Pallenopsis hodgsoni Gordon, 1938

Cano-Sánchez, Esperanza & López-González, Pablo J., 2019, Two new species and new findings in the genus Pallenopsis (Pycnogonida: Pallenopsidae) with an updated identification key to Antarctic and Sub-Antarctic species, Zootaxa 4585 (3), pp. 517-530 : 525-526

Pallenopsis hodgsoni Gordon, 1938

Pallenopsis pilosa, Hodgson, 1907, p. 15 , Pl. 2, Fig. 2 .— Bouvier 1911, p. 1139; 1913, p. 107, Figs. 60–61.— Calman 1915 (part), p. 42.— Gordon 1932, p. 87.

Pallenopsis hodgsoni Gordon, 1938 , pp. 16–17, Figs. 3a , 4d , 5d; 1944, p. 45.— Hedgpeth 1950, p. 151.— Munilla 1991, pp. 31– 32, Fig. 14.— Child 1995, pp. 142–143.— Munilla & Soler-Membrives 2015, p. 422 (list).

Material examined. MNA (11031) one female, Victoria Land Transect cruise ( Italica XIX), Cape Hallett, stn. Hin 4, 72°17.1’ S 170°14.0’ E, 196 m depth, Van Veen, 16 Feb 2004 .

Diagnosis. Proboscis cylindrical, straight. Three anterior trunk segments with two dorsal groups of long slender setae. Lateral processes separated by not more than half their own diameter, U-shaped (between second and third segment). Chelae finger touching when closed along its entire length, no setose pad at base of movable finger. Legs with long setose setae mainly placed on dorsal and lateral surfaces, not arranged in rows. Auxiliary claws shorter than half main claw length.

Geographical and bathymetric distribution. Child (1995) summarized the geographical and bathymetric information concerning this species. Although most of the specimens are known from the Ross Sea, there are also some other scattered Antarctic records. For these reasons, P. hodgsoni is considered circumpolar. This species has a wide depth range, 120–2450 m. Our specimen does not modify the known information about the geographical or bathymetric distribution of this species.

Remarks. P. hodgsoni is a controversial species throughout the different contributions in the literature. Some authors considered this species a synonym of P. pilosa ( Hoek, 1881) ( Turpaeva 1974; Pushkin 1993; Munilla & Soler-Membrives 2009), while other studies considered it as a valid species ( Child 1995; Munilla & Soler- Membrives 2015; Bamber et al. 2018).

Gordon (1938) proposed P. hodgsoni as a different species from P. pilosa . She based the necessity of that description on the important differences observed by Calman (1915) in his specimens assigned to P. pilosa from the Ross Sea, and her own observations. Characters such as a more robust body, lateral processes separated by half their own diameter or less, auxiliary claws about 1/3 claw length, the structure of the long setose setae on the walking legs, or the diameter of the proximal part (in females) of the second coxa of the walking legs, were considered enough to distinguish it as a separate species. Moreover the material identified as P. pilosa by Hodgson (1907) was also considered by Gordon as belonging to her new species.

As discussed above, P. pilosa and P. hodgsoni seem to be closely related species. Although we have observed variability in some characters (our specimen has the auxiliary claws longer than one-third of the claw), we agree with the criteria of Calman (1915) and Gordon (1938) and their separation of these as two distinct species. Child (1995) pointed out that the chelae fingers are very short in P. hodgsoni , shorter than palm width, but in our specimen they are slightly longer than palm width. The diagnosed set of characters here proposed for P. hodgsoni include the information provided by the latter authors as well as the variability observed in our specimen.

Figures

FIGURE 2. Pallenopsis gracilis sp. nov. Holotype, male. A Third leg, right; B Cement gland tube (detail from A); C Palm + Chela of chelifore; D Palp; E Distal third leg articles; F Oviger (due to fixed position of articles in this appendage, apparent proportions in the illustration could not reflect real relations, see text for full measurements and ratios). Scale bars: 6 mm (A); 0.5 mm (C, D); 1 mm (F, E).

FIGURE 3. Pallenopsis rotunda sp. nov. Holotype, male. A Dorsal view (showing the relative size and distribution of spines); B lateral view. Scale bars: 3 mm (A, B).

FIGURE 4. Pallenopsis rotunda sp. nov. Holotype, male. A Third leg, right; B Cement gland tube (detail from A); C Palm + Chela of chelifore; D Palp; E Distal third leg articles; F Male oviger (due to fixed position of articles in this appendage, the number of articles and apparent proportions in the illustration could not reflect real relations, see text for full measurements and ratios); G Female strigilis. Scale bars: 3 mm (A); 1 mm (C, E, G); 0.5 mm (D); 2 mm (F).