Amphithrax aculeatus (Herbst, 1790)

Parasram, Nadeshinie, Santana, William, Valles, Yvonne, Windsor, Amanda M. & Valles, Henri, 2024, Morphological and molecular support for Amphithrax verrucosus (H. Milne Edwards, 1832) and Amphithrax aculeatus (Herbst, 1790) (Crustacea, Decapoda, Brachyura) as valid species, Zoosystematics and Evolution 100 (1), pp. 15-30 : 15

Amphithrax aculeatus (Herbst, 1790)

Figs 2C , 3A-D , 5A, C, D , 6A-D

Cancer aculeatus Cancer aculeatus Herbst, 1790: 248, pl. XVIII, fig. B, pl. XIX, fig. 104 [type-locality: Americas (probably between Florida and Venezuela); holotype (ZMB Herbst 0134) and paralectotype (ZMB Herbst 0079) in Berlin Museum]. - Desmarest (1825: 151).

Cancer spinipes Cancer spinipes Herbst, 1790: 241, pl. XVII, fig. 94 [type locality: probably West Indies; type: probably lost]. - Desmarest (1825: 151).

Mithrax aculeatus - H. Milne Edwards 1832: class 7; 1834-1840: 321; Schomburgk 1848: 65; Stimpson 1860: 188; Desbonne and Schramm 1867: 5; A. Milne-Edwards 1875: 102; Ng et al. 2008: 120; Windsor and Felder 2014: 163, figs 3G, 4H.

Mithrax pilosus Rathbun, 1892: 262, pl. 39 [type-locality: Abaco Island, Bahamas; holotype (USNM 16299) and paratypes (USNM 16299) in National Museum of Natural History, Washington, D.C.]. - Rathbun 1901: 66; 1921: 83; Nutting 1919: 75; Rodríguez 1980: 287; Abele and Kim 1986: 47, 522 fig. c; Wagner 1990: 25-29, figs 28-31; Carmona-Suárez and Poupin 2016: 373, fig. 6H.

Mithrax (Mithrax) aculeatus - Young, 1900: 90.

Mithrax (Mithrax) pilosus - Rathbun, 1925: 394, pl. 138, fig. 3; 1933: 29; Powers 1977: 57; Lira et al. 2013: 55, tab.1.

Amphithrax aculeatus - Windsor & Felder, 2017: 1; Poupin 2018: 192-193, fig. 210; Questel 2019: 16, unnumbered figure; Parasram et al. 2023: 20, fig. 9B.

Material examined.

Type material. Paralectotype of Cancer aculeatus Herbst, 1790: Americas • dry carapace only, ZMB Herbst 79. Holotype of Mithrax pilosus Rathbun, 1982: Bahamas, Abaco Island, Albatross Research Vessel • ♂ (CW: 30.0; CL: 28.0 mm) (USNM 16299), 26°27'59.99"N, 77°04'60.00"W . Paratypes: Idem, 2 ♂♂, 1 juv. ♀ (CW: 29.0; 29.0; 19.0; mm; CL: 26.0; 26.0; 18.0 mm) (USNM 16299).

Additional material.

Puerto Rico, Playa de Ponce, Lighthouse Reef • 1 ♂, 1 juv. ♂ (CW: 23.0; 9.0 mm; CL: 21.0; 9.0 mm) (USNM 24091), 18°00'39"N, 66°41'14"W . St. Croix, Christiansted Harbour • 1 ♀ (CW: 42 mm; CL: 35 mm) (USNM 72827), 17°44'47.9004"N, 64°42'11.5236"W . Virgin Islands, St. Croix, Buck Island , 1 ♂ (CW: 28 mm; CL: 25 mm) (USNM 73318), 17°47'14"N, 64°37'15"W . Guadeloupe, Anse Babin , KARUBENTHOS 2012 • 1 ♂ (MNHN-IU-2013-5929), 16°20'26.9988"N, 61°31'32.9988"W . Barbados • 1 ♂ (CW: 105.0 mm; CL: 87.0 mm) (USNM 1519303), 13°04'30.73"N, 59°36'12.49"W . Palm Court , St. Michael • 3 ♂♂, 1 juv. ♀ (CW: 10.0; 11.0; 11.4; 53.8 mm; CL: 11.0; 12.0; 44.0 mm) (BLSZ 217), nearshore rubble, 13°04'30.73"N, 59°36'12.49"W . Idem, 1 ♂, (CW: 37.0 mm; CL: 32.0 mm) (BLSZ 331). Idem, 1 juv. ♀, (CW: 34.4 mm; CL: 30.0 mm) (BLSZ 220). Idem , 1 juv. ♀, (CW: 33.4 mm; CL: 30.0 mm) (BLSZ 221). Idem , 1 ♂ (CW: 32.0 mm; CL: 28.0 mm) (BLSZ 222). Idem , 1 juv. ♀ (CW: 28.0 mm; CL: 24.0 mm) (BLSZ 223). Idem , 1 juv. ♀ (CW: 34.0 mm; CL: 29.0 mm) (BLSZ 267). Idem , 1 juv., ♀ (CW: 16.2 mm; CL: 16.0 mm) (BLSZ 268). Drill Hall , St. Michael • 1 juv. ♀, 1 ♂ (CW: 29.6; 24.7 mm; CL: 26.0, 21.0 mm) (BLSZ 120), nearshore rubble, 13°04'36.30"N, 59°36'26.63"W . Idem, 3 ♂♂, (CW: 12.4;12.5; 7.8 mm; CL: 13.0; 14.0; 9.6 mm) (BLSZ 129). Idem, 1 juv., ♀ (CW: 13.0 mm; CL: 13.3 mm) (BLSZ 252). Idem , 3 ♂♂, 1 juv., ♀ (CW: 22.5; 10.3; 10.4; 11.0 mm; CL: 20.0; 10.0; 10.0; 11.0 mm) (BLSZ 269). Schooner Bay , St. James • 2 ♂♂, 1 ♀ (CW: 10.6; 30.5; 40.5 mm; CL: not taken) (MZUSP 40878, 40884), nearshore rubble, 13°14'48.24"N, 59°38'40.90"W .

Diagnosis.

Carapace with acute spines dorsally, mainly in gastric, branchial, cardiac regions. Third antennal segment with long spine distolaterally, distinctly visible dorsally. Chelipeds slender; carpus with strong, sharp spines. Palm of chela with 4-5 spines on the upper margin. Propodus of pereopods with two to four spines on the proximal half. Carapace olive green to brown in colour.

Remarks.

Herbst (1790: 248) referred to Cancer aculeatus as a "very rare American crab", but Amphithrax aculeatus is very abundant in Barbados. It is possible that the Herbst assessment of the rarity of this species is due to sampling biases (methodology used and sampling time), which resulted in a small number of specimens collected and deposited to the Berlin Museum ( Tavares and Mendonça 2022).

In the same work, Herbst (1790) described Cancer spinipes, and both its description and figure resemble A. verrucosus . However, Windsor and Felder (2014) selected the lectotype of Cancer aculeatus Herbst, 1790 as the neotype for Cancer spinipes Herbst, 1790, establishing these names as objective synonyms. Due to lack of material for Cancer spinipes Herbst, 1790, we have opted to maintain its status as a synonym of A. aculeatus . This decision is based on the need for nomenclatural consistency in the absence of more definitive data. While Herbst (1790) did not specify any locality for Cancer spinipes, which he referred to as a "Chinese crab" in the description (Herbst 1790: 241 "Der Schild dıefer chinesischen Krabbe ift herzförmig”), Desmarest (1825) cited both Cancer spinipes and Cancer aculeatus as originating from the East Indies. We believe that this is a labelling mistake (common at that time) given that both species are endemic to the Western Atlantic.

Amphithrax aculeatus can be separated from A. verrucosus by: (i) the carapace densely setose, forming a velvet-like cover in both juvenile and adult specimens (Figs 3A, B , 5C , 6 A-D ) (vs. carapace almost without setae in fully developed specimens, few setae concentrated laterally; in juveniles, carapace interspace with long and short dark setae, not forming a velvet-like cover in A. verrucosus ; Figs 4A, B , 5B , 6 E-H ); (ii) anterolateral margins of the carapace with six spines, excluding the orbital spine, where the first, second and third anterolateral spines are accompanied by an accessory spine (Figs 3A , 6A, D ) (vs. anterolateral and posterior margins of the carapace with six to eight spines, excluding the orbital spine, where the first and second anterolateral spine are accompanied by accessory spines in A. verrucosus ; Figs 4A , 6E, G ); (iii) third antennal segment with long spine distolaterally, distinctly visible dorsally (Fig. 3B ) (vs. third antennal segment with short spine distolaterally, not visible dorsally in A. verrucosus ; Fig. 4B ); (iv) chelipeds slender in adults, carpus with several strong, acute spines and palm of chela with four or five spines on the upper margins (Figs 3A , 6A, C ) (vs. chelipeds more massive, especially in adult males, carpus without spines dorsally, with one to three blunt teeth on the inner margin, and palm of chela smooth; Figs 4A , 6E, G ); (v) propodus of pereopods with two to four spines on the proximal half (vs. propodus of pereopods without spines in A. verrucosus ); (vi) third maxilliped covered with short setae (vs. third maxilliped without setae in A. verrucosus ); (vii) dorsal surface of pleon in males and females are covered in small thick setae (vs. dorsal surface of pleon in males and females without setae in A. verrucosus ; (viii) G1 long, slender, dorsoventrally flattened, with the proximal third slightly curved towards mesial line, lateral margin with pappose setae at the base; tip triangular with rounded mesial lobe (Fig. 3C, D ) (vs. G1 long, robust, slightly dorsoventrally flattened, with the proximal third slightly curved towards mesial line, lateral margin with pappose setae from base to distal third of shaft, tip V-shaped, with fold just below tip in A. verrucosus ; Fig. 4C, D ; see also Wagner (1990) and Lianos et al. (2021); (ix) dorsal and ventral surfaces of live specimens are olive green to brown in colour with whitish fingers of chela (Figs 3A , 6A-C ) (vs. dorsal surface of live specimens predominantly maroon in colour and mixed with white spots on ventral surface, in ventral view, only tips of fingers are white in A. verrucosus ; Figs 4A , 6E-H ). It is worth pointing out that Wagner’s (1990: 27, fig. 30) illustration of an Mithrax pilosus G1 is that of a young specimen of A. aculeatus .

Ontogenetic intraspecific variations in A. aculeatus from juveniles to adults are: spines on the carapace, carpus, and pereiopods become larger and more acute, but can be broken in the larger individuals. In some juvenile specimens, the gastric region of the carapace has more sparse setae than other regions and the dorsal surface also has the presence of flattened granules, five spines on anterolateral margins, with small and blunt accessory spines. In contrast, adults have the dorsal and ventral surface of the cephalothorax covered in short tuft setae, which has the appearance of a velvet mat; the granules on dorsal surface of the carapace develop into spines; anterolateral margins with six spines that are accompanied with well-developed accessory spines that are spiniform in shape. The palm of chelipeds in juveniles can have one to four spines, while in adults, the palm has three to six spines.

Parasram et al. (2023) reported Amphithrax aculeatus being found in close association with A. verrucosus , Mithraculus coryphe (Herbst, 1801), M. forceps A. Milne-Edwards, 1875, Eriphia gonagra (Fabricius, 1781) and Pachygrapsus transversus (Gibbes, 1850). Specimens of A. aculeatus were collected by hand and with caged crab traps on the west and south coasts of Barbados. Amphithrax aculeatus females collected in Barbados are generally larger than males (see material examined). No sexually mature females were found.

Due to the recurrent misidentifications between A. aculeatus and A. verrucosus in literature, determining the geographic distribution for these species has proved to be challenging. Nevertheless, based on the morphological characteristics provided by some authors, it seems that A. aculeatus has a more restricted geographic range, which encompasses the insular Caribbean. For instance, most of the material examined by Rathbun (1925: 395, Fig. 5 ) (under the name Mithrax pilosus ) was collected from Caribbean islands, except for two specimens (one male and one female) from Venezuela. The first mention of these specimens was made by von Martens (1872: 82), but this could be a labelling mistake since Caracas is not a coastal city. These specimens were deposited in the Berlin Museum. In addition, A. Milne-Edwards (1875: 103) also mentioned two specimens of A. aculeatus collected in Vera Cruz, Mexico by M. Brémond. Contacting both ZMB and MNHN was not successful in locating these materials, therefore, these specimens are herein classified under A. verrucosus , given the prevalence of this species in Central America.

As a result of Windsor and Felder’s (2014) revision, multiple collections modified their taxonomic records to align with A. aculeatus , which resulted in the renaming of many specimens previously identified as A. verrucosus (see USNM and MNHN online catalogues). Based on our re-examination of the literature and materials from different localities, we proposed the following update range for the two species: A. aculeatus is island endemic with a northern limit of Florida (Tortugas) and a southern limit of Barbados, whereas A. verrucosus has a northern limit of USA (South Carolina) and a southern limit of Brazil.

Colouration.

In its natural habitat, the carapace of A. aculeatus exhibits an olive green to brown hue; but the carapace could be spotted with large beige spots (MNHN-IU-2013-5929) especially in younger individuals. The chelipeds are predominantly green (darker or lighter) with black spots on the palm, fingers are whitish (Figs 3A , 6 A-D ). Pereopods are brown (light to dark) or green.

Distribution.

Western Atlantic: USA (Florida, Dry Tortugas), Bahamas, Cuba, Puerto Rico, British Virgins Islands, St. Thomas, St. Croix, St. Martin, St. Barthélemy, Antigua, Guadeloupe, Martinique, and Barbados ( Stimpson 1860; Rathbun 1925; Carmona-Suárez and Poupin 2016; Poupin 2018; present study).

Figures

Figure 2. A. BI molecular phylogenetic tree for Amphithrax verrucosus, A. aculeatus and other selected species within the family Mithracidae MacLeay, 1838. Based on GTR + G nucleotide substitution model on the concatenated dataset for two mitochondrial (12 S, 16 S) and one nuclear (ITS- 1) genes, represented as a maximum likelihood phylogram with Bayesian posterior probabilities and maximum likelihood bootstrap values (black diamond = ≤ 50 % support, * = 16 S sequences only). Note: ULLZ's 9148 and 4534, of Windsor and Felder (2014) and 13596 all re-identified as Amphithrax verrucosus (H. Milne Edwards, 1832); B. Amphithrax verrucosus (H. Milne Edwards, 1832), male (CW: 40.7 mm; CL: 29.5 mm), Barbados (BLSZ 218); C. Amphithrax aculeatus (Herbst, 1790), juvenile female (CW: 53.8 mm; CL: 44.0 mm), Barbados (BLSZ 217).

Figure 3. Amphithrax aculeatus (Herbst, 1790) adult male (BLSZ 331). A. Habitus, dorsal; B. Ventral view, locality: Barbados; C. Pleonal view of right G 1 (BLSZ 222); D. Distal third of the right G 1. Scale bars: 20 mm (A, B); 10 mm (C). Photos: Nadeshinie Parasram.

Figure 4. Amphithrax verrucosus (H. Milne Edwards, 1832) adult male (BLSZ 218). A. Habitus, dorsal; B. Ventral view, locality: Barbados; C. Pleonal view of left G 1 (BLSZ 228); D. Distal third of left G 1. Scale bars: 20 mm (A, B); 10 mm (C). Photos: Nadeshinie Parasram.

Figure 5. Type specimens. A. Paralectotype of Cancer aculeatus, Herbst, 1790, dry preserved carapace without setae and with most of the spines broken (ZMB Herbst 79), locality: Antilles; B. Holotype of Mithrax plumosus Rathbun, 1901 (USNM 23775), ovig. female (CW: 37.0 mm; CL: 29.0 mm), locality: Puerto Rico; C. Holotype of Mithrax pilosus Rathbun, 1892, setae on carapace removed (USNM 16299), male (CW: 30.0 mm; CL: 28.0 mm), locality: Bahamas; D. Distal third of the right G 1 of the holotype of Mithrax pilosus (USNM 16299) in pleonal view. Photos: A Kristina von Rintelen. B, C, D Amanda Windsor.

Figure 6. Colour in life. Young female of Amphithrax aculeatus (Herbst, 1790) (BLSZ 217), Barbados. A. Habitus dorsal view; B. Ventral view. Adult male of Amphithrax aculeatus (Herbst, 1790) (MNHN-IU- 2013 - 5929), Guadeloupe; C. Habitus, dorsal view; D. Ventral view. Adult male of Amphithrax verrucosus (H. Milne Edwards, 1832) (GIC 072), Venezuela; E. Habitus, dorsal view; F. Ventral view. Female of Amphithrax verrucosus (H. Milne Edwards, 1832) (BLSZ 328), Barbados; G. Habitus, dorsal view; H. Ventral view. Scale bars: 20 mm. Photos: A, B, G, H. Nadeshinie Parasram. C, D. Joseph Poupin. E, F. William Santana.