Amphithrax hemphilli

Amphithrax hemphilli (Rathbun, 1892)

(Figs. 19A–I, 20A, B)

Mithrax hemphilli Rathbun, 1892: 263 [Type locality: Indian Key, Florida].

Trindade and Martin Vaz specimens. 1 male (MZUSP 40714), 1 female (MZUSP 39862), Trindade Island, Enseada dos Portugueses, Farol, 20º29’52.3’’S, 29º19’15.6”W, J.B. Mendonça coll., 17.iv.2014, 12.9 m. 1 juvenile male (MZUSP 40790), 23.x.2014, 12.5 m, on Favia sp. 1 male (MZUSP 40135), ibidem, POIT, from the stomach of a spotted grouper fished at night, C.H. Guimarães coll. 24.i.2012. 1 ovigerous female (MZUSP 39852), ibidem, Ponta da Calheta, 20º30’18.72’’S, 29º18’31.67”W, J.B. Mendonça coll., 05.xi.2014, 13.9 m. 1 juvenile male (MZUSP 33736), ibidem, 20º30’18.72’’S, 29º18’31.67”W, J.B. Mendonça coll., 11.xi.2014, 16 m. 1 male (MZUSP 33735), 1 juvenile female (MZUSP 39907), ibidem, 20.x.2014, 17 m. 1 juvenile female (MZUSP 40583), ibidem, Enseada das Orelhas, 20º29’40.2’’S, 29º20’32.9”W, J.B. Mendonça coll., 24.vii.2018, 11.3 m. 1 juvenile male (MZUSP 39838), 1 juvenile (MZUSP 39846), ibidem, 1.vii.2016, 9.2 m. 1 juvenile female (MZUSP 39832), ibidem, 21.vii.2015, associated with calcareous sponge, 15 m. 1 male (MZUSP 40600), ibidem, Ilha da Racha, 20º30’26.5’’S, 29º20’48.0”W, J.B. Mendonça coll., 30.vii.2018, 23 m. 1 juvenile (MZUSP 39916), ibidem, 1.vii.2016, 21.4 m. 1 juvenile female (MZUSP 39837), ibidem, 1.vii.2016, 21.4 m. 1 juvenile (MZUSP 33821), ibidem, Ponta da Cachoeira, 20º30’31.18’’S, 29º20’39.59”W, J.B. Mendonça coll., 21.vii.2015, 19 m. 1 male, 2 juvenile females (MZUSP 40665), 2 ovigerous females (MZUSP 40728), ibidem, Enseada da Cahoeira, Farrilhões, 20º31’29.6’’S, 29º19’52.0”W, J.B. Mendonça coll., 8.vii.2013, 9.5 m. 1 male (MZUSP 39677), ibidem, 20º31’22.4’’S, 29º19’52.0”W, J.B. Mendonça coll., 22.vii.2015, 22.6 m. 1 juvenile female (MZUSP 41133), Martin Vaz Archipelago, 20º28’38.61’’S, 28º51’14.66”W, J.B. Mendonça coll., 25.i.2019, 13.1 m. 1 male (MZUSP 40198), ibidem, 20º28’11.51’’S, 28º51’25.01”W, J.B. Mendonça coll., 25.i.2019, 19.1 m. 1 female (MZUSP 40721), ibidem, 20º28’38.61’’S, 28º51’14.66”W, J.B. Mendonça coll., 25.i.2019, 13.1 m.

Size of largest male: cl 32 mm, cw 34 mm; largest female: cl 32 mm, cw 36 mm.

Comparative material examined. United States: holotype, immature female (USNM 15823), Florida, Indian Key, no further details. Brazil: Pernambuco: 1 male, 2 ovigerous females, 1 juvenile female (MZUSP 8328), Fernando de Noronha Archipelago, Ilha de Lucena, Buraco do Inferno, P.S. Young coll., 3.vii.1986. Bahia: 3 males, 1 female (MZUSP 28077), Ilha de Boipeba, Praia de Bainema, stn 1, 13º37.807’S, 38º53.625’W, M. Tavares coll., 15.ix.2012, intertidal. Espírito Santo: 1 male (MZUSP 18003), 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.

Distribution. Florida, Antilles, Caribbean coast of Colombia Venezuela and Brazil (Maranhão all way south to Rio de Janeiro) (Vélez 1978; Wagner 1990; Melo 1996; Cruz Castaño & Campos 2003; Assugeni et al. 2017). Brazilian oceanic islands: Rocas Atoll (Paiva et al. 2007 and references therein). This is the first record of A. hemphilli from Fernando de Noronha, the Vitória–Trindade Seamount Chain (Dogaressa Bank) and Trindade and Martin Vaz. Amphithrax hemphilli has also been reported from the Pleistocene of Barbados (Klompmaker et al. 2015).

Ecological notes. Amphithrax hemphilli is a rather common species in hard-bottom communities in northeastern Brazil and yet very little is known about its ecology. It has been reported from the tide mark down to 60 m inhabiting coralline and stone reefs, sand reefs of Phragmatopoma caudata, calcareous algae, dead corals, but also coral rubble, limestone debris, and even Thalassia beds on the Caribbean coast of Colombia (Vélez 1978; Wagner 1990; Melo 1996; Felder et al. 2009; Santos et al. 2012; Giraldes et al. 2015; Lane-Medeiros et al. 2021). In Trindade we found a juvenile female associating with a calcareous sponge and the scleractinian coral Favia sp. Juveniles and adults were commonly found with bits of sponges and organic debris mixed with fragments of minerals attached to the carapace and walking legs P2–P5 (Fig. 19A, E), some juveniles were heavily decorated with sponges. Seemingly, the decorating behavior change with ontogeny in A. hemphilli (see Hein & Jacobs 2016 about the spider crab Oregonia gracilis). Freitas et al. (2017) showed that the red grouper Epinephelus morio (Valenciennes) feeds heavily on crustaceans, including A. hemphilli. In Trindade, a large specimen (MZUSP 40135) was recovered from the stomach of a spotted grouper. In the Caribbean, Octopus vulgaris Cuvier preys upon a variety of invertebrates, including A. hemphilli (see Anderson et al. 2008).

Remarks. The shape, tuberculation and sharpness of the spines of the carapace vary considerably in A. hemphilli (Figs. 19A–I, 20A, B). In some specimens the carapace tubercles are clustered into strong granular humps and the carapace anterolateral spines are distinctly blunt, such as in the female USNM 21948 from coastal Bahia, Brazil (Rathbun 1925: pl. 139, fig. 2), and in the males and females MZUSP 28077 also from coastal Bahia. The Trindade and Martin Vaz specimens vary in a similar way, although less prominently. In the male MZUSP 40714, for instance, tubercles are arranged into humps and the anterolateral spines are less blunt. However, the male MZUSP 40135 has strong carapace humps. The proportions and spinulation of the carapace vary with growth and development (see also Vélez 1978). Juvenile and immature specimens are usually much longer than wide and the ornamentation of the carapace is very dissimilar from that of full-grown specimens. Juveniles and immatures have much longer and sharp spines, which additionally are provided with spinules in the juveniles. The orbital spines are long and sharp in juveniles, but short and blunt with age (Figs. 19A–I, 20A, B).

The roughness (stony aspect) of the body, chelipeds and walking legs enhance crypticity by matching the background. Only the cheliped propodus and fingers are smooth and the propodus is also slightly compressed laterally, so that the propodus and fingers fit closely between the smooth ventral surface of the body and the substratum and are, therefore, concealed when the cheliped is folded beneath the body.