Calappa granulata (Linnaeus, 1758) (Crustacea, Decapoda, Brachyura, Calappidae) and Astiplax aspera n. gen., n. sp. (Crustacea, Decapoda, Brachyura, Goneplacidae) from the Asti sands Fm. (Late Pliocene) of S. Pietro (Asti, Piedmont, NW Italy)

Calappa granulata (Linneo, 1758) (Crustacea, Decapoda, Brachyura, Calappidae) y Astiplax aspera n. gen., n. sp. (Crustacea, Decapoda, Brachyura, Goneplacidae) de la Formación Asti (Plioceno tardío) de S. Pietro (Asti, Piamonte, NW Italia)

Alessandro Garassino^1,*, Giovanni Pasini²

¹ Museo di Storia Naturale, Sezione di Paleontologia, Corso Venezia 55, 20121 Milano, Italia. *alegarassino@gmail.com

Manuscript received: July 6, 2012.
Corrected manuscript received: October 20, 2012.
Manuscript accepted: October 22, 2012.

Abstract

Two crabs from the Pliocene sands of S. Pietro (Asti, Piedmont, NW Italy) have been assigned to Calappa granulata (Linnaeus, 1758) (Calappidae De Haan, 1833) and to Astiplax aspera n. gen., n. sp. (Goneplacidae MacLeay, 1838). Although C. granulata has already been reported from the Pliocene of other Italian regions, the Piedmont specimen represents one of the most complete carapaces known to date in the fossil record of this extant species. The discovery of Astiplax n. gen., with A. aspera n. sp. increases the number of species of Goneplacidae from the Pliocene of Italy, limited to Goneplax rhomboides (Linnaeus, 1758) and G. sacci Crema, 1895.

Keywords: Crustacea, Decapoda, Brachyura, Late Pliocene, Italy.

Dos cangrejos de las areniscas del Plioceno de S. Pietro (Asti, Piemonte, NO Italia) han sido asignados a Calappa granulata (Linnaeus, 1758) (Calappidae De Haan, 1833) y a Astiplax aspera n. gen., n. sp. (Goneplacidae MacLeay, 1838). Aunque C. granulata ha sido previamente reportada del Plioceno de otras regiones de Italia, el ejemplar de Piemonte representa uno de los más completos caparazones conocidos hasta la fecha en el registro fósil de esa especie viviente. El descubrimiento de Astiplax n. gen., con A. aspera n. sp., incrementa el número de especies de Goneplacidae del Plioceno de Italia, limitado a Goneplax rhomboides (Linnaeus, 1758) y G. sacci Crema, 1895.

Palabras clave: Crustacea, Decapoda, Brachyura, Plioceno superior, Italia.

1. Introduction

The specimens were discovered in sand blocks crashed by natural erosion along the hills of S. Pietro outcrop located near Asti, Piedmont (NW Italy), in the Astian Pliocene Basin. The yellow sedimentary Asti sands constitute the main body of the surrounding hills, and were deposited in a coastal environment of the old Padano Gulf. The marine Asti sands Fm. is rich in fossils, mainly in molluscs, indicating an infralittoral environment (Astiana facies), and was dated to the Late Pliocene (Damarco, 2009). Lacking micropaleontological and sedimentological data, we assign the specimens to the Asti sands Fm. (Late Pliocene) in a generic way.

2. Material

The sample includes two specimens: one carapace dorsally preserved as a three-dimensional mould with the original epicuticle partially preserved; one three-dimensional specimen preserving the carapace and the incomplete right cheliped. The specimens have been assigned to Calappa granulata (Linnaeus, 1758) (Calappidae De Haan, 1833) and Astiplax aspera n. gen., n. sp. (Goneplacidae MacLeay, 1838). The specimens are deposited in the Palaeontological Collections of the Museo di Storia Naturale di Milano (MSNM).

The systematic arrangement used in this paper follows the recent classifications proposed by Castro (2007) and Ng et al. (2008).

lc: length of carpus; lcxp: length of carapace; lm: length of merus; wcxp: width of carapace.

3. Systematic Palaeontology

Section Eubrachyura de Saint Laurent, 1980
Superfamily Calappoidea De Haan, 1833
Family Calappidae De Haan, 1833
Genus Calappa Weber, 1795

Type species: Cancer granulatus Linnaeus, 1758, subsequent designation by Latreille (1810).

Calappa granulata (Linnaeus, 1758)
Figure 1

Cancer granulatus Linnaeus, 1758: 627.

Cancer granulatus – Linnaeus, 1767: 533.

Calappa granulata – Garassino and De Angeli, 2004: 38, fig. 4 (1-3). – Garassino et al., 2004: 264, fig. 7 a-c. – De Angeli and Garassino, 2006: 40. – Ng et al., 2008: 48. – De Angeli et al., 2009: 176, 177, 195, 196, fig. 8a, b. – Schweitzer et al., 2010: 82. – Garassino et al., 2012: 51. – Pasini and Garassino, 2013: 320, 321.

Material and measurements: one carapace in dorsal view (MSNM i27827 – lcxp: 33 mm; wcxp: 40 mm).

Discussion. The specimen has been compared with the extant species of Calappa Weber, 1795, from the Indo-West Pacific region from which it differs notably in the general shape and ornamentation of the carapace and distribution of the posterolateral teeth (Ng et al., 2008); and with the extant and fossil C. granulata, widespread in the Mediterranean Sea.

Zariquiey-Álvarez (1968) pointed out the main characters of this species, such as the convex and wider than long carapace; rounded anterolateral margins; straight posterior margin; poorly produced, bidentate straight front; small well-marked orbits, inferior margin with two small separate teeth; anterolateral margins with small poorly developed teeth wider at the base, followed on the posterior third by four larger teeth pointed medially; posterior margin straight lacking teeth on the median portion; mesogastric and cardiointestinal regions appear fused, forming a prominent longitudinal ridge delimited laterally by two marked longitudinal grooves; at each side of these two grooves, generally four longitudinal grooves not reaching the posterior margin and delimiting other ridges; all the ridges bear longitudinally nodules of decreasing size, with the larger sizes in the mesogastric region; a small nodule is present in the anterior cardiac region; the other regions are covered by granules.

The specimen, although poorly preserved, shows close affinities with C. granulata as follows: suboval convex carapace wider than long; straight front and small rounded orbits; raised convex anterolateral margins, with posterior triangular and pointed teeth and nearly straight posterior margin; regions well marked by two longitudinal grooves that divide the carapace in three parts; tuberculate longitudinal ridges and a dense granulation covering the regions, mainly the central dorsal part of the carapace. The specimen is also very similar in shape and ornamentation to the only carapace from the Italian Pliocene of Tuscany reported by De Angeli et al. (2009; 177, fig. 8). Based on these data we attest that the previous reports from the Pliocene of Piedmont, Emilia Romagna, and Sicily and from the Pleistocene of Monte Pellegrino (Sicily) can be assigned to the extant and fossil C. granulata (Ristori, 1891; Gemmellaro, 1914; Garassino and De Angeli, 2004; Garassino et al., 2004; De Angeli et al., 2009; Pasini and Garassino, 2013).

Superfamily Goneplacoidea MacLeay, 1838
Family Goneplacidae MacLeay, 1838
Subfamily Goneplacinae MacLeay, 1838
Genus Astiplax n. gen.

Diagnosis: carapace transversely rectangular, much wider than long; front slightly turned downwards, not marked by slight median notch or projection; inner edge of supraorbital margin distinct; wide orbits 1.3 longer than front; outer orbital angle without teeth or spines; supraorbital margins strongly sinuous; suborbital margins sinuous, toothless; anterolateral margins slightly convex, toothless; posterolateral margins straight, converging posteriorly; posterior margin long, slightly convex; dorsal surface of carapace conspicuously granular, with slight horizontal ridges, moderately convex, without clear indication of regions; produced lateral knock under the postorbital angles; stout and heavy chelipeds, strongly granulose.

Etymology: from Asti, city located close to the outcrop where the specimen was discovered.

Type species: Astiplax aspera n. gen., n. sp. (gender feminine).

Description: as for the type species.

Discussion. The family Goneplacidae, as reported by Castro (2007), has the following diagnostic characters: carapace transversely rectangular, subquadrate, or trapezoidal; front narrow to wide, typically lamellar, straight; dorsal surface smooth; varying number of anterolateral spines posterior to outer orbital angle (sometimes none but typically one or two); orbits moderately to conspicuously wide, long; fissure in supraorbital margin absent; dorsal surface of carapace typically smooth or with slight horizontal ridges, moderately convex, without clear indication of regions. Most of these characters are present in the specimen, here, assigned to Goneplacidae. Moreover, we justify the erection of the new genus Astiplax based on some supplementary morphological observations. The outer orbital angle and the anterolateral margin of carapace spineless of Astiplax n. gen. are two characters shared with the extant Notonyx Milne Edwards, 1873. The carapace, however, is distinctively quadrate and the typically smooth dorsal surface of Notonyx exclude Astiplax n. gen. from belonging to this genus. The dorsal surface of the carapace of the Astiplax n. gen., with slight horizontal ridges, moderately convex, without clear indication of regions, is a character shared with some species of the extant genera: Carcinoplax H. Milne Edwards, 1852, Pycnoplax Castro, 2007, Goneplax Leach, 1814, Neogoneplax Castro, 2007, Paragoneplax Castro, 2007, and Ommatocarcinus White, 1852 (see Castro, 2007). The dorsal surface of the carapace, however, conspicuously granular in Astiplax n. gen., excludes it from belonging to Pycnoplax, Goneplax, Neogoneplax, and Paragoneplax where the dorsal surface of the carapace is typically smooth. We also exclude it from belonging to Carcinoplax, although slight horizontal ridges and granules along the antero- and posterolateral margins are present in two species, C. cracens Castro, 2007, and C. tuberosa Castro, 2007; as reported by Castro (2007) these are not considered as generic characters. Finally, although the carapace of Ommatocarcinus has slight horizontal ridges, a smooth or conspicuously granular dorsal surface and the anterolateral margin toothless, the outer orbital angles, each with a conspicuous acute tooth, exclude Astiplax n. gen. from belonging to this genus.

Astiplax aspera n. sp.
Figures 2-4 (3)

Holotype: MSNM i27828 – specimen, lacking left cheliped, chela of right cheliped, and ambulatory legs (lcxp: 22 mm (excluding front); wcxp: 32 mm; lm: 20 mm; lc: 8 mm).

Type locality: S. Pietro (Asti, Piedmont, NW Italy).

Geological age: Asti sands Fm., Late Pliocene.

Description. Carapace transversely rectangular, much wider than long; widest at junction between antero- and posterolateral margins; front slightly turned downwards, not marked by slight median notch or projection; inner edge of supraorbital margin distinct; wide orbits 1.3 longer than front, with granular eye-stalk; orbits greatly expanded distally with outer orbital angle toothless; supraorbital margins strongly sinuous, without fissures; sinuous, toothless suborbital margins; toothless anterolateral margins slightly convex; long, straight posterolateral margins, converging posteriorly; long posterior margin slightly convex; deep gastric pits; branchiocardiac grooves slightly distinct in cardiac region; dorsal surface of the carapace strongly granular, with bigger granules in the metagastric region; slight horizontal ridges, moderately convex, without clear indication of regions; an elevated notch under both postorbital angles, produced forwardly. Stout, heavy cheliped, with moderately long merus, subtriangular in section; carpus subsquare in section, dorsolaterally convex and toothless; merus and carpus surface strongly granular; granules of cheliped bigger than those of the carapace.

Discussion. Among the fossil crabs from the Pliocene of Italy, only Simonellia quiricensis Vinassa de Regny, 1897 (Euryplacidae Stimpson, 1871) from S. Quirico d'Orcia (Tuscany) could be compared with the new genus (Vinassa de Regny, 1897). As reported by De Angeli and Garassino (2006), however, the holotype of this species is lost, making difficult a comparison between the two species based on the published description and the line drawing (Vinassa de Regny, 1897: Pl. 2, figs. 1, 1a). Moreover, this specimen was reported from the clays of S. Quirico d'Orcia (middle Pliocene), younger than the Asti sands Fm. (Late Pliocene) from where the specimen was discovered. Simonellia quiricensis is therefore considered a nomen dubium for not having other specimens of the same species and from the same locality in order to be able to confirm its description. Some characters, reported by Vinassa de Regny, however, distinguish Simonellia from Astiplax n. gen.: the compressed, ovoid carapace, with sharp margins; the small, ovoid orbits; the anterolateral margin with one spine. Finally it is difficult to compare the ornamentation of the dorsal surface of the carapace. Indeed the author described a "scabrous" surface, a term that does not explain if the surface is granular, tubercular or uneven.

Acknowledgments

We wish to thank P. Frediani (Gruppo Paleontologico "C. De Giuli", Castelfiorentino (Firenze), for useful information on the outcrop, and P. Castro (Biological Sciences Department, California State Polytechnic University, Pomona, USA) for useful suggestions about the systematics of Goneplacidae, careful review and criticism.

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