Pinnotherinae De Haan, 1833

Subfamily Pinnotherinae De Haan, 1833 View in CoL

Genus and sp. indet.

Fig. 1 View Fig

Material and measurements: one poorly preserved carapace, slightly compressed transversally (MSNM i29211 – lcxp: 5 mm; wcxp: 5 mm).

pea crabs, mainly living commensally with shells, tests, on tubes of bivalve mollusks, ascidians, holothurians and polichaete worms ( Davie, 2002). Two extant species have been recognized and widely accepted from the Mediterranean Sea, including the Northern Adriatic Sea ( Becker & Turkay, 2010: 1556), Nepinnotheres pinnotheres (Linnaeus, 1758) and Pinnotheres pisum (Linnaeus, 1767), mainly infesting selected species of bivalves. Both show generic affinities with the smooth carapace shape of the studied specimen, but differing mainly in the absence of the transverse short groove and the bilobate front in N. pinnotheres . Unfortunately, no fossil records of the subfamily have been recorded from the Pliocene Mediterranean area to date.

This record, the first for a representative of the pin- notherid pea crabs from the Pliocene of the Italian paleo Mediterranean area, considerably increases the sparse knowledge about the fossil distribution of the family.

Description. Smooth subtrapezoidal carapace, as long as wide; carapace convex dorsally, more inflated posteriorly; shoulders of carapace rounded; straight narrow front weakly produced medially; orbits?very small, poorly preserved; anterolateral margins slightly converging frontally, posterolateral margins short, diverging posteriorly, with a rounded concave indentation at level of the P5 insertion; posterior margin nearly straight; carapace regions undefined, but with a short transverse gastro-car- diac groove.

Discussion. Davie (2002) provided the following diagnosis for the Pinnotheridae De Haan, 1833 , briefly describing the carapace characters: “ Carapace typically more or less round or transversally oval often poorly calcified especially in commensal females; anterolateral margins smooth or minutely toothed; front narrow, orbits and eyes very small.” Though the present list includes some ambiguous genera into Pinnotherinae De Haan, 1833 (see Ng et al 2008: 253; Palacios Theil et al. 2016, for full discussion), Sakai (1976) provided a diagnosis for the subfamily mainly based on the pleonal appendages, not typically useful in fossil comparisons, reporting the carapace simply as “not appreciably broader than long, typically more or less circular and rounded”.

Though the studied specimen does not preserve the pleonal appendages, some dorsal characters, such as the small size and typical subrounded shape of the smooth carapace, more inflated posteriorly, short straight front poorly produced medially, and?very small orbits, support its assignment tentatively to the Pinnotherinae De Haan, 1833 . Unfortunately, the absence of other important diagnostic distinctive characters of the cephalic and pleonal appendages does not allow us to make a closer systematic assignation.

Pinnotherinae View in CoL includes several extant and fossil genera (see Ng et al., 2008: 248-251) of small, endosymbiotic