Dromia erythropus (Edwards in Catesby, 1771)

(Figs. 5A–D, 6A–D)

Cancer erythropus Edwards in Catesby, 1771: 37 [Type locality: unknown].

Dromia gouveai Melo & Campos Junior, 1999: 281, fig. 3A, B [Type locality: Jeribatuba, Itaparica Island, near Salvador, Bahia, Brazil].

Trindade and Martin Vaz specimens. 1 juvenile female (MZUSP 33351), Brazil, off Espírito Santo, Trindade Island, Enseada dos Portugueses, SECON, 20º30’20.9’’S, 29º18’43.7’’W, J.B. Mendonça coll., 29.iv.2014, 9.9 m. 1 juvenile male (MZUSP 33349), ibidem, Farol, 20º29’52.3’’S, 29º19’15.6’’W, J.B. Mendonça coll., 17.iv.2014, 13.3 m. 1 ovigerous female (MZUSP 42512), ibidem, 23.x.2014, 12.5 m. 1 megalopa (MZUSP 40354), ibidem, 22.iv.2014, 13.7 m. 1 juvenile female (MZUSP 40356), ibidem, Ponta da Calheta, 20º30’18.72’’S, 29º18’31.6’’W, J.B. Mendonça coll., 29.iv.2014, 15.9 m. 1 juvenile female (MZUSP 40360), ibidem, 25.vi.2015, 16.9 m. 1 juvenile male (MZUSP 40362), ibidem, Parcel das Tartarugas, 20º31’11.86’’S, 29º18’0.06’’W, J.B. Mendonça coll., 2.ii.2019, tide pool, 1 m. 1 juvenile male (MZUSP 40355), ibidem, 3.ii.2019, tide pool, 1 m. 1 juvenile (MZUSP 40357), ibidem, 20º31’01.3’’S, 29º17’56.9’’W, J.B. Mendonça coll., 3.vii.2019, 12 m. 1 juvenile male (MZUSP 40361), ibidem, 10.ii. 2019, bated trap, tide pool, 1 m. 1 juvenile (MZUSP 39699), ibidem, Enseada das Orelhas, 20º29’40.2’’S, 29º20’32.9’’W, J.B. Mendonça coll., 8.viii.2018, 9 m. 1 juvenile male (MZUSP 33348), ibidem, 1.iv.2014, 8.9 m. 1 juvenile male (MZUSP 40358), Martin Vaz, Ilha do Norte, 20º28’11.51’’S, 28º51’25.01’’W, J.B. Mendonça coll., 29.i.2019, 19.1 m.

Size of largest male: cl 19 mm, cw 23 mm; largest female: cl 23 mm, cw 26 mm.

Comparative material examined. Dromia erythropus: Brazil: Central Atlantic: 1 ovigerou female (MZUSP 16990), São Pedro and São Paulo Archipelago, 1146 km off the coast of northeastern Brazil, in lobster traps, F. Moraes coll., vii.2004. Ceará: 1 male (MZUSP 16955), Canopus Bank, 120 miles off the coast of Fortaleza, J. Coltro coll., viii.2005, rocky bottom, 240–260 m. Pernambuco: 1 male, 1 female (MZUSP 13732), Tamandar, R.L. Moura and Francini Filho coll., 23.i.1999. Bahia: 1 male (MZUSP 41182), Minerva Bank, 17º03.108’S, 37º37.216’W, J. Coltro coll., 12.viii.2012, 69 m. Espírito Santo: 1 male (MNHN), Vitória–Trindade Seamount Chain, R/V “Marion Dufresne”, TAAF MD55/Brésil Expedition, Dogaressa Bank, stn 25 DC43, 20º50.9’S, 33º44.6’W, 17.v.1987, 63 m. São Paulo: 1 female (MZUSP 17551), Barra de Santos, 50–60 m. Santa Catarina: 1 male (MZUSP 6182), Ganchos de Fora, O. Barbosa coll., 22.x.1981. Dromia gouveai: Brazil: Bahia: holotype male, cl 90 mm, cw 130 mm (MZUSP 10222) [junior synonym of D. erythropus], “Geribotuba”, Salvador, Bahia [most probably Jeribatuba, Itaparica Island, near Salvador, Bahia]. Rio de Janeiro: 1 male (MZUSP 2876) Ilha Grande, stn 211, 21.vii.1966, detritic bottom, 13.5 m. 1 male paratype (MZUSP 5526), Saco do Mamangu, Santos, state of São Paulo [actually Saco do Mamangu, Paraty, state of Rio de Janeiro]. Dromia marmorea Forest, 1974: 1 male (MZUSP 291), Mediterranean Sea, no further details. Dromia personata (Linnaeus, 1758): Portugal: 1 female (MZUSP 41179), Algarve, Sagres, in dark cave, H. Zibrowius coll., 6.ix.1986, 6 m [M. de Saint Laurent don., J. Forest det. 1987]. France: 1 juvenile female (MZUSP 41180), Banyuls-sur-mer, Cap l’Abeille, coralligenous bottoms, J-M. Amouroux coll., vi.2001.

Distribution. Dromia erythropus is the only western Atlantic species in the genus, where it is known to occur from Bermuda southward to Brazil (Maranhão to Santa Catarina). This is the first record of D. erythropus from the São Pedro and São Paulo Archipelago, Canopus Bank off Ceará, Trindade and Martin Vaz Archipelago, and the Vitória–Trindade Seamount Chain (Dogaressa Bank). The species has also been recorded from the oceanic islands of Fernando de Noronha (Viana et al. 2003), Ascension and Saint Helena (Manning & Chace 1990).

Ecological notes. Dromia erythropus inhabits hard bottoms, including coral reefs, rocks, broken shell beds and loose rubble in depths of 1 to 364 m (Felder et al. 2009). It leaves in association with sponges, ascidians and soft corals carried on the dorsal surface of the carapace (Fig. 5A, B, D). The larval phase consists of five zoeal and one megalopa (Fig. 5C) stages and the development to the first crab stage takes about 28 to 30 days in laboratory conditions (Laughlin et al. 1982). The small juvenile MZUSP 40357 from Trindade was already carrying a sponge (5.9 mm 9.0 mm) at cl 2.2 mm, cw 2.2 mm, almost four times its width. The female MZUSP 16990 from the São Pedro and São Paulo Archipelago was carrying eggs and also a sperm plaque around the spermathecal apertures (see also Guinot & Tavares, 2003). The plaque is probably a spill and/or reflux of male material, which in D. erythropus and Moreiradromia antillensis (Stimpson, 1858) is made of protein granules and polysaccharides (Bento et al. 2019; McLay 2019). Dromia erythropus is occasionally caught in fish traps and spiny lobsters gillnets (Tagliafico et al. 2005; Giraldes et al. 2015).

Remarks. In male and female juveniles of Dromia erythropus the accessory tooth (between the second and third anterolateral teeth– exorbital tooth excluded) appears as a lobe. Juvenile males (e.g. MZUSP 33349, cl 19 mm, cw 23 mm) have paired, uniramous vestigial pleopods on somites 3–5 showing as tiny membranous buds (adults with G1, 2 only). Juvenile females (e.g. MZUSP 33351, cl 18 mm, cw 21 mm) have the genital openings on the P3 coxae appearing as tiny membranous circles and the spermathecal apertures at the end of the sternal sutures 7/8 closed.

Juveniles of D. erythropus and Moreiradromia antillensis are frequently confused with each other. Criteria to distinguish between male and female juveniles of the two species are given below under M. antillensis.

In the megalopa of D. erythropus the metabranchial region of the carapace beneath P4 and P5 is already covered with a particularly short tomentum, whereas the other parts of the carapace are densely tomentose. P4 and P5 are both reduced in size and carried subdorsally; P5 is remarkably longer than P4. These characteristics remain in full grown specimens.

Dromia gouveai vs D. erythropus (Fig. 6A–D). Melo & Campos Junior (1999) described D. gouveai based on two males, being the holotype from “Geribotuba”, Salvador, Bahia (most probably Jeribatuba, Itaparica Island, near Salvador, Bahia) and the paratype from “Saco do Mamangu”, Santos, state of São Paulo (actually Saco do Mamangu, Paraty, state of Rio de Janeiro) (Fig. 6C, D). Dromia gouveai purportedly differs from D. erythropus in that 1) the distance from the third anterolateral tooth of the carapace (exorbital tooth included) to the fourth tooth (accessory tooth) is less than that from the third to the second tooth (vs subequal intervals in D. erythropus); 2) the P5 merus is longer than the length of the propodus and carpus together (vs P5 merus shorter than propodus and carpus together in D. erythropus); and in that 3) the uropod is more developed in the former species (Melo & Campos Junior 1999).

However, reexamination of the type material of D. gouveai (Fig. 6C, D) showed that these characters are not consistent and cannot be used to differentiate D. gouveai from D. erythropus. The relative distance between the third to fourth (d3–4) and third to second (d3–2) teeth vary between specimens and even from one side of the carapace to the other (Table 3). In the holotype of D. gouveai the distance d3–4 is less indeed than d3–2 on the left side of the carapace, but the distances d3–4 and d3–2 are equal on the right side of the carapace. In the paratype of D. gouveai, but also in the female D. erythropus MZUSP 13732, the distance d3–4 is less than d3–2 on both sides of the carapace. In the male D. erythropus MZUSP 6182 the distance d3–4 is less than d3–2 on both sides of the carapace, whereas in the male D. erythropus MZUSP 13732 the distance d3–4 is greater than d3–2 on the right side but equal on the left side of the carapace (Table 3).

Contrary to Melo & Campos Junior (1999) the P5 merus maximum length is actually less than the length of the propodus and carpus together in both D. erythropus and D. gouveai (all measurements taken along the dorsal margins), and the uropod is not more developed in the later species than in the former (Table 3).

In the absence of other characters to separate the two species, D. gouveai is herein considered a junior synonym of D. erythropus.