Scyramathia tenuipes, Lee & Richer De Forges & Ng, 2020

Lee, Bee Yan, Richer De Forges, Bertrand & Ng, Peter K. L., 2020, Revision of the deep-water spider crab genus, Scyramathia A. Milne-Edwards, 1880, with the description of a new species from the Mediterranean and notes on Rochinia A. Milne-Edwards, 1875, and Anamathia Smith, 1885 (Crustacea, Decapoda, Brachyura, Epialtidae), Zoosystematics and Evolution 96 (2), pp. 537-569 : 537

Scyramathia tenuipes sp. nov. Figs 12 , 13A-C , 14F-J , 15E-H

Scyramathia Carpenteri : A. Milne-Edwards and Bouvier 1894: 13, 14 (in part); A. Milne-Edwards and Bouvier 1899: 43 (in part), pl. 1 fig. 4; Bouvier 1922: 81 (in part). [not Amathia carpenteri Norman, in Thomson 1873].

Rochinia Carpenteri : Bouvier 1940: 344, 345 (in part), fig. 209, pl. 14 figs 1-3. [not Amathia carpenteri Norman, in Thomson 1873].

Rochinia (Amathia) carpenteri : Dieuzeide 1955: 53-55, fig. 9.

Rochinia (Scyramathia) carpenteri : Dieuzeide and Roland 1958: 21 (list), 62 (list). [not Amathia carpenteri Norman, in Thomson 1873].

Rochinia carpenteri : Dieuzeide 1960: 76 (list); Fransen 1991: 6, (list), 7 (list), 181 (list); García Raso 1996: 741 (in part); D’Udekem d’Acoz 1999: 194 (in part); Abelló et al. 2002: 187 (table), 189 (list), 191 (table), 193 (table), 195 (table); Araújo et al. 2014: 38, fig. 1F. [not Amathia carpenteri Norman, in Thomson 1873].

Material examined.

Holotype: ♂ (33.9 × 26.3 mm) (ICMD288), Mediterranean Sea, coll. 1994. Paratypes: 1 ovigerous ♀ (31.2 × 24.6 mm) (ICMD000708), Málaga, Mediterranean Sea, 36°31'19"N, 03°59'18"W, 650 m, coll. 1 May 2016; 1 ♀ (27.7 × 20.5 mm) (ICMD000712), Castell de Ferro, Mediterranean Sea, 36°39'19"N, 03°16'47"W, 638 m, coll. 5 May 2016; 1 ovigerous ♀ (32.2 × 25.8 mm) (ZRC 2019.1635, ex. ICMD000696), Adra, Mediterranean Sea, 36°33'51"N, 03°03'52"W, 572 m, coll 29 April 2016; 1 ♂ (32.0 × 25.4 mm) (ZRC 2019.1636, ex. ICMD000713), Málaga, Mediterranean Sea, 36°18'44"N, 04°20'25"W, 770 m, coll. 24 April 2016; 1 ♂ (29.6 × 22.9 mm) (ICMD000700), Alborán Island, Mediterranean Sea, 35°33'51"N, 03°03'52"W, 819 m, coll. 6 May 2016; 1 ♂ (29.7 × 22.0 mm) (ICMD000707), Málaga, Mediterranean Sea, 35°31'7"N, 03°59'18"W, 650 m, coll. 1 May 2016; 1 ovigerous ♀ (30.6 × 23.7 mm) (ICMB000711), Castell de Ferro, Mediterranean Sea, 36°39'19"N, 03°16'47"W, 638 m, coll. 5 May 2016; 1 ♂ (14.9 × 10.5 mm) (ZRC 2019.1637, ex. ICMD000706), Málaga, Mediterranean Sea, 36°31'19"N, 03°59'18"W, 650 m, coll. 1 May 2016; 1 ♀ (16.3 × 12.5 mm) (ZRC 2019.1638, ex. ICMB000705), Málaga, Mediterranean Sea, 36°31'19"N, 03°59'18"W, 650 m, coll. 1 May 2016.

Diagnosis.

Carapace pyriform. Pseudorostral spines straight, almost half of carapace length. Supraorbital eave fused with carapace, with blunt preorbital spine; postorbital lobe fused with hepatic spine. Carapace with plates: 1 hepatic spine, 1 small granule above 1 oblong mesogastric plate, 1 protogastric granule, 1 epibranchial plate, 1 oblong cardiac plate, 1 metabranchial granule, 1 lateral branchial spine, 1 blunt posterior spine (Figs 12 , 13A ). Antennal flagellum shorter than pseudorostral spines, about half of pseudorostral length. Basal antennal article longer than broad, straight outer margin with blunt roundish distal angle of article (Fig. 13B ). Buccal frame with distal angle of buccal frame slightly raised with round edge. Pterygostomial region with 3 or 4 granules on outer margins (Fig. 13B ). Chelipeds slender, propodus longer than fingers, slightly carinate margin; carpus with granules; merus smooth, triangular in cross-section. Ambulatory legs slender; merus with distal angle blunt; male P2 merus length 1.0-1.4 times carapace length, female P2 merus length 1.0-1.3 times carapace length, male P2 merus length 17.3-20.5 times width, female P2 merus length 14.8-21.5 times width; male P5 merus length 0.4-0.7 times carapace length, female P5 merus length 0.5-0.6 times carapace length, male P5 merus length 7.1-9.5 times width, female P5 merus length 7.9-8.8 times width (Figs 12 , 13A , 14F-J ). Male thoracic sternum flat, slightly concave; sternites 3, 4 widest. Male pleon with triangular telson and all 6 somites free; somites 2, 3 widest; surface of somites smooth (Fig. 13B ). G1 straight, distal part relatively shorter, sharp tip (Fig. 15E-H ).

Etymology.

The term " tenuis ", which means thin in Latin, is used for the slender ambulatory legs. The name is used as a noun in apposition.

Remarks.

Scyramathia tenuipes sp. nov. is superficially similar to S. carpenteri , but there are several important differences between the two species. Firstly, all the adult specimens of S. tenuipes sp. nov. examined have relatively less distinct plates on the carapace (Figs 12 , 13A ) (versus adult S. carpenteri usually have more prominent plates on the carapace; Figs 3 , 4A , 5A , 7A, C , 9A-I ). More significantly, it also has distinctly longer and more slender ambulatory legs, with the P2 meri length of all the male specimens longer or subequal in length (1.0-1.4 times) to the carapace length, and the P5 meri length 7.1-9.5 times longer than the width (Figs 12 , 13A , 14F-J ) (versus S. carpenteri has relatively shorter and less slender ambulatory legs, with the P2 meri of all male specimens typically subequal in length (0.7-1.1 times) to the carapace length, and the P5 meri length 4.2-7.3 times the width; Figs 3 , 4A , 5A , 14A, B ). This character is consistent in all the adult male and female specimens examined. The pterygostomial region of adult S. tenuipes sp. nov. has relatively more distinct granules (Fig. 13B ) compared to the more plate-like granules on that of adult S. carpenteri (Figs 4B , 5B , 6C , 7B, D ); and the distal part of the G1 of S. tenuipes sp. nov. is always relatively shorter (Fig. 15E-H ) compared to the longer ones of S. carpenteri (Fig. 8C-F ).

An unpublished genetic study by the first author comparing S. tenuipes sp. nov. with S. carpenteri , S. hertwigi , S. umbonata and other Rochinia species shows small but consistent differences that indicate we are dealing with a recent but separate species. A total of five genes, three mitochondrial genes: COI, 12S, 16S, and two nuclear genes: 18S and H3, were used for the molecular analysis in this unpublished work. The cytochrome oxidase I (COI) dendrogram for S. tenuipes sp. nov. and S. carpenteri shows a consistent 0.3% difference between them whereas the differences between the other Scyramathia and Rochinia species ranged from 1.3-10.9 %. Significantly, the phylogenetic tree from the Maximum Likelihood analysis shows an 87% support for S. tenuipes sp. nov. and S. carpenteri as separate clades.

The type locality of S. tenuipes sp. nov. is an interesting area in the Mediterranean. The Alboran Sea is at the western narrow part of Mediterranean that ends at the Strait of Gibraltar. The complex circulation of the waters through this very narrow strait of approximately 14 km, is known to play a key role in regulating the gene flow for a number of benthic species ( Palero et al. 2011). The peculiar hydrographic features of the Strait of Gibraltar were established since the end of the Messinian (upper Miocene) about 5.4 million years ago, after a period of very low sea level of 500,000 years where the strait was dry, and the Mediterrannean Sea was completely closed. Between Spain and Morocco, the very narrow strait has several choke points not deeper than 350 m that seriously affects the water currents. The surface Atlantic waters are entering at speeds varying from 1 to 2 knots, whereas the outflow of the Mediterranean waters nearer the sea bottom flows at a speed of 1.1 to 0.9 knots ( Millot 2005). The physical characteristics of these two opposite currents are also very different: the Atlantic surface water has a salinity of 36 g/l while the Mediterranean waters are denser at 38 g/l of salt. As a result of such conditions, the Alboran Sea has more influx from the Altantic Ocean than the rest of the Mediterranean basin ( Pascual et al. 2016). These peculiar oceanographical conditions could explain why S. tenuipes sp. nov. is most common in the Alboran Sea and not in the rest of Mediterranean or even in the main Atlantic waters adjacent. In the Mediterranean, S. tenuipes sp. nov. is known only from the western part of Mediterranean along the coast of Spain (Marco-Herero et al. 2015; Palero pers. comm.). The unusual oceanographic features in the Alboran Sea are what the species prefers. A study by Tortonese (1964) on the Mediterranean fish fauna have shown that the fish fauna differs in the different regions in the Mediterranean, for example the scorpionfish, Trachyscorpia cristulata echinata ( Köhler, 1896) ( Sebastidae ), is found only in the western part of Mediterranean, which is also observed by submersible during the Cyanalboran cruise (Zibrowius pers. comm.). It has also been discussed by d’Udekem d’Acoz (1999) that there are crustacean species that showed variations in morphological differences between the Atlantic and Mediterranean populations with unknown, continuous or absence of intermediate populations in between (see d’Udekem d’Acoz 1999: table 1). These morphological differences due to the geographical distribution are linked to the different physical characteristics of the Atlantic and Mediterranean waters ( d’Udekem d’Acoz 1999). However, it is likely that these species might be separate ones, as in this case, which requires more study.

There are various records of S. tenuipes sp. nov. as " S. carpenteri ", and while A. Milne-Edwards and Bouvier (1899, 1900) and Bouvier (1922, 1940) state that S. carpenteri was not known from the Mediterranean, d’Udekem d’Acoz (1999) noted that a Mediterranean specimen was figured by Dieuzeide (1955). The figure of the Mediterranean specimen by Dieuzeide (1955: fig. 9), shows an animal with long and slender ambulatory legs, weak plates on carapace, and relatively straight and slightly divergent pseudorostral spines, diagnostic characters of S. tenuipes sp. nov. (Figs 12 , 13A ). Subsequently, Dieuzeide (1960) commented that the species was commonly found among the bamboo coral, Isidella elongata (Esper, 1788) ( Isididae : Alcyonacea ) in the Mediterranean. Some of the specimens of S. tenuipes sp. nov. that were examined in this study were found with unidentified deep-sea anemones attached on their carapace.

Distribution.

Scyramathia tenuipes sp. nov. is known from its type locality, the western Mediterranean Sea, with possible records from Algeria ( Dieuzeide 1955), Azores, north of Sao Jorge in Portugal, and Sahara beach (A. Milne-Edwards and Bouvier 1894, 1899, 1900; Bouvier 1940), Morocco (A. Milne-Edwards and Bouvier 1900; Sivertsen and Holthuis 1956; Fransen 1991), and Mauritania (A. Milne-Edwards and Bouvier 1900).

Figures

Figure 3. Illustration of Scyramathia carpenteri (Norman, in Thomson 1873), " sandy chalk of Holtenia ground ", overall dorsal view. (After Norman, in Thomson 1873: fig. 35).

Figure 4. Scyramathia carpenteri (Norman, in Thomson 1873), lectotype male (21.6 x 15.9 mm) (NHM 1907.8.28.3), " Holtenia ground " (= between north Scotland and the Faeroe Islands). A. overall dorsal view; B. overall ventral view; C. lateral view of carapace.

Figure 5. Scyramathia carpenteri (Norman, in Thomson 1873), male (41.3 x 34.0 mm) (NHM 1983.449), North Sea. A. overall dorsal view; B. overall ventral view; C. lateral view of carapace.

Figure 6. A. Scyramathia carpenteri (Norman, in Thomson 1873), male (35.0 x 27.1 mm) (NHM 1981.108), North Sea; B-F. S. carpenteri (Norman, in Thomson 1873), male (41.3 x 34.0 mm) (NHM 1983.449), North Sea. A, B. lateral view of carapace; C. ventral frontal surface of carapace; D. male thoracic sternum view; E. dorsal surface of male left chela; F. posterior ventral view of male pleon.

Figure 7. Illustration of Scyramathia carpenteri (Norman, in Thomson 1873). A, B. lectotype male (21.6 x 15.9 mm) (NHM 1907.8.28.3), " Holtenia ground " (= between north Scotland and the Faeroe Islands); C, D. paralectotype female (13.0 x 8.4 mm) (NHM 1911.11.8.377), same locality as lectotype. A, C. dorsal view of carapace; B, D. ventral frontal surface of carapace.

Figure 8. Illustration of Scyramathia carpenteri (Norman, in Thomson 1873). A, C-H. lectotype male (21.6 x 15.9 mm) (NHM 1907.8.28.3), " Holtenia ground " (= between north Scotland and the Faeroe Islands); B. paralectotype female (13.0 x 8.4 mm) (NHM 1911.11.8.377), same locality as lectotype. A, B. lateral view of carapace; C. ventral view of G 1; D. ventral view of distal portion of G 1; E. dorsal view of G 1; F. dorsal view of distal portion of G 1; G. ventral view of G 1; H. dorsal view of G 2. Scale bars: 1 mm.

Figure 9. Variation of plate-like structures on carapace on Scyramathia carpenteri (Norman, in Thomson 1873). A. lectotype male (21.6 x 15.9 mm) (NHM 1907.8.28.3), " Holtenia ground "; B, G. female (22.4 x 17.2 mm, 35.8 x 29.0 mm, respectively) (NHM 1978.99), North Sea; C. male (41.3 x 34.0 mm) (NHM 1983.449), North Sea; D, E, H, I. male (28.2 x 22.7 mm, 37.1 x 30.5 mm, 24.6 x 17.2 mm, 33.0 x 25.7 mm, respectively) (NHM 1978.99), North Sea; F. male (35.0 x 27.1 mm) (NHM 1981.108), North Sea.

Figure 12. Colour in life of Scyramathia tenuipes sp. nov., holotype male (33.9 x 26.3 mm) (ICMD 288), Mediterranean Sea (Credits: MacPherson E & Abello P).

Figure 13. Scyramathia tenuipes sp. nov., holotype male (33.9 x 26.3 mm) (ICMD 288), Mediterranean Sea. A. overall dorsal view; B. overall ventral view; C. lateral view of carapace.

Figure 14. Dorsal view of P 5. A, B. Scyramathia carpenteri (Norman, in Thomson 1873); A. male (41.3 x 34.0 mm) (NHM 1983.449), North Sea; B. ovigerous female (35.8 x 29.0 mm) (NHM 1978.99), Atlantic Ocean; C, D. S. hertwigi Doflein, in Chun 1900; C. male (34.6 x 27.3 mm) (NHM 1924.7.19.1 - 3), South Africa; D. female (24.5 x 18.4 mm) (SAM-A 47872), South Africa; E, S. umbonata (Stimpson, 1871), female (36.7 x 27.9 mm) (NSMT-Cr 7178), off Suriname; F-J. S. tenuipes sp. nov.; F. holotype male (33.9 x 26.3 mm) (ICMD 288), Mediterranean Sea; G. paratype male (29.7 x 22.0 mm) (ICMD 000707), Mediterranean Sea; H. paratype male (32.0 x 25.4 mm) (ZRC 2019.1636), Mediterranean Sea,; I. paratype ovigerous female (31.2 x 24.6 mm) (ICMD 000708), Mediterranean Sea,; J. paratype ovigerous female (32.2 x 25.8 mm) (ZRC 2019.1635), Mediterranean Sea.

Figure 15. A-D. Scyramathia hertwigi Doflein, in Chun 1900, paralectotype male (24.7 x 19.0 mm) (ZMB 13700), Agulhasstrom [= Agulhas current], left G 1; E-H. Scyramathia tenuipes sp. nov., holotype male (33.9 x 26.3 mm) (ICMD 288), Mediterranean Sea, left G 1. A, E. ventral view; B, F. ventral view of distal portion; C, G. dorsal view; D, H. dorsal view of distal portion. Scale bars: 1 mm.