Pallenopsis vanhoeffeni Hodgson, 1915

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 : 526-527

Pallenopsis vanhoeffeni Hodgson, 1915

Pallenopsis vanhoffeni Hodgson, 1915, p. 145 .— Child 1995, pp. 150–151

Pallenopsis vanhöffeni . — Hodgson, 1927, pp. 336–337, Fig. 9.— Calman 1915, p. 43.— Gordon 1938, pp. 17–18, Figs. 3b , 4a , 5c, 6c–d; 1944, p. 45.— Marcus 1940, p. 23.— Hedgpeth 1950, p. 151.— Fage 1952a, p. 184; 1952b, pp. 269–270.

Pallenopsis vanhoeffeni . — Arnaud, 1972, p. 148.— Krapp 1980, p. 6.— Nielsen et al. 2009, p. 1150 (list.).—Munilla & Soler- Membrives 2015, p. 422 (list).

Pallenopsis vanchoffeni . — Pushkin, 1993, pp. 265–267, Fig. 262.— Gutt et al. 2000, p. 71 (list).

Pallenopsis gaussiana Hodgson, 1915, p. 145 .

Pallenopsis setigera Hodgson, 1915, p. 146 .

Material examined. BECA (P.0001) one larvigerous male, Victoria Land Transect cruise ( Italica XIX), Cape Hallett , stn. H-out 4 bis, 72°18.4' S 170°26.7' E, 234 m depth, Van Veen, 12 Feb 2004 .

Diagnosis. Proboscis cylindrical, straight. Cephalic segment with a small bump on antero-lateral part. Three anterior trunk segments with two dorsal groups of long slender setae. Lateral processes more separated distally. Chelae fingers touching when closed along their entire length, no setose pad at base of movable finger. Palp in contact with basal oviger processes. Legs with long setose setae mainly placed on dorsal and lateral surfaces, arranged in rows. Auxiliary claws shorter than half claw length.

Geographical and bathymetric distribution. Child (1995) and Pushkin (1993) summarised the geographic and bathymetric information concerning this species. Pallenopsis vanhoeffeni is considered circumpolar. The known bathymetric range is 3–889 m in depth ( Munilla & Soler-Membrives 2009). Our specimen does not modify the known information about the geographical and bathymetric distribution of this species.

Remarks. Pallenopsis vanhoeffeni is close to other setose species of the genus, P. hodgsoni and P. pilosa , with broad, wedge shaped chelae fingers, touching when closed but without a setose pad on the movable finger.

However characters such as the long setae of the three long articles arranged in rows, on dorsal and lateral surfaces, or the presence of the small latero-proximal bump on the cephalic segment may be used to easily distinguish P. vanhoeffeni (see also the Discussion part of P. rotunda n. sp. in this paper).

Remarks on Antarctic and Sub-Antarctic species of Pallenopsis . Child's identification key (1995), the most recent key for identification of species of Pallenopsis from Antarctic and Sub-Antarctic waters, included ten species, while Munilla & Soler-Membrives (2009) listed 18 species, increasing the number of taxa in this genus from that biogeographic area. However, some of the species listed are incompletely described or known, and in several cases, species boundaries are not clear, mainly due of a lack of knowledge concerning character variability. These facts make clear the strong need for a detailed taxonomic study of the Pallenopsis species from this area we start addressing by providing an update to Child’s key more than two decades later.

Stock (1975) proposed a new subgenus, Bathypallenopsis , with diagnostic characters such as chelifores with fingers equal or longer than the palm, curved, slender, gaping when closed, and oriented in prolongation of the palm, no spiny cushion on the movable finger, or auxiliary claws absent or small. While characteristics of the subgenus Pallenopsis retained the presence of fingers shorter than the palm, broad, wedge-shaped, meeting when closed, often not oriented in prolongation of the palm, spiny cushion present, and auxiliary claws usually present. Later, Bamber (2007) raised the subgenus Bathypallenopsis to generic rank, however, species with intermediate characters were also described: e.g. P. lateralia Child, 1995 has long auxiliary claws and typical fingers of Bathypallenopsis , but they are placed perpendicularly to the palm, or P. villosa Hodgson, 1907 , placed in the subgenus Pallenopsis by Child (1995) who considered most characters consistent with the diagnostic characters of the latter subgenus, despite Stock (1975) including it in Bathypallenopsis .

Munilla & Soler-Membrives (2009) on their check-list of Pallenopsis species for Antarctic and Sub-Antarctic waters did not consider the genus Bathypallenopsis or any subgenus Rank in Pallenopsis . In the same way, we only consider the genus Pallenopsis in our proposed key, without any grouping at subgenera level.

The number of species in our proposed key reaches 24. We have included the more recently described new species, as well as some not listed by Munilla & Soler-Membrives (2009) but accepted as valid by other authors, such as Pallenopsis meridionalis Hodgson, 1914 , P. hodgsoni , and P. hiemalis .

According to Child (1995) and Stock (1975) Pallenopsis meridionalis is an imperfectly known species. The description provided by Hodgson (1927: 337) is based on a damaged specimen, and it was not illustrated. Additional information about this species is contradictory (see Pushkin 1975, 1993, Child 1995).

Pallenopsis hodgsoni has been considered a synonym of P. pilosa by several authors, but as commented above, both species have differential characters (see Remarks on P. hodgsoni in this paper).

Pallenopsis hiemalis is close to P. patagonica and has long been a controversial species. Authors such as Child (1995), Munilla & Soler-Membrives (2009) or Bamber et al. (2018) consider this species as a synonym of P. patagonica , but other authors (such as Gordon 1932 or Pushkin 1975; 1993) consider P. hiemalis as a valid species. Gordon (1932) examined a large number of specimens of P. patagonica (about 62) and she considered that only the type specimen of P. hiemalis has differential characters to be distinguished from P. patagonica : the size and arrangement of propodus spines, the tubercle of the lateral processes, and the relatively developed palps. Later, in the same way, Gordon (1944) pointed out that the propodus of P. hiemalis has no “heel” but has spines along its entire ventral surface. Pushkin (1975; 1993) described this species using newly captured specimens and he adds the armature of the 7 th and 8 th articles of the walking legs, suggesting that these structures are different to those of all other members in the genus.

We propose a dichotomous key as a practical tool, in order to facilitate the identification of Pallenopsis species from Antarctic and Sub-Antartic waters. We have attempted to avoid subjective expressions or sexual dimorphism characters and include precise characters or ranges of variation with discriminatory value.

Figures

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).