Planes marinus Rathbun 1914

Planes marinus Rathbun, 1914

(Fig. 51A, B)

Planes marinus Rathbun, 1914: 120 [Type locality: Lower California, 23°49’N, 12°750’W].

Trindade specimens. 1 juvenile female (MZUSP 40330), 1 juvenile (MZUSP 40240), Trindade Island, Praia da Calheta, 20°30’28.89’’S, 29°18’37.76”W, J.B. Mendonça coll., 11.xii.2017, on washed log, low tide.

Size of largest female (juvenile): cl 7 mm, cw 8 mm.

Comparative material examined. Planes marinus: United States: 2 males, 1 female (USNM 88069), Oregon, Lincoln Beach, 29.xii.1947, from Japanese mine [F.A. Chace det.]. Brazil: São Paulo: 3 ovigerous females (MZUSP 2112), Alcatraz Island, Instituto de Pesca coll., v.1965. Rio Grande do Sul: 1 ovigerous female (MZUSP 13285), Praia do Cassino, Rio Grande, A. Santos coll., 18.ii.2000.

Distribution. Brasil (São Paulo, Santa Catarina, Rio Grande do Sul) (Prado & Melo 2002), Argentina (Mar Chiquita) (Spivak & Bas 1999). This is the first record of P. marinus from Trindade. Central Atlantic: Saint Helena (Chace 1966), Trintan da Cunha (Holthuis & Sivertsen 1967). Eastern Pacific: from Canada to Mexico (Lower California) and Chile (Valdivia, Atacama Trench) (Chace 1951). Central Pacific and South China Sea: Japan, China (Xisha Island), Hawaii, New Zealand (including Kermadec Islands) (Kepel et al. 2002 and references therein).

Ecological notes. Little is known about the biology of Planes marinus. This is an epipelagic species associated with drifting flotsam, sometimes syntopically with other invertebrates (e.g. Caprella andreae Mayer, Lepas anatifera Linnaeus, Mytilus galloprovincialis Lamarck, Plagusia depressa, and Planes minutus), and as epibiont of the sea turtle Lepidochelys olivacea (Eschscholtz) (Spivak & Bas 1999; Kepel et al. 2002; Frick et al. 2011; Pinheiro et al. 2013). Prevalence of limb autotomy can be high (Spivak & Bas 1999), likely as a result of agonistic interactions (Frick et al. 2011). Adults occur in heterosexual pairs, ovigerous females carry between 5,000 and 20,000 eggs, and megalopae can recruit to host turtles (Spivak & Bas 1999; Frick et al. 2011). The diet of P. marinus collected from the sea turtle L. olivacea from the eastern tropic Pacific and the Hawaiian islands included Planes and Plagusia megalopae, Pleuroncodes planipes Stimpson, ciprid larvae and cirri of cirripeds, cnidarian, salps, and unidentified animal and plant material. Apparently, P. marinus consumes less animal materials and more plant materials than P. minutus (Frick et al. 2011, P. minutus as P. major).

Remarks. Among the specimens examined by Spivak & Bas (1999) from Argentina, 3 males and 3 females had a large white spot that covered most of the anterior half of the carapace similar to that of the juvenile female MZUSP 40330 from Trindade (Fig. 51A).

Planes marinus and P. minutus (Fig. 51A–D) have both been recorded from Trindade (this report) and St. Helena, while neither of the two species were recorded from the Ascension Island to date (Chace 1966; Manning & Chace 1990; De Grave et al. 2017).

The specimens from Brazil previously identified by Prado & Melo (2002) with P. marinus were reassessed and their identity is here confirmed as P. marinus (see above under comparative material). The main morphological differences between Planes marinus and P. minutus are briefly discussed below under P. minutus.