New findings and two new species of the genus Pallenopsis (Pycnogonida: Pallenopsidae) from the Southern Ocean

Taxonomy

Material examined: MZB (2024-3776) holotype, one adult female, Polarstern cruise ANT XXIII/8, stn. 670–1. W King George Island, South Shetland Islands, Antarctica, 61°51.69’S 59°15.43’W, 263.0–270.3 m depth, bottom trawl, 1 January 2007.

Fig. 3 Pallenopsis tubercula n. sp. Holotype, female. A, dorsal view (showing the relative size and distribution of spinules); B, lateral view. Scale bars: 3 mm (A, B) 

Fig. 4 Pallenopsis tubercula n. sp. Holotype, female. A, third leg, right; B, distal third leg articles; C, palm + chela of chelifore; D, palp; E, 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: 4 mm (A); 1 mm (B, C, D, E). 

Diagnosis. Proboscis straight, slightly widened distally. Cephalic segment not tapering anteriorly, with a small bump on each side of the ocular tubercle. Lateral processes separated by more than half their own diameter. Chelae fingers touching proximally when closed; movable chelae finger with little marked pad. Palps longer than wide, not in contact with basal oviger process. Walking legs without long setae (long setae = subequal or longer than the diameter of the article) on the three longest articles. Femur the longest article of the walking legs. Auxiliary claw longer than half main claw length.

Description of the holotype (female). Size moderate, leg span 148.8 mm. Proboscis mostly cylindrical, distal third slightly widened, provided with short spines.

Trunk fully segmented, with lateral processes widely separated, more than half their own diameter. Segments with fine short spines mainly on the dorsal rounded elevation. Segments first, second and third ventrally bulky. Lateral processes with fine short spines mainly on a pair of dorso-distal tiny tubercles. Fourth segment shorter than third segment. Cephalic segment flattened dorsally, not tapering anteriorly, and with a short spine on a small latero-proximal bump on the cephalic segment (on either side of ocular tubercle).

Abdomen long, down-curved, with minute spines on entire surface, and slightly widened on its distal third.

Ocular tubercle at anterior part of cephalic segment, taller than wide and topped by a rounded, slightly forward-tilted cone. Four eyes of similar size, anterior pair slightly lower than posterior pair.

Chelifores large, first escape article shorter than second, first escape article slightly raised dorso-distally and second wider distally. Chela palm longer than wide, with an inner lateral band of short setae. Fingers shorter than the width of the palm, placed more or less perpendicular to palm, smooth and touching when closed. Base of movable finger with a little marked pad with low minute setae.

Palps one-articled, longer than wide. Inserted distinctly separated from oviger basal process.

Oviger nine-articled. Third article strongly curved, fourth article is the longest and eighth article is the shortest. Last fourth articles with short setae distally.

Legs with minute spines along entire length. Second coxa shorter than sum of first and third coxae length, with increasing density of minute spines distally. Femur the longest article. Tibiae 2 with longer spines ventro-distally. Tarsus short, with ventro-distal long spines. Propodus slightly curved, slightly broader proximally with three long heel spines in a row, with heterogeneous random spines along the half distal sole. Main claw shorter than half propodus length; auxiliary claw longer than half main claw length. Sexual pores located ventrally on second coxa of all four legs.

Measurements of holotype (mm). Length of trunk (tip of the cephalic segment to the tip of fourth lateral processes): 13.8. Width of trunk across second lateral processes: 10.0. Length of cephalic segment: 7.0. Length of proboscis: 5.0. Basal diameter of proboscis: 2.5. Greatest diameter of proboscis: 2.7. Length of abdomen: 4.6. Length of left chelifore scape: 6.9. Length of articles of chelifore: first 3.2, second 3.7. Length of left palm: 2.8. Length of left chelae: 1.7. Length of left palp: 1.4. Length of third left leg: 69.4. Length of articles of leg 3: coxa 1 2.5, coxa 2 5.5, coxa 3 4.0, femur 18.5, tibia 1 14.4, tibia 2 17.7, tarsus 1.0, propodus 4.1, claw 1.7, auxiliary claws 1.2. Length of left oviger: 9.78. Length of oviger articles (1st to 9th): 0.89, 1.3, 1.35, 2.05, 1.49, 0.95, 0.81, 0.43, 0.51.

Distribution. At present, Pallenopsis tubercula n. sp. is known from its type locality at South Shetland Islands, at a depth of 130.7–144.3 m.

Etymology. The specific name derives from tuberculum (L.), referring to the small dorso-distal tubercles of the lateral processes and the small latero-proximal bumps on the cephalic segment (on either side of the ocular tubercle).

Remarks. Recently, two species have been described, P. aulaeturcarum Dömel and Melzer, 2019DömelJ.S., MacherT., DietzL., et al.2019. Combining morphological and genomic evidence to resolve species diversity and study speciation processes of the Pallenopsis patagonica (Pycnogonida) species complex. Front Zool16: 36. 10.1186/s12983-019-0316-y and P. obstaculumsuperavit Dömel and Melzer, 2019DömelJ.S., MacherT., DietzL., et al.2019. Combining morphological and genomic evidence to resolve species diversity and study speciation processes of the Pallenopsis patagonica (Pycnogonida) species complex. Front Zool16: 36. 10.1186/s12983-019-0316-y, with dorso-distal thickenings on the lateral processes. However, both species have a combination of diagnostic characters that allows them to be easily differentiated from others. Pallenopsis aulaeturcarum has a triangular-shaped setose pad whose entire length is attached to the chela, abdomen orientated upwards and setae on the ventral and dorsal sides of the trunk. On the other hand, P. obstaculumsuperavit has a triangular-shaped setose pad but only attached to the chela by its basal half, abdomen pointing downwards and the second and third coxa with a set of setae on the ventral side as a brush. This set of characters is not shared by the new species of Pallenopsis proposed here.

Pallenopsis tubercula n. sp. is comparable to P. hiemalis Hodgson, 1907HodgsonT.V.1907. Pycnogonida. National Antarctic Expedition 1901-1904. Reports of the National Antarctic expedition of 1901-1904. Nat. Hist.3: 1-172., P. buphtalmus Pushkin, 1993PushkinA.F.1993. The pycnogonida fauna of the South Ocean. Biological results of the Soviet Antarctic expeditions. Russ. Acad. Sci. Exp. Fauna Seas.20: 1-397. and P. gracilis Cano-Sánchez and López-González, 2019Cano-SánchezE., López-GonzálezP.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. Zootaxa4585: 517-530. 10.11646/zootaxa.4585.3.7, as they share the following set of characters: (1) chelae wedge-shaped, fingers touching proximally when closed; (2) without long setae on the three longest articles of walking legs; (3) movable chelae finger with setose pad; (4) palp longer than wide; (5) similar separation of lateral processes on proximal and distal part, U-shaped.

In our cluster analysis of Pallenopsis specimens, P. tubercula n. sp., P. elephantensis n. sp. and P. gracilis are closely related (Fig. 2). P. tubercula n. sp. differs mainly from the other two species by the relative proportion between the length of the femur and tibia 2 (longer than 1), and the length of claw and auxiliar claw (lower than 1.5) (Table S2).

The dorso-distal surface of the lateral processes is a differential character between the above listed four species. P. hiemalis and P. tubercula n. sp. have the lateral processes with dorso-distal tubercle, while P. buphtalmus and P. gracilis do not have tubercles on the lateral processes. Additionally, P. tubercula n. sp. has a small bump on either side of the ocular tubercle.

In Pallenopsis hiemalis the propodus does not have heel spines (those spines being differentiated from the rest of the spines on the sole surface) (Gordon 1932GordonI.1932. Pycnogonida. Disc. Rep.6: 1-138., Pushkin 1975PushkinA.F.1975. A revision of the Pycnogonida (Pantopoda) of the Pallenopsis patagonica group in Antarctica and neighboring waters. Zool. Inst. Russ. Acad. Sci.90: 682-689., Cano-Sánchez and López-González 2019Cano-SánchezE., López-GonzálezP.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. Zootaxa4585: 517-530. 10.11646/zootaxa.4585.3.7), while in the other three species mentioned above, the propodus has longer heel spines.

The main differences among the four species compared above have been summarized in Table 2.

Pallenopsis latefrontalis Pushkin, 1993 seems to be close to P. tubercula n. sp. This species has not been included in the comparison because the original description does not provide information about the morphology of the palp or the setose pad on the movable finger of the chelifore. However, Pushkin (1993PushkinA.F.1993. The pycnogonida fauna of the South Ocean. Biological results of the Soviet Antarctic expeditions. Russ. Acad. Sci. Exp. Fauna Seas.20: 1-397.) uses the anteriorly widened cephalic segment (quadrangular aspect) on both sides of the ocular tubercle as a differential character and provides additional characters such as a dorsally concave neck, the four eyes located at the same height (see Pushkin 1993PushkinA.F.1993. The pycnogonida fauna of the South Ocean. Biological results of the Soviet Antarctic expeditions. Russ. Acad. Sci. Exp. Fauna Seas.20: 1-397.: 251, Fig. 221) and the longest article of the walking legs being tibia 2, which are differential characters between both species.

Material examined: MZB (2024-3777) holotype, one adult female, Polarstern cruise XXIII/8, stn. 605-1. S Elephant Island, 61°20.35’S 55°29.16’W, 151.3–145.8 m depth, bottom trawl, 19 December 2006. MZB (2024-3778) paratype, one adult female, Polarstern cruise XXIII/8, stn. 628-1. W Elephant Island, 61°02.28’S 55°45.61’W, 119.2–159.5 m depth, bottom trawl, 24 December 2006.

Fig. 5 Pallenopsis elephantensis n. sp. Holotype, female. A, dorsal view (showing the relative size and distribution of spinules); B, lateral view. Scale bars: 3 mm (A, B). 

Fig. 6 Pallenopsis elephantensis n. sp. Holotype, female. A, third leg, right; B, distal third leg articles; C, palm + chela of chelifore; D, palp; E, 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: 4 mm (A); 1 mm (B, E); 0.5 mm (C, D). 

Diagnosis. Proboscis slightly widened distally, up-curved. Cephalic segment not tapering anteriorly. Lateral processes separated by almost half their own diameter. Chelae fingers touching proximally when closed, movable chelae finger without setose pad. Palps longer than wide, not in contact with basal oviger process. Walking legs without long setae (long setae = subequal or longer than the diameter of the article) on the three longest articles. Second tibia longest article of the walking legs. Auxiliary claw longer than half main claw length.

Description of the holotype (female). Size moderate, leg span 154.9 mm. Proboscis mostly cylindrical, slightly up-curved, with a little widening at the end.

Trunk fully segmented, with lateral processes separated by almost half their own diameter. Segments with fine short spines mainly on the dorsal rounded elevation. Segments first, second and third ventrally bulky. Lateral processes with fine short spines mainly on dorso-distal surface. Fourth segment shorter than third segment. Cephalic segment flattened dorsally, not tapering anteriorly.

Abdomen long, down-curved, slightly widened on its distal third.

Ocular tubercle at anterior part of cephalic segment, as tall as wide and topped by a small, rounded cone. Anterior pair of eyes slightly larger than posterior pair.

Chelifores large with minute spines along entire length, increasing in density on distal surface of second scape article. First scape article shorter than second one. First scape article with a dorso-distal elevation. Second scape article wider distally. Chela palm longer than wide, with inner lateral and distal fringe of short spines. Movable finger similar in length to palm width, smooth, touching proximally when closed. Base of movable finger without spinose pad.

Palps one-articled, longer than wide. Inserted distinctly separated from oviger basal process.

Oviger nine-articled. Third article curved, fourth article is the longest oviger article and nineth article is the shortest. Three first articles smooth, fourth and fifth with small spines distally and last fourth articles spinose mainly distally.

Legs with minute spines along entire length, with increasing in density on distal articles’ surface. Second coxa shorter than sum of first and third coxae length. Second tibia longest article. Tarsus short, with ventro-distal long spines. Propodus slightly broader proximally with four long heel spines in a row, first and fourth shorter, with heterogeneous random spines along half distal sole. Main claw longer than half propodus length; auxiliary claw longer than half main claw length. Sexual pores located ventrally on second coxa of all four legs.

Measurements of holotype (mm). Length of trunk (tip of the cephalic segment to the tip of fourth lateral processes): 12.3. Width of trunk across second lateral processes: 8.5. Length of cephalic segment: 6.1. Length of proboscis: 6.0. Basal diameter of proboscis: 2.3. Greatest diameter of proboscis: 2.6. Length of abdomen: 4.5. Length of left chelifore scape: 6.4. Length of scape articles: first 3.0, second 3.4. Length of left palm: 2.4. Length of left chelae: 1.8. Length of left palp: 1.4. Length of third left leg: 73.2. Length of articles of leg 3: coxa 1 3.3, coxa 2 8.0, coxa 3 6.0, femur 1 16.2, tibia 1 12.8, tibia 2 18.0, tarsus 1.1, propodus 4.8, claw 3.0, auxiliary claws 1.6. Length of right oviger: 9.19. Length of oviger articles (first to 10th): 0.58, 1.58, 1.25, 1.66, 1.5, 1.04, 0.83, 0.42, 0.33.

Variability. The paratype specimen has a slightly broader (Trunk L/Trunk W = 1.22 vs 1.45) and shorter trunk than the holotype specimen (Trunk L/CS = 1.89 vs 2.02) (see Table S2). Moreover, the paratype specimen shows the spines on trunk and appendages slightly longer than the holotype and has shorter first heel spine of propodus.

Distribution. At present, Pallenopsis elephantensis n. sp. is known from Elephant Island, at a depth of 119.2–159.5 m.

Etymology. This species is named after the geographical area (Elephant Island) where the type specimens were collected.

Remarks. Pallenopsis elephantensis n. sp. is comparable to P. buphtalmus, P. gracilis and P. tubercula n. sp., as they share the following set of characters: (1) chelae wedge-shaped, fingers touching proximally when closed; (2) without long setae on the three longest articles of walking legs; (3) palp longer than wide; (4) neck flattened dorsally; (5) trunk with similar separation of lateral processes on proximal and distal part, U-shaped.

The absence of a clearly defined setose pad on the movable chelae finger is a differential character between P. elephantensis n. sp. and the other three related species.

The claw/auxiliar claw length ratio is considerably higher in P. buphtalmus than in P. gracilis, P. tubercula n. sp. and P. elephantensis n. sp. These last three species have been shown to be closely related in our cluster analysis (Fig. 2). Additional differential characters (see Table 2), not used in our cluster analysis, such as the number of spines on the heel, the distal shape of the neck, the shape of the abdomen and the shape of the proboscis may help differentiate P. gracilis, P. tubercula n. sp. and P. elephantensis n. sp.

The main differences among the four species compared above have been summarized in Table 2.

Material examined: See Tables 1 and 3.

Diagnosis. See Cano-Sánchez and López-González (2019Cano-SánchezE., López-GonzálezP.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. Zootaxa4585: 517-530. 10.11646/zootaxa.4585.3.7).

Remarks. P. gracilis has only been reported in its original description by Cano-Sánchez and López-González (2019Cano-SánchezE., López-GonzálezP.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. Zootaxa4585: 517-530. 10.11646/zootaxa.4585.3.7) (holotype). Therefore, the finding of this species represents the first record after its original description. The type locality of this species is Victoria Land, at a depth of 338–350 m. Our specimens were collected from Elephant Island, Joinville Island, Bransfield Strait, B-South Larsen B and Dundee Island, between 151.2 and 407.9 m depth (Table 3). Currently only 12 individuals of this species are known, including our specimens.

As discussed above, P. gracilis, P. tubercula n. sp. and P. elephantensis n. sp. seem to be closely related species (see remark section of the two new species in this paper). In fact, the characters used for the cluster analysis from the holotype and our specimens form a clearly defined group (Fig. 2). However, the set of characters: the short spine on a small latero-proximal bump on the cephalic segment, the setose pad on movable chelae finger, and the longest article of walking legs may be used to easily distinguish the three species.

The present examined specimens agree in general aspects with the description given by Cano-Sánchez and López-González (2019Cano-SánchezE., López-GonzálezP.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. Zootaxa4585: 517-530. 10.11646/zootaxa.4585.3.7) for the holotype specimen. However, we observed variability in some characters, which are shown in Table 2.

See complete list of synonyms and references in Cano-Sánchez and López-González (2019Cano-SánchezE., López-GonzálezP.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. Zootaxa4585: 517-530. 10.11646/zootaxa.4585.3.7, p. 525)

Material examined: See Tables 1 and 3.

Diagnosis. See Cano-Sánchez and López-González (2019Cano-SánchezE., López-GonzálezP.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. Zootaxa4585: 517-530. 10.11646/zootaxa.4585.3.7).

Remarks. Pallenopsis hodgsoni is considered circumpolar and has a wide depth range, 120–2450 m (Child 1995ChildC.A.1995. Antarctic and Subantarctic Pycnogonida V. The Families Pycnogonidae, Phoxichiliidae, Endeididae and Callipallenidae, including the genus Pallenopsis. Antarc. Res. Ser.69: 113-160. 10.1029/AR069p0113). Our specimens do not modify the known information about the geographical and bathymetric distribution of this species.

Pallenopsis hodgsoni has been considered a synonym of P. pilosa by some authors (Turpaeva 1974TurpaevaE.P.1974. The pycnogonida of the Scotia Sea and surrounding waters. Tr. Inst. Okeanol., Akad. Nauk. SSSR98: 277-305., Pushkin 1993PushkinA.F.1993. The pycnogonida fauna of the South Ocean. Biological results of the Soviet Antarctic expeditions. Russ. Acad. Sci. Exp. Fauna Seas.20: 1-397., Munilla and Soler-Membrives 2009MunillaT., Soler-MembrivesA.2009. Check-list of the pycnogonids from Antarctic and sub-Antarctic waters: zoogeographic implications. Antarctic Sci.21: 99-111. 10.1017/S095410200800151X). However, other authors recognize both species as valid (Child 1995ChildC.A.1995. Antarctic and Subantarctic Pycnogonida V. The Families Pycnogonidae, Phoxichiliidae, Endeididae and Callipallenidae, including the genus Pallenopsis. Antarc. Res. Ser.69: 113-160. 10.1029/AR069p0113, Munilla and Soler-Membrives 2015MunillaT., Soler-MembrivesA.2015. Pycnogonida from the Bellingshausen and Amundsen seas: taxonomy and biodiversity. Polar Biol.38: 413-430. 10.1007/s00300-014-1585-8, Cano-Sánchez and López-González 2019Cano-SánchezE., López-GonzálezP.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. Zootaxa4585: 517-530. 10.11646/zootaxa.4585.3.7).

Cano-Sánchez and López-González (2019Cano-SánchezE., López-GonzálezP.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. Zootaxa4585: 517-530. 10.11646/zootaxa.4585.3.7) summarized the information provided by earlier authors on the differential characters between the two species, and then these authors proposed a set of diagnostic characters for P. hodgsoni. The specimens examined here agree in general aspects with this description, only one specimen (P. 1072) has auxiliary claws longer than half main claw length.

In our cluster analysis, the examined P. hodgsoni specimens form a well-defined group (Fig. 2). However, this group is heterogeneous and within it we can observe defined subgroups, all of them attributed here to P. hodgsoni (Fig. 2), since we have not observed additional differential characters. Further integrative taxonomic studies on this species are needed, exploring whether the molecular results are consistent with the subgroups obtained from the analysis of large data sets of morphological characters, allowing or not the consideration of different species now under the name of P. hodgsoni.

Pallenopsis macronyx Bouvier, 1911BouvierE.L.1911. Les Pycnogonides des Pourquoi Pas?C. R. Hebd. Seances Acad. Sci.152: 1136-1142., p. 1139; 1913, pp. 112-117 (Figs. 66–73); Child, 1995ChildC.A.1995. Antarctic and Subantarctic Pycnogonida V. The Families Pycnogonidae, Phoxichiliidae, Endeididae and Callipallenidae, including the genus Pallenopsis. Antarc. Res. Ser.69: 113-160. 10.1029/AR069p0113, p. 145; Munilla and Soler-Membrives, 2009MunillaT., Soler-MembrivesA.2009. Check-list of the pycnogonids from Antarctic and sub-Antarctic waters: zoogeographic implications. Antarctic Sci.21: 99-111. 10.1017/S095410200800151X (list.); 2015MunillaT., Soler-MembrivesA.2015. Pycnogonida from the Bellingshausen and Amundsen seas: taxonomy and biodiversity. Polar Biol.38: 413-430. 10.1007/s00300-014-1585-8 (list.); Bamber et al., 2023BamberR.N., El NagarA., ArangoC.P. (eds) 2023. Pycnobase: World Pycnogonida Database. Accessed at https://www.marinespecies.org/pycnobase on 2023-06-22. doi:10.14284/360 (list.)

Pallenopsis knipovichi Turpaeva, 1974TurpaevaE.P.1974. The pycnogonida of the Scotia Sea and surrounding waters. Tr. Inst. Okeanol., Akad. Nauk. SSSR98: 277-305., pp. 291–293 (Fig. 7); Munilla, 1991MunillaT.1991. Picnogónidos capturados en la campaña “Antártida 8811”. Bol. Inst. Esp. Oceanogr.7: 3-44., pp. 32–34 (Fig. 15)

Bathypallenopsis macronyx Pushkin, 1993PushkinA.F.1993. The pycnogonida fauna of the South Ocean. Biological results of the Soviet Antarctic expeditions. Russ. Acad. Sci. Exp. Fauna Seas.20: 1-397., p. 271

Material examined: See Tables 1 and 3.

Diagnosis. Lateral processes separated by less than half their own diameter. Chelae fingers curved, slender and leaving a gap proximally when closed, without setose pad. Palps longer than wide. Walking legs without long setae (subequal or longer than the diameter of the article) on the three longest articles. Femur subequal or longer than tibia 1. Propodus narrowing distally. Claw longer than propodus. No auxiliary claw.

Remarks. Pallenopsis macronyx has a wide geographical distribution in Antarctic and sub-Antarctic waters. It has been cited in the Scotia Sea, Antarctic Peninsula, Ross Sea and Weddell Sea, over a wide depth range, 100–1138 m (Munilla and Soler-Membrives 2009MunillaT., Soler-MembrivesA.2009. Check-list of the pycnogonids from Antarctic and sub-Antarctic waters: zoogeographic implications. Antarctic Sci.21: 99-111. 10.1017/S095410200800151X). Our specimens are within the known geographic and bathymetric range for this species.

The P. macronyx specimens examined here agree with diagnoses provided by Bouvier (1913BouvierEL. 1913. Pycnogonides du pourquoi Pas? In: CalmanW.T. (ed), Deuxième Expédition Antarctique française (1908-1910), 6. Masson, Paris, pp. 1-169. 10.5962/bhl.title.10303), Turpaeva (1974TurpaevaE.P.1974. The pycnogonida of the Scotia Sea and surrounding waters. Tr. Inst. Okeanol., Akad. Nauk. SSSR98: 277-305.), Pushkin (1993PushkinA.F.1993. The pycnogonida fauna of the South Ocean. Biological results of the Soviet Antarctic expeditions. Russ. Acad. Sci. Exp. Fauna Seas.20: 1-397.) and Child (1995ChildC.A.1995. Antarctic and Subantarctic Pycnogonida V. The Families Pycnogonidae, Phoxichiliidae, Endeididae and Callipallenidae, including the genus Pallenopsis. Antarc. Res. Ser.69: 113-160. 10.1029/AR069p0113). This species shows conspicuous features such as chelae fingers curved, slender and leaving a gap proximally when closed; propodus narrowing distally; claw longer than propodus; without auxiliary claw. In fact, our P. macronyx material forms a clearly defined group in the cluster analysis (see Fig. 2).

Pallenopsis spicata Hodgson, 1914HodgsonT.V.1914. Preliminary report of the Pycnogonida of the German Southpolar Expedition 1901-1903. Zool. Anz.45: 158-165.–15HodgsonT.V.1915. The Pycnogonida collected by the Gauss in the Antarctic regions, 1901-1903.- Preliminary report. Ann. Mag. Nat. Hist. (ser 8) 15: 141-149. 10.1080/00222931508693621, p. 146; 1927HodgsonT.V.1927. Die Pycnogoniden der Deutschen Südpolar-Expedition 1901-1903. Deut. Sudp. Exp. Ser. II Zool.19: 303-358., pp. 338–339 (Fig. 10); Calman, 1915CalmanW.T.1915. Pycnogonida. British Antarctic (Terra Nova) Expedition, 1910. Zoology3: 1-74., pp. 44–46 (Fig. 9); Gordon, 1932GordonI.1932. Pycnogonida. Disc. Rep.6: 1-138., pp. 90–91; 1938GordonI.1938. Pycnogonida. Sci. Rep. Australas. Antarc. Exp. Zool. Bot.2: 1-40., p. 19; 1944, p. 48; Arnaud, 1972ArnaudF.1972. Pycnogonides. Invertébrés Marins. XIIeme et XVeme Expeditions Antarctiques Françaises en Terre Adélie. Tethys4: 135-156., p. 148; Krapp, 1980KrappF.1980. Neue Pantopodenfunde (Pycnogonida, Arthropoda) nahe der Belgischen Antarktis-Station. Bull. Inst. R. Sci. Nat. Belg.52: 1-8., p. 6; Munilla and Soler-Membrives, 2009MunillaT., Soler-MembrivesA.2009. Check-list of the pycnogonids from Antarctic and sub-Antarctic waters: zoogeographic implications. Antarctic Sci.21: 99-111. 10.1017/S095410200800151X (list.); Bamber et al., 2023BamberR.N., El NagarA., ArangoC.P. (eds) 2023. Pycnobase: World Pycnogonida Database. Accessed at https://www.marinespecies.org/pycnobase on 2023-06-22. doi:10.14284/360 (list.)

Clavigeropallene spicata. Pushkin, 1974PushkinA.F.1974. Clavigeropallene gen. n. (Pantopoda) from Antarctic. Zool. Inst. Russ. Acad. Sci.99: 938-940., pp. 938–940 (Fig. 1); 1993PushkinA.F.1993. The pycnogonida fauna of the South Ocean. Biological results of the Soviet Antarctic expeditions. Russ. Acad. Sci. Exp. Fauna Seas.20: 1-397., pp. 210–212 (Fig. 190)

Material examined: See Tables 1 and 3.

Diagnosis. Three anterior trunk segments with a pair of dorsal conical tubercles. Lateral processed with dorso-distal conical tubercle. Cephalic segment wider than long and swollen over the base of each chelifore. Chelifore with scape undivided, chelae fingers touching proximally when closed, movable chelae finger considerably larger than immovable finger and swollen on the outer surface. Walking legs without long setae (subequal or longer than the diameter of the article) on three longest articles. First coxae of walking legs with dorso-distal conical tubercle. Second tibia longest article of walking legs. No auxiliary claw.

Remarks. Pallenopsis spicata is considered circumpolar with a wide depth range, 25–549 m (Child 1995ChildC.A.1995. Antarctic and Subantarctic Pycnogonida V. The Families Pycnogonidae, Phoxichiliidae, Endeididae and Callipallenidae, including the genus Pallenopsis. Antarc. Res. Ser.69: 113-160. 10.1029/AR069p0113, Munilla and Soler-Membrives 2009MunillaT., Soler-MembrivesA.2009. Check-list of the pycnogonids from Antarctic and sub-Antarctic waters: zoogeographic implications. Antarctic Sci.21: 99-111. 10.1017/S095410200800151X). Our specimens do not modify the known information about the geographical and bathymetric distribution of this species.

The specimens of P. spicata examined in this study agree with the description provided by previous authors (Hodgson 1927HodgsonT.V.1927. Die Pycnogoniden der Deutschen Südpolar-Expedition 1901-1903. Deut. Sudp. Exp. Ser. II Zool.19: 303-358., Krapp 1980KrappF.1980. Neue Pantopodenfunde (Pycnogonida, Arthropoda) nahe der Belgischen Antarktis-Station. Bull. Inst. R. Sci. Nat. Belg.52: 1-8., Child 1995ChildC.A.1995. Antarctic and Subantarctic Pycnogonida V. The Families Pycnogonidae, Phoxichiliidae, Endeididae and Callipallenidae, including the genus Pallenopsis. Antarc. Res. Ser.69: 113-160. 10.1029/AR069p0113). This species exhibits a particular set of characters that ensure that it cannot be confused with any other Antarctic or sub-Antarctic Pallenopsis species, these features being trunk, lateral processed and first coxae with dorsal conical tubercles; cephalic segment swollen over the base of chelifores; scape undivided; and no auxiliary claw.

Material examined: See Tables 1 and 3.

Remarks. Pallenopsis aff. vanhoeffeni is morphologically very close to P. vanhoeffeni. Our specimens were collected from South Shetland Islands, Joinville Island, Bransfield Strait, B-South Larsen B and Dundee Island, between 259.2 and 361.2 m depth (Table 3).

P. vanhoeffeni is another setose species close to P. hodgsoni and P. pilosa, with broad, wedge-shaped chelae fingers, touching when closed and without a setose pad on the movable finger. Our P. aff. vanhoeffeni material forms a clearly defined group in the cluster analysis (see Fig. 2). However, characters such as the presence of long setae on the three long articles of legs arranged in rows, on dorsal and lateral surfaces, and the small antero-lateral bump on the cephalic segment may be used to easily distinguish P. vanhoeffeni and P. aff. vanhoeffeni from the other setose species above listed.

The specimens examined for this study agree in general aspects with the description of P. vanhoeffeni provided by previous authors (Hodgson 1927HodgsonT.V.1927. Die Pycnogoniden der Deutschen Südpolar-Expedition 1901-1903. Deut. Sudp. Exp. Ser. II Zool.19: 303-358., Child 1995ChildC.A.1995. Antarctic and Subantarctic Pycnogonida V. The Families Pycnogonidae, Phoxichiliidae, Endeididae and Callipallenidae, including the genus Pallenopsis. Antarc. Res. Ser.69: 113-160. 10.1029/AR069p0113, Cano-Sánchez and López-González 2019Cano-SánchezE., López-GonzálezP.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. Zootaxa4585: 517-530. 10.11646/zootaxa.4585.3.7). However, most of the specimens examined here did not show some features, such as the two dorsal groups of long, slender setae on the three anterior segments (specimens MZB 2024-3805 to MZB 2024-3808) BECA P.1070; P. 1073; P.1076; P.1096; P.1120), or auxiliary claws shorter than half the claw length (specimens MZB 2024-3804 to MZB 2024-3806, and MZB 2024-3808) BECA P.1071; P.1096; P.1120; P.1122) (see also Table S2), as previously reported. For these reasons, we preferred to not include at this time a diagnosis for this material, and maintain our specimens as a form close to Hodgson’s species. We consider it too risky, from a nomenclatural point of view, to include this variability in the current conception of P. vanhoeffeni, or to propose the description of a new species, or to consider it as a species complex. Therefore, we leave the final identification of this material pending examination of additional specimens and, where possible, other sources of information.

Key to Antarctic and sub-Antarctic species of Pallenopsis (adults)

The key proposed here is an update of the key to Antarctic and sub-Antarctic species of Pallenopsis (adults) published by Cano-Sánchez and López-González (2019Cano-SánchezE., López-GonzálezP.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. Zootaxa4585: 517-530. 10.11646/zootaxa.4585.3.7). It includes the newly described species and considers the new knowledge concerning the variability of some characters.

1. Chelae fingers curved, slender and leaving a gap proximally when closed 2

1’. Chelae fingers broad, wedge-shaped and touching proximally when closed (fingers touching along their entire length or having a gap between them at mid-length) 6

2. Without or with small auxiliary claw (less than one-third of the main claw) 3

2’. With auxiliary claw (more than one-third of the main claw 4

3. Claw longer than propodus. Without auxiliary claw P. macronyx Bouvier, 1911BouvierE.L.1911. Les Pycnogonides des Pourquoi Pas?C. R. Hebd. Seances Acad. Sci.152: 1136-1142.

3’. Claw subequal or shorter than propodus. With small auxiliary claws

P. longiseta Turpaeva, 1957

4. Dorsal series of long forward curved setae on the three longer articles of the walking legs

P. meridionalis Hodgson, 1914HodgsonT.V.1914. Preliminary report of the Pycnogonida of the German Southpolar Expedition 1901-1903. Zool. Anz.45: 158-165.⁽¹⁾

4’. Without these dorsal series of curved setae 5

5. Lateral processes about 1.5 times longer than their diameter. Chelae immovable finger placed perpendicularly at half length of lateral edge palm P. lateralia Child, 1995ChildC.A.1995. Antarctic and Subantarctic Pycnogonida V. The Families Pycnogonidae, Phoxichiliidae, Endeididae and Callipallenidae, including the genus Pallenopsis. Antarc. Res. Ser.69: 113-160. 10.1029/AR069p0113

5’. Lateral processes as long as wide. Chelae fingers (movable and immovable) placed distally on palm

P. villosa Hodgson, 1907HodgsonT.V.1907. Pycnogonida. National Antarctic Expedition 1901-1904. Reports of the National Antarctic expedition of 1901-1904. Nat. Hist.3: 1-172.

6. Without auxiliary claw P. spicata Hodgson, 1915HodgsonT.V.1915. The Pycnogonida collected by the Gauss in the Antarctic regions, 1901-1903.- Preliminary report. Ann. Mag. Nat. Hist. (ser 8) 15: 141-149. 10.1080/00222931508693621

6’. With auxiliary claw 7

7. Propodus with 5 small, short heel spines P. lattina Pushkin, 1993PushkinA.F.1993. The pycnogonida fauna of the South Ocean. Biological results of the Soviet Antarctic expeditions. Russ. Acad. Sci. Exp. Fauna Seas.20: 1-397.⁽¹⁾

7’. Propodus with other configuration 8

8. Proboscis with distinct swelling in the middle P. yepayekae Weis, 2014WeisA., MeyerR., DietzL., et al.2014. Pallenopsis patagonica (Hoek, 1881) - a species complex revealed by morphology and DNA barcoding, with description of a new species of Pallenopsis Wilson, 1881. Zool. J. Linn. Soc.170: 110-131. 10.1111/zoj12097

8’. Proboscis without swelling in the middle 9

9. Setae on the three longest articles of walking legs mostly long (subequal or longer than the diameter of the article) 10

9’. Setae on the three longest articles of walking legs mostly short 13

10. Movable finger of chelae with setose pad P. rotunda Cano-Sánchez and López-González, 2019Cano-SánchezE., López-GonzálezP.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. Zootaxa4585: 517-530. 10.11646/zootaxa.4585.3.7

10’. Movable finger of chelae without setose pad 11

11. Long setae without setules P. pilosa (Hoek, 1881)

11’. Long setae with setules 12

12. Walking legs with setae less than two times longer than the diameter of the article

P. vanhoeffeni Hodgson, 1915HodgsonT.V.1915. The Pycnogonida collected by the Gauss in the Antarctic regions, 1901-1903.- Preliminary report. Ann. Mag. Nat. Hist. (ser 8) 15: 141-149. 10.1080/00222931508693621

12’. Walking legs with setae more than two times longer than the diameter of the article

P. hodgsoni Gordon, 1938GordonI.1938. Pycnogonida. Sci. Rep. Australas. Antarc. Exp. Zool. Bot.2: 1-40.

13. All lateral processes touching proximallyP. obliqua (Thomson, 1884)

13’. Not all lateral processes touching proximally 14

14. Proboscis tip truncated (flat mouth) P. boehmi Schmkewitsch, 1930 ⁽¹⁾

14’. Proboscis tip rounded 15

15. Movable and immovable chelae fingers well curved, on entire inner and external edges

P. candidoi Mello-Leitao, 1949

15’. Movable and immovable chelae fingers only slightly curved on external edges, but inner edges straight at least half their length 16

16. Ratio claw/auxiliar claw length >3 P. buphtalmus Pushkin, 1993PushkinA.F.1993. The pycnogonida fauna of the South Ocean. Biological results of the Soviet Antarctic expeditions. Russ. Acad. Sci. Exp. Fauna Seas.20: 1-397.

16’. Ratio claw/auxiliar claw length <3 17

17. Crossed fingertips of the chela when closed P. kupei Clark, 1971

17’. Parallel fingertips of chelae when closed 18

18. Femur is the longest article of the walking legs P. tubercula n. sp.

18’. Tibia 2 is the longest article of the walking legs 19

19. Cephalic segment widened anteriorly (quadrangular) on either side of the ocular tubercle P. latefrontalis Pushkin, 1993PushkinA.F.1993. The pycnogonida fauna of the South Ocean. Biological results of the Soviet Antarctic expeditions. Russ. Acad. Sci. Exp. Fauna Seas.20: 1-397.

19’. Cephalic segment not widened anteriorly (not quadrangular) on either side of the ocular tubercle20

20. Ratio length/width of palp > 1.5 21

20’. Ratio length/width of palp <1.5 25

21. Lateral processes with a dorso-distal tubercle 22

21’. Lateral processes without a dorso-distal tubercle 24

22. Propodus without distinct heel spines P. hiemalis Hodgson, 1907HodgsonT.V.1907. Pycnogonida. National Antarctic Expedition 1901-1904. Reports of the National Antarctic expedition of 1901-1904. Nat. Hist.3: 1-172.⁽¹⁾

22’. Propodus with distinct heel spines 23

23. Chelae with setose pad attached along its entire length to the base of the movable finger

P. aulaeturcarum Dömel and Melzer, 2019DömelJ.S., MacherT., DietzL., et al.2019. Combining morphological and genomic evidence to resolve species diversity and study speciation processes of the Pallenopsis patagonica (Pycnogonida) species complex. Front Zool16: 36. 10.1186/s12983-019-0316-y

23’. Chelae with setose pad attached only by its basal half to the base of the movable finger

P. obstaculumsuperavit Dömel and Melzer, 2019DömelJ.S., MacherT., DietzL., et al.2019. Combining morphological and genomic evidence to resolve species diversity and study speciation processes of the Pallenopsis patagonica (Pycnogonida) species complex. Front Zool16: 36. 10.1186/s12983-019-0316-y

24. Movable finger of chelae with setose pad P. gracilis Cano-Sánchez and López-González, 2019Cano-SánchezE., López-GonzálezP.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. Zootaxa4585: 517-530. 10.11646/zootaxa.4585.3.7

24’. Movable finger of chelae without setose pad P. elephantensis n. sp.

25. Ratio length/width of propodus >>4 P. tumidula Loman, 1923⁽²⁾

25’. Ratio length/width of propodus <4 26

26. Proboscis without any widening along the entire length P. patagonica (Hoek, 1881)⁽¹⁾

26’. Proboscis with some widening at its length 27

27. Propodus with long spines on more than half of sole P. gurjanovi Pushkin, 1993PushkinA.F.1993. The pycnogonida fauna of the South Ocean. Biological results of the Soviet Antarctic expeditions. Russ. Acad. Sci. Exp. Fauna Seas.20: 1-397.

27’. Propodus with heel spines (on not more than half of sole) P. leiopus Pushkin, 1993PushkinA.F.1993. The pycnogonida fauna of the South Ocean. Biological results of the Soviet Antarctic expeditions. Russ. Acad. Sci. Exp. Fauna Seas.20: 1-397.

(1) We consider these species following the same criteria as Cano-Sánchez and López-González (2019Cano-SánchezE., López-GonzálezP.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. Zootaxa4585: 517-530. 10.11646/zootaxa.4585.3.7).

(2) The original description of P. tumidula notes in text that “Palp a thick, round knob between bases of chelifore and oviger” but the illustration does not show the palp clearly. Moreover, this description did not provide information about the chelae fingers or propodus morphology, but Stock (1957StockJ.H.1957. Pantopoden aus dem Zoologischen Museum Hamburg. Mitt. Hamb. Zool. Museum Inst.55: 91-106.) illustrated the syntypes of this species showing the chelae and propopdus morphology.