Pseudolitochira spinosa, Ng, 2024

Ng, Peter K. L., 2024, Pseudolitochira spinosa, a new species of pilumnid crab from Panglao, Philippines, with a note on P. setosa (A. Milne-Edwards, 1873) (Crustacea, Brachyura, Pilumnoidea), Zootaxa 5512 (1), pp. 120-126 : 121-125

Pseudolitochira spinosa sp. nov.

( Figs. 1–3 )

Material examined. Holotype: female (4.9 × 3.1 mm) (NMCR, ex ZRC 2021.0273 ), station B18, under blocks dispersed among seagrass bed, Sungcolan Bay , Panglao, Bohol, Philippines, 09º38.5’N 123º49.7’E, 3-5 m, coll. PANGLAO 2004 Expedition, 20 June 2004.

Diagnosis. Carapace transversely ovate, width 1.6 times length ( Fig. 2A, B ); surface smooth, regions poorly indicated, covered with scattered pubescence, frontal and anterolateral margins with denser, long silk-like pubescence, those lining postfrontal ridge relatively shorter ( Figs. 1 , 2A–C ); frontal margin wide, with 2 low truncate lobes, separated by shallow median notch ( Fig. 2A, B ); supraorbital margin sinuous, with median low notch ( Fig. 2B ); external orbital tooth low, separated from first anterolateral spine by broad concavity, second anterolateral spine prominent, last anterolateral tooth small, visible as low tubercle ( Fig. 2B ). Posterior margin of epistome with median lobe broadly triangular, produced with median fissure, lateral margin concave, entire ( Fig. 2D ). Third maxilliped with short, subquadrate ischium; merus quadrate, anteroexternal angle rounded, not auriculiform, subdistal margin with low granules (Fig. 6D). Chelipeds homochelous; inner margin of merus with 2 distinct spines; inner angle of carpus with strong sharp triangular tooth; chela with fingers subequal to length of palm, outer surface covered with granules and long setae partially obscuring margins ( Figs. 2A , 3C–E ). Ambulatory legs with merus and propodus relatively short, stout; all meri unarmed; lined with dense long silk-like setae ( Figs. 2A , 3B ). Vulvae large, ovate, opening obliquely, positioned close to median part of sternite 6 ( Fig. 3F ).

Colour in life. Overall red on dorsal surfaces with chelae paler in colour ( Fig. 1 ).

Etymology. The species is named “ spinosa ” for its prominent anterolateral spines.

Remarks. The wide carapace of P. spinosa sp. nov. (width to length ratio 1.6) allies it with P. maenosonoi from Okinawa in Japan (width to length ratio 1.52–1.74) but can be separated from that species by its anterolateral margin possessing two sharp, well developed spines after the low external orbital tooth ( Fig. 2A, B ) (versus anterolateral margin with two low lobes in P. maenosonoi ; Ng & Clark 2022: fig. 3a, b); the merus of the third maxilliped is slightly more elongate and the ischium longer ( Fig. 3A ) (versus merus quadrate and ischum short in P. maenosonoi ; Ng & Clark 2022: figs. 3e, 7a); the inner angle of the carpus of the cheliped has a sharp triangular tooth ( Figs. 2A , 3C ) (versus inner angle truncate and low in P. maenosonoi ; Ng & Clark 2022: fig. 1a, b); the inner margin of the merus of the cheliped has two sharp spines ( Fig. 3C, E ) (versus with several low sharp granules in P. maenosonoi ; Ng & Clark 2022: fig. 3f); and the fourth ambulatory merus is relatively longer ( Fig. 3B ) (versus shorter and stouter in P. maenosonoi ; Ng & Clark 2022: fig. 4e, f).

The carapaces of P. integra , P. setosa , P. pacifica , P. crinita , P. taiwang and P. lanuginosa are proportionately more quadrate than that of P. spinosa sp. nov., the width to length ratio being less than 1.5 ( Fig. 4E–H ; Ng et al. 2021: figs. 3A, 4A, 5A; Ng & Clark 2022: fig. 5a, e; Ng & Clark 2022: fig. 1A, B; Ng & Lin 2023: figs. 6A, 7A). Compared to P. integra , P. spinosa sp. nov. can be distinguished in having the lobes of the frontal margin truncate with gently convex margins ( Fig. 2A, B ) (versus margins rounded and slightly more projecting in P. integra ; Ng et al. 2021: figs. 4A, 5A); the anterolateral margin is short and armed with distinct spines ( Fig. 2A, B ) (versus margin arcuate with low lobes, margin appearing almost entire in P. integra ; Ng et al. 2021: figs. 3A, 4A, 5A); the ischium of the third maxilliped is relatively more rectangular in shape ( Fig. 3A ) (versus more quadrate in P. integra ; Ng et al. 2021: fig. 5D); the inner angle of the carpus of the cheliped has a prominent sharp tooth ( Fig. 3C ) (versus angle rounded and low in P. integra ; Ng et al. 2021: figs. 3A, 4A, B,); and the inner margin of the merus of the cheliped is armed with two spines ( Fig. 3C ) (versus smooth or with low granules in P. integra ; Ng et al. 2021: fig. 5B).

The poorly known P. setosa s. str. (type locality New Caledonia) is also figured here ( Fig. 4 ). Ng & Lin (2023) transferred the species to Pseudolitochira after examining the types in MNHN, briefly noting that it has the distinctive posterior margin of the epistome diagnostic of the genus ( Fig. 4B, C ). The syntype series of P. setosa consists of four specimens, two males and two females, all dried and pasted on a card in one box under the catalogue number MNHN B3057 ( Fig. 4B ). Alphonse Milne-Edwards (1873: 267–268, pl. 12 fig. 2) stated he had several specimens with him and gave a size of 9.0 × 6.0 mm (sex not indicated), although he figured a smaller male in his plate (reproduced here in Fig. 4A, B ). It is difficult to match his measured specimen and figured male with one of the four specimens on hand. The specimens are all extremely delicate, glued firmly on the card, and it was not possible to clean them very much, make more detailed dissections or study without damaging them. In the interest of stability, the best-preserved male, 7.4 × 5.1 mm (MNHN B3057a), is selected here as the lectotype of Carcinoplax setosus A. Milne-Edwards, 1873 . Compared to P. setosa , P. spinosa sp. nov. can be separated by its anterolateral margin possessing two sharp, well developed spines after the low external orbital tooth ( Fig. 2A, B ) (versus anterolateral margin with two low dentiform lobes in P. setosa ; Fig. 4A, E–H ); the median triangular part of the posterior margin of the epistome has a distinct longitudinal fissure ( Fig. 2D ) (versus with only a small notch in P. setosus ; Fig. 4C ); and the inner margin of the merus of the cheliped has two sharp spines ( Fig. 3C, E ) (versus with several low sharp granules in P. setosus ; Fig. 4F ).

The carapace of P. crinita is distinctly more ovate in shape, with the anterolateral margin more convex and the overall surfaces strongly setose (Ng & Clark 2022: fig. 5e). The median lobe of the posterior margin of the epistome in P. spinosa sp. nov. is produced ( Fig. 2D ) but in P. pacifica and P. crinita , the median part is more depressed and almost level with the endostome (Ng & Clark 2022: fig. 5b, c, f, g). The merus of the third maxilliped of P. spinosa sp. nov. is also slightly more elongate and the ischium is longer ( Fig. 3A ) compared to P. pacifica which has the merus quadrate and the ischum short (Ng & Clark 2022: figs. 5d, 7b).

Pseudolitochira spinosa sp. nov. further differs from P. lanuginosa in that the merus and ischium of the third maxilliped are distinctly longer, with the anteroexternal angle of the merus not auriculiform ( Fig. 3A ) (versus shorter and more quadrate, with the anteroexternal angle of the merus auriculiform in P. lanuginosa ; Ng & Clark 2022: fig. 2D); and the ambulatory meri are relatively longer ( Figs. 2A , 3B ) (versus distinctly shorter and stouter in P. lanuginosa ; Ng & Clark 2022: figs. 1A, B, 2G). Compared to P. taiwang , P. spinosa sp. nov. is easily distinguished by the overall surface being setose but not dense enough to obscure surfaces and margins ( Fig. 1 ) (versus more densely setose with margins obscured; Ng & Lin 2023: figs. 1D, 6A, 7A); the dorsal surface of the carapace less convex in frontal view ( Fig. 2C ) (versus carapace distinctly higher; Ng & Lin 2023: fig. 6C); the median lobe of the posterior margin of the epistome has a distinct longitudinal fissure ( Fig. 2D ) (versus without a fissure; Ng & Lin 2023: fig. 6E); the carpus of the cheliped has a long tooth on the inner angle ( Figs. 2A , 3C ) (versus low and truncate; Ng & Lin 2023: figs. 6A, 7A); and the ambulatory meri are distinctly longer ( Figs. 2A , 3B ) (versus short and stout; Ng & Lin 2023: figs. 6A, H, 7).

Figures

FIGURE 1. Pseudolitochira spinosa sp. nov., holotype female (4.9 × 3.1 mm) (NMCR), Philippines. Colour in life.

FIGURE 2. Pseudolitochira spinosa sp. nov., holotype female (4.9 × 3.1 mm) (NMCR), Philippines. A, overall dorsal view; B, right anterolateral margin and orbit; C, frontal view of cephalothorax; D, epistome.

FIGURE 3. Pseudolitochira spinosa sp. nov., holotype female (4.9 × 3.1 mm) (NMCR), Philippines. A, left third maxilliped; B, right fourth ambulatory leg; C, dorsal view of right cheliped; D, outer view of chelae; E, buccal cavity, thoracic sternum and pleon; F, sternopleonal cavity and vulvae.

FIGURE 4. Pseudolitochira setosa (A. Milne-Edwards, 1873).A, E–H, overall dorsal habitus; B, frontal view of cephalothorax; C, posterior margin of epistome (left side damaged); D, four syntypes in box in MNHN B3057. A, B, male, after A. Milne- Edwards (1873: pl. 12 fig. 2, 2a); C, E, paralectotype female (7.3 × 5.0 mm) (MNHN B3057b); F, paralectotype female (crushed, carapace width 8.5 mm) (MNHN B3057b); G, paralectotype male (6.6 × 4.6 mm) (MNHN B3057b); H, lectotype male (7.4 × 5.1 mm) (MNHN B3057a).