(Fig. 21A–D)
Mithraculus forceps A. Milne-Edwards, 1875: 109, pl. 23, fig. 1 [Type locality: Cayenne, French Guiana].
Trindade and Martin Vaz specimens. 1 male (MZUSP 33739), Trindade Island, Enseada das Orelhas, 20°29’40.2”S, 29°20’32.9”W, J.B. Mendonça coll., 01.xi.2014, 12 m. 1 male, 1 female (MZUSP 39840), ibidem, 2.vii.2015, 14.7 m. 1 ovigerous female (MZUSP 39681), ibidem, 1.vii.2016, 9.2 m. 1 male (MZUSP 39853), ibidem, Ponta da Calheta, 20°30’18.72”S, 29°18’31.67”W, J.B. Mendonça coll., 20.x.2014, 17 m. 1 male, 1 female, 2 ovigerous female, 1 ju venile female (MZUSP 40741), ibidem, 20°30’19.5”S, 29°18’47.3”W, J.B. Mendonça coll., 26.vi.2012, 14.3 m. 1 ovigerous female (MZUSP 40602), 1 juvenile female (MZUSP 40245), ibidem, 24.xi.2017, 17 m. 1 male, 3 ovigerous females (MZUSP 39911), ibidem, 20°30’18.72”S, 29°18’31.6”W, J.B. Mendonça coll., 29.iv.2014, 15, 9 m. 1 ovigerous female (MZUSP 40568), ibidem, 24.vi.2017, 19.3 m. 1 male (MZUSP 39682), ibidem, 20°30’29.5”S, 29°18’37.0”W, J.B. Mendonça coll., 20.vi.2016, 8.2 m. 3 males, 6 ovigerous females (MZUSP 40586), ibidem, 20°30’16.59”S, 29°18’30.11”W, J.B. Mendonça coll., 30.i.2019, 15.1 m. 1 male, 1 juvenile female (MZUSP 33738), 1 juvenile female (MZUSP 40759), 1 male, 3 females (MZUSP 41131), ibidem, Enseada dos Portugueses, Farol, 20°29’52.3”S, 29°19’15.6”W, J.B. Mendonça coll., 8.iv.2014, 12.9 m. 3 males, 3 juvenile males, 1 juvenile (MZUSP 41132), 22.iv.2014, 13.7 m. 2 males, 4 ovigerous females (MZUSP 39637), ibidem, 25.vii.2018, 10 m. 1 male (MZUSP 40187), ibidem, 25.vii.2018, 10 m. 1 female (MZUSP 39859), ibidem, Enseada dos Portugueses, 20°30’17.7”S, 29°18’56.7”W, J.B. Mendonça coll., 18.iv.2014, 10.2 m. 1 male, 1 juvenile male, 1 juvenile (MZUSP 40703), ibidem, 20°30’20.9”S, 29°18’43.7”W, J.B. Mendonça coll., 29.iv.2014, 9.9 m. 1 ovigerous female (MZUSP 40561), ibidem, Ponta Norte, 20°29’18.7”S, 29°20’18.3”W, J.B. Mendonça coll., 31.vii.2018, 12.4 m. 1 male, 2 females (MZUSP 39919), ibidem, 2.vii.2015. 2 males, 1 male and 1 female juveniles (MZUSP 39827), ibidem, Ponta do Monumento, 20°30’10.3”S, 29°20’36.1”W, J.B. Mendonça coll., 3.vii. 2015, 15.5 m. 1 male, 3 juvenile males, 1 ovigerous female, 2 juvenile females (MZUSP 39619), ibidem, Ilha da Racha, 20°30’26.5”S, 29°20’48.0”W, J.B. Mendonça coll., 30.vii. 2018, 24.8 m. 3 males, 1 juvenile male, 1 female (MZUSP 39883), ibidem, Praia das Cabritas, 20°29’41.38”S, 29°19’39.99”W, J.B. Mendonça coll., 25.vi. 2015, 12 m. 1 damaged male (MZUSP 39847), 1 juvenile male (MZUSP 40669), Martin Vaz, Ilhote Principal, 20°28’26.98”S, 28°51’20.98”W, coralligenous sediment, C.H. Guimarães coll., 22.i.2012, 19.2 m.
Size of largest male: cl 15 mm, cw 17.5 mm; largest female: cl 12.9 mm, cw 14.9 mm.
Comparative material examined. Mithraculus forceps: United States: 2 males, 2 females (USNM 16046), Florida, Indian Key, along shore, low tide, no further details. Caribbean Sea: Grenada: 1 male (MZUSP 28066), Grand Anse Bay, 12°1’45.68”S, 61°46’18.67”W, L.R.L. Simone et al. coll., 8.x.2012, 10 m. Brazil: Central Atlantic: 3 males (MZUSP 41237), São Pedro and São Paulo Archipelago, Cabea da Tartaruga, W. Santana et al. coll., 18.ii.2009 to 5.iii.2009. Rocas Atoll: 1 juvenile male, 1 female (MZUSP 12476), R.L. Moura and R.S. Rosa coll. Paraíba: 3 males, 2 females (MZUSP 11804), Projeto Algas, stn 69-b, 6°46’S, 34°47’W, 19.v.1981, 18 m. 1 male (MZUSP 15524), João Pessoa, Ponta do Cabo Branco, M.F. C. Lima coll., 21.iii.2000. Fernando de Noronha Archipelago: 1 juvenile male (MZUSP 20561), 3°50’11”S, 32°23’53.4”W, L.R. Simone and C.M. Cunha coll., 8.iii.2009. 2 males (MZUSP 20540), ibidem, Praia do Porto, 3°50’S, 32°24’01.6”W, L.R. Simone and C.M. Cunha coll., 10.iii.2009. 1 juvenile male (MZUSP 34303), ibidem, Buraco da Raquel, next to the Port, L.R.L. Simone coll., 4.v.2013. Pernambuco: 1 male (MZUSP 32455), Tamandar, Praia de Tamandar, R. Silva coll., i.1990. Bahia: 7 males, 11 ovigerous females (MZUSP 41233), Minerva Bank, 17°03.108’S, 37°37.216’W, J. Coltro coll., 12.viii.2012, 69 m. Rio de Janeiro: 1 male, 1 female (MZUSP 20322), Búzios, Praia dos Ossos. 1 juvenile male, 6 ovigerous females, 1 juvenile female (MZUSP 21339), Maricá, Ilhas Maricás, M. Tavares coll., 21.iv.1985, on Schizoporella. 2 males, 2 juvenile females, 5 juveniles (MZUSP 2826), Angra dos Reis, Praia de Vila Velha, G.A.S. Melo coll., 14.vii.1966. 3 males, 2 juvenile males, 3 ovigerous females, 3 juvenile females (MZUSP 3662), Ilha Grande, Praia do Furado, G.A.S. Melo coll. 20.vii.1966.
Distribution. From North Carolina, through Gulf of Mexico, Caribbean Sea, north coast of South America to Brazil (Maranhão to Santa Catarina) (Melo 1996; Serejo et al. 2006; Bouzon & Freire 2007; Felder et al. 2009). Brazilian oceanic islands: known from São Pedro and São Paulo, Rocas Atoll, Fernando de Noronha and Trindade and Martin Vaz. Mithraculus cf. forceps has been reported from the late Pleistocene of Jamaica (Klompmaker et al. 2015, and references therein).
Ecological notes. Mithraculus forceps is commonly associated with different substrata, including the sponges Amphimedon viridis Duchassaing & Michelotti and Stematumenia strobilinia (Lamarck), the calcareous bryozoans Schizoporella unicornis (Johnston in Wood) and S. errata (Waters), Porites spp. corals, sand reefs of Phragmatopoma caudata Krøyer, mangroves (Caribbean coast), seagrass (Thalassia) and macroalgae, and also has been found under stones and in coralligenous sediment, from the tide mark down to 100 m (Rodríguez 1980; Gore et al. 1981; Williams 1984; Melo 1996; Rieger & Giraldi 1996; Mantelatto & Souza-Carey 1998; Morgado & Tanaka 2001; Cobo 2002; Alves et al. 2012b, 2012 c, 2013; Lane-Medeiros et al. 2021). Mithraculus forceps is very common in Trindade (seemingly less so in Martin Vaz), where it has been found between 8 and 24 m. It also has been reported to be the commonest crab species in insular coastal habitats (Alves et al. 2012b). Mithraculus forceps is a prey for 12.9 mm (Cobo 2002, 2006; Cobo & Alves 2009). Females can use stored sperm to fertilize eggs for more than one consecutive spawn without mating (Penha-Lopes et al. 2006). Ovigerous females have been reported all year-round, which translates into constant larval supply. The mean larval duration from hatching to crab I is of about 8.3 ± 0.5 days; the duration for the zoea I and II stages is of about 2 days each, and 3–8 days for the megalopa in laboratory conditions (Rhyne et al. 2005). Larval duration may be longer (over 14 days) depending on the rearing conditions (Wilson et al. 1979). Mithraculus forceps is said to have facultative lecithotroph larvae, which can also ingest prey when available. It also has been found that late megalopa starvation has no significant influence on the survival to juvenile or larval duration and that temperature is the most important factor regulating survival and growth of larvae and juveniles in laboratory conditions (Figueiredo et al. 2008). However, observations by W. Santana (pers. com.) stand in contradiction to the results derived by Figueiredo’s et al. (2008) observations, as all non feeded larval stages of M. forceps reared in laboratory conditions by Santana tended to die faster and in more quantity than the fed larvae. If the facultative lecithotrophic development is confirmed for M. forceps, it might help to explain (along with constant larval supply) the ability of the widely distributed M. forceps to colonize new areas offshore. Mithrax forceps is a popular species in the aquarium trade and may come under pressure from the pet trade in the future (Penha-Lopes et al. 2006; Figueiredo et al. 2008).
Remarks. Mithraculus forceps can co-occur with Teleophrys pococki and very small juveniles of the two species can be mistaken for each other at a first glance. However, those of M. forceps can be easily recognized by having the carapace more flattened and grooved and the cheliped carpus with acute spines — cheliped carpus with only a tubercle of variable size near the inner anterolateral angle in aged specimens (Fig. 21A–D) (vs carapace markedly swollen, particularly at the branchial, cardiac and intestinal regions, and cheliped carpus devoid of acute spines in T. pococki) (Fig. 24A–G).
The carapace becomes distinctly wider than long with growth in males and females of M. forceps. The pereopods P2–P5 have many stiff setae and are spiny in developing specimens (denticulate in aged ones), which favor the adherence of fouling organisms (Fig. 21A–D). The ejaculatory canal aperture of the first gonopod is not fully formed until the males attain 8.8 m (cw) (Mollemberg et al. 2021). The carapace and chelipeds are glabrous and practically never have fouling organisms adhered to it (Fig. 21A, C).
In the specimens from the São Pedro and São Paulo Archipelago the dorsal surface of the carapace looks more polished and the carapace grooves more faint.
A. Milne-Edwards (1875: pl. 23, fig. 1) depicted the holotype male (cw 35 mm) of M. forceps and stated that it was from Cayenne. Therefore, its type locality can be narrowed down to Cayenne, French Guiana.