Pronoe Guérin-Méneville, 1836

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 : 19-22

Genus Pronoe Guérin-Méneville, 1836

( Figs 3–4 )

Pronoe Guérin-Méneville, 1836: 6 .— Milne-Edwards 1838: 307.— Lucas 1840: 239 –240.— Milne-Edwards 1840: 71 (key), 98–99.— Dana 1852: 316.— Dana 1853: 1009, 1015.— Bate 1862: 336 –337.— Claus 1879: 23 (key), 23–25.— Claus 1880: 588.— Gerstaecker 1886: 484.— Claus 1887: 48 (key), 48–50.— Stebbing 1888: 1507.— Spandl 1927: 216 (key).— Pirlot 1929: 147.— Bowman & Gruner 1973: 42 (key), 42–43.— Vinogradov et al. 1982: 361 (key), 369.— Shih & Chen 1995: 146 (key), 147.— Vinogradov 1999: 1202 (key), 1204.

Type species. Pronoe capito Guérin-Méneville, 1836 , by monotypy. A syntype male (9.5 mm) is in the ANSP (CA2674), Guérin-Méneville Collection no. 454 (see Zeidler 1997a). Spamer and Bogan (1992, 1994) list this specimen as a holotype, and although this may be all that remains of Guérin-Méneville’s original material, it is clear that he had more than one specimen at the time of description for he says, “Plusieurs individus de ces Crustacés nous ont été donnés par M. Gay ”. Therefore, the specimen must be regarded a syntype. It is also likely that the figures of this species, given by Guérin-Méneville (1836), represent more than one specimen, because his figure “3a” could be that of a specimen with the head missing. Despite being dry, the specimen is in remarkably good condition, and there is no difficulty in determining the diagnostic features that characterise the genus Pronoe . The type locality is the south-east Pacific Ocean, off Chile.

Diagnosis. Body shape robust or globular. Head round. 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 moderately enlarged, oval callynophore, with aesthetascs arranged in two-field brush medially; with two smaller articles inserted on antero-dorsal corner. Antennae 1 of females with 3-articulate peduncle; callynophore narrowly rectangular; with two smaller articles inserted terminally. Antennae 2 inserted adjacent to buccal mass; in males consisting of large, quadrate basal article, followed by five elongate articles, folded only once and placed in groove next to mandibular palp, and partly under A1; in females reduced to basal article like that of male. Mandibular palp 3-articulate in both sexes. 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 elongate, curled, bifid lobes. Maxillae 2 consisting of slightly curled, quadrate lobes with tiny denticles terminally; with small medial palp. Maxilliped with inner lobes not fused; medial margin of outer lobes without fringe of setae or membranous fringe. Gnathopoda simple. Pereopods 3 & 4 distinctly shorter than pereopods 5 & 6. Pereopod 5; basis about twice as wide as merus; may overlap with P6 but non-locking; articles 3–7 inserted 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. Pereopod 7 reduced in size with large, quadrate basis, with only 1–3 terminal articles. Uropoda all with articulated endopoda and exopoda, all lanceolate, usually with serrated margins.

Species. Pronoe capito Guérin-Méneville, 1836 .

Sexual dimorphism. The sexes are remarkably similar in gross morphology, differing mainly in the morphology of the antennae. Females tend to have a more rounded head, and in males the gnathopoda are more robust, and armed with relatively more setae.

Remarks. This is a very distinctive, monotypic genus. It differs most significantly from all other platysceloideans in that females have a 3-articulate mandibular palp. The only other platysceloidean genus in which females have a mandibular palp is Tryphana , but in that genus the palp is reduced to two articles. The maxillae are also relatively well developed, and their morphology is unique amongst the Platysceloidea, and hyperiideans in general. The medial palps on the second maxillae are extraordinary. At first it was thought that they might be an artefact of dissection, but careful manipulation revealed that they are indeed palps, attached medially near the base of the ‘outer plate’. They are somewhat analogous to the inner plate found in the Gammaridea, but nothing like it has been found in any other hyperiidean. It seemed plausible that the maxillae might have been confused because first maxillae, with palps, occur in some hyperiidean families. However, careful manipulation of mouthparts, of intact specimens, confirmed the initial observation, which is supported by the illustrations of this species by Claus (1887) and Stebbing (1888).

Pronoe also differs from most other platysceloideans in that the second antennae of males are reduced in size, and the articles are not folded back on one another. In this respect it resembles Thamneus , but in that genus the second antennae of males are also reduced in the number of articles, and they are curved near the buccal mass, and do not extend forward underneath the head, as in Pronoe .

Amongst the specimens examined there are small males and females (<6.0 mm) with the mandibular palp not fully developed. Also one large female (10.9 mm), has second antennae as illustrated here ( Fig. 3 ), but with a small additional article on the anterior corner of the large, fleshy article.

Pronoe capito seems to be a rare species, and until recently ( Shih & Chen 1995) a description or figure of the female was unknown. Consequently nothing is known regarding its biology. Most of the specimens, examined in museum collections, are males suggesting that females may occupy a slightly different ecological niche, probably more closely associated with gelatinous plankton, as found for most other hyperiideans. However, a gelatinous host, if there is one, remains to be recorded.

Pronoe has been found in the tropical warm-temperate parts of the Atlantic, Indian (including Arabian and Red Sea) and Pacific oceans. It seems to prefer surface waters (<200 m).

Figures

FIGURE 3. Pronoe capito Guérin-Méneville, 1836, female (10.8 mm), Tasman Sea, AM P 39849; male (11.6 mm), Indian Ocean, off South Africa, SAMA C 5807. A, B, habitus and ventral view of female; C, head of male; D, E, medial view of Mx 2 and ventral view of Mx 1 & 2 of female. Scale bars = 1.0 mm (A – C), 0.5 mm (Us), 0.2 mm (remainder).

FIGURE 4. Pronoe capito Guérin-Méneville, 1836, female (10.8 mm), Tasman Sea, AM P 39849; male (11.6 mm), Indian Ocean, off South Africa, SAMA C 5807. Scale bars = 0.5 mm.