoe , the cuticular sculpture is relatively prominent, consisting of circular markings or pits, or dorso-ventral striations; characters which can be used to help distinguish species.

Virtually nothing is known about the biology of species, but they seem to be associated with salps, or siphonophores, or both. Eupronoe maculata has been recorded with salps ( Spandl 1927), and E. minuta has been found associated with the siphonophores, Agalma elegans (Harbison et al. 1977) , Apolemia uvaria , and Sulculeolaria quadrivalvis ( Laval 1980) and Rosacea cymbiformis ( Gasca et al. 2014), and has also been found with the salp Thalia democratica ( Young & Anderson 1987—misidentified as E. armata ).

Eupronoe is widely distributed in tropical and warm-temperate regions of the world’s oceans and can, at times, be relatively abundant in plankton hauls near the surface ( Stephensen 1925, Pirlot 1939).

Species of Eupronoe are particularly difficult to determine with certainty because of the sexual dimorphism, morphological changes due to growth, and moulting, and the lack of adequate illustrations in the literature. Zeidler ( 1992 a, 1998) gives more information on all species, together with some illustrations. Vinogradov et al. (1982) recognise four species; to this should be added E. intermedia Stebbing, 1888 , which Tashiro (1978) demonstrated to be a valid species, distinguished from E. armata Claus, 1879 .

Figures

FIGURE 5. Eupronoe maculata Claus, 1879, female (8.0 mm) and male (7.7 mm), Indian Ocean, off South Africa, SAMA C 5812. A, habitus of male. Mouthparts from male. Scale bars = 1.0 mm (A), 0.2 mm (A 1 & 2 - m), 0.1 mm (remainder).

FIGURE 6. Eupronoe maculata Claus, 1879, female (8.0 mm) and male (7.7 mm), Indian Ocean, off South Africa, SAMA C 5812. Scale bars = 0.2 mm.