Plagusia depressa

Plagusia depressa (Fabricius, 1775)

(Figs. 53A–C, E, F)

Cancer depressus Fabricius, 1775: 406.

Trindade specimens. 1 male (MZUSP 41246), Trindade Island, A. Za and F. Lauria coll., 8.viii.1986, rocky coast. 1 male, 4 females (3 ovigerous) (MZUSP 41245), ibidem, Praia da Calheta, Praia da Calheta, 20°30’29.5’’S, 29°18’37.0”W, J.B. Mendonça coll., 11.vii.2015, low tide, breaking wave zone. 3 males (MZUSP 41244), ibidem, J.B. Mendonça coll., 21.vi.2016, 12.5m. 1 male (MZUSP 40327), ibidem, J.B. Mendonça coll. 20.xi.2017, low tide, breaking wave zone. 1 male (MZUSP 41247), 1 juvenile male (MZUSP 40348), ibidem, between Praia dos Andradas and Tartaruga, 20°31’03.8’’S, 29°18’08.4”W, J.B. Mendonça coll., 20.iv.2014, low tide, breaking wave zone. 4 juvenile males (MZUSP 41249), ibidem, 20°29’53.9’’S, 29°19’24.1”W, J.B. Mendonça coll., 12.iv.2014, low tide, breaking wave zone. 4 juvenile males (MZUSP 41248), ibidem, Ponta Norte, Crista do Galo, 20°29’22.1’’S, 29°20’03.1”W, J.B. Mendonça coll., 16.vi.2016, rocky tide pool, 1.5 m.

Size of largest male: cl 48 mm, cw 51 mm; largest female: cl 44 mm, cw 47 mm.

Comparative material examined. Plagusia depressa: Brazil: Ceará: 1 male (MZUSP 29769), São Gonçalo do Amarante, Taíba, PROBIO Expedition, T. Lotufo coll., 13.vi.2003. Rocas Atoll: 1 male (MZUSP 12481), R.L. Moura and R.S. Rosa coll., vii.1995. Fernando de Noronha Archipelago: 1 male (MZUSP 7245), Boldró, S.A. Rodrigues coll., 27.x.1985. Bahia: 1 ovigerous female (MZUSP 3917), Arembepe, 16.xi.1971. Central Atlantic: 1 ovigerous female (MZUSP 4831), São Pedro and São Paulo Archipelago, 1146 km off the coast of northeastern Brazil, Belmont Islet, R. Haddock coll., 19.ix.1979. 1 male, 3 ovigerous females (MZUSP 41250), ibidem, 00°55’02’’S, 29°44” W, M. Tavares coll., 4–5.iii.2018, rocky tide pool. Plagusia squamosa (Herbst, 1790): Austral Islands: 1 female (MZUSP 20327), Raivavae Island, J. Poupin coll., 3.xii.1990, reef, 0.5 m, J. Poupin leg. Plagusia immaculata Lamarck, 1818: Philippines: 1 male (MZUSP 41257), Bay of Manila, Jetty of Cavite, M. de Saint Laurent coll., 18.iii.1976, M. de Saint Laurent leg.

Distribution. Amphi-Atlantic. Western Atlantic: Bermuda, North Carolina, Gulf of Mexico, Antilles, Venezuela and Brazil (Ceará to Bahia) (Rathbun 1918; Rodriguez 1980; Melo 1996; Felder et al. 2009; Almeida & Carvalho 2014; Rosa et al. 2018). Brazilian oceanic islands: São Pedro and São Paulo Archipelago, Rocas Atoll, Fernando de Noronha and Trindade (Moreira 1920; Coelho & Ramos 1972; Holthuis 1980). Central Atlantic: Ascension and St. Helena (Chace 1966; Manning & Chace 1990). Eastern Atlantic: Azores, Canary, Cape Verde and Morocco to Angola (Miers 1886; Manning & Holthuis, 1981; González 2018).

Ecological notes. Plagusia depressa (Fig. 53A–C, E, F) is a littoral species inhabiting the splash zone of rocky shores, sandstone reefs and rocky tide pools (Fig. 53D). It has been seen rafting on flotsam and is occasionally preyed (megalopa and adults) by the sea turtle Caretta caretta (see Frick et al. 2009). Santana et al. (2019) reported that P. depressa feeds on macroalgae, gastropods, polychaetes, amphipods, decapods, tanaidaceans and ascidians. Males are usually smaller than females and also mature at smaller size. Apparently, P. depressa breeds along the year with a peak at the end of the dry season and beginning of the rainy season (April to July in northeast Brazil) (Rocha et al. 2019). Ovigerous females have been collected in September in the São Pedro and São Paulo Archipelago (Holthuis 1980), August in Trindade (this study), February in Saint Helena (Williams 1984), and May, August, September, October, and December off West Africa (Manning & Holthuis 1981). The recruitment in northeast Brazil was estimated to occur from December to March, about four months after mating (Coelho Filho et al. 2004). The larval development goes through five zoeal stages (probably six), and takes 60 days for completion under laboratory conditions (Wilson & Gore 1980). The megalopa was described by Schubart et al. (2001). Plagusia depressa is locally consumed as food in Tamandar (Pernambuco, Brazil), where it is relatively easily harvested at night using a torch and apparently is under fishing pressure (Coelho Filho et al. 2004). Dana, 1852a), and Guinusia Schubart & Cuesta, 2010 (type species: Cancer chabrus Linnaeus, 1758). The presence of flagellum on the Mxp3 exopod in Davusia and Guinusia has been used to distinguish both from Plagusia s.s., whose Mxp3 is devoid of flagellum (Guino, 2007; Schubart & Cuesta 2010). The absence of flagellum on the Mxp3 exopod has been well documented in Plagusia depressa, in which the Mxp3 exopod flagellum is already absent in the megalopa stage (Schubart & Cuesta 2010: fig. 5F). However, an aspect largely overlooked is the presence of a well-developed flagellum on the exopods of the second and first maxillipeds (Mxp2, Mxp1, respectively). The Mxp2 and Mxp1 exopods are excavated distally to receive the proximal articles of the flagella when folded (this study).

In P. depressa, the vulva is provided with a mobile operculum (Guinot et al. 2013; Guimarães et al. 2021); in the ovigerous females MZUSP 41250 the vulvae were completely obliterated by the operculae.

In the male (MZUSP 41246) the penis is completely covered and protected by the lateral expansion of the third pleonal somite (somites 3–6 fused together) and additionally is sclerotized proximally.