Platyarthrus alticolus Taiti & Checcucci, 2009

Taiti, Stefano & Checcucci, Ilaria, 2009, New species and records of terrestrial Isopoda (Crustacea, Oniscidea) from Socotra Island, Yemen, ZooKeys 31 (3), pp. 73-103 : 89-92

Platyarthrus alticolus Taiti & Checcucci , sp. n.

urn:lsid:zoobank.org:act:038A9573-9E37-462D-B357-98445905FC21

Material examined. Socotra: 1 ♀ Holotype, Hagghier Mts , Adho Dimelho, 980 m, 12°34'19.9"N 54°02'49.4"E, 22.I.2003, under stones in meadow, leg. S. Taiti, MZUF- 9227 ; 1 ♀ Paratype, same data, MZUF-9227 .

New species and records of terrestrial Isopoda (Crustacea, Oniscidea ) from Socotra Island... 91

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Diagnosis. A species of Platyarthus characterized by the dorsal ornamentation with two bosses on vertex and two prominent and two shallow ribs per side on pereionites 1–6 and two prominent ribs per side on pereionite 7, two paramedian ribs on pleonites 3–5, and very short telson with obtuse triangular distal part.

Description. Maximum length: 4.1 mm. Body very convex, colourless ( Fig. 7A, B). Dorsal ornamentation: cephalon with two paramedian large bosses on vertex; pereionites 1–6 with two more internal prominent ribs and two more external shallow ribs per side; pereionite 7 with two prominent ribs per side; pleonites 3–5 with two paramedian ribs. Dorsum with many rounded and flattened scale-setae ( Fig. 7C). Cephalon ( Fig. 7D) with median lobe broadly rounded, protruding frontwards and slightly hollow dorsally; lateral lobes subquadrangular, tranversely directed frontwards; eye absent. Pereionite 1 with posterior corners right-angled, becoming progressively more acute in the following pereionites. Pleonites 3–5 with epimera quadrangular, directed backwards. Telson ( Fig. 7E) very short, about three times as wide as long, with an obtuse triangular distal part, covering just a small part of uropodal protopods. Antenna ( Fig. 7F) with thickset peduncular articles; second flagellar article about five times as long as first. Uropods ( Fig. 7E) with thickset exopod, shorter than protopod.

Etymology. Latin alticolus = living at altitude. The name refers to the collecting site of the species at ca. 1000 m elevation on the Hagghier Mts.

Remarks. The genus Platyarthrus currently includes 28 species ( Schmalfuss 2003) mainly distributed in the Mediterranean area, with a few species from the Atlantic islands and west to Tajikistan. One species, P. acropyga Chopra, 1924 , has been described from Chilka Lake, India. In the Socotra Archipelago only the introduced species Platyarthus schoblii was previously recorded ( Taiti and Ferrara 2004).

Even if only two female specimens were collected, Platyarthrus alticolus sp. n. is worth of a description because of its peculiar dorsal ornamentation and the high probability of being authocthonous on Socotra Island. It belongs to the schoblii -group of species, characterized by the short telson and dorsal longitudinal ribs on the pereion. For the presence of four dorsal ribs per side on the pereionites 1– 6 P. alticolus is similar to P. sorrentinus Verhoeff, 1931 from southern Italy. All the other species in the group have five or six longitudinal ribs per side on pereionites 1–6. It is readily distinguishable from P. sorrentinus in having two prominent and two more shallow ribs per side instead of all with the same development, and in having two large bosses instead of ribs on the cephalic vertex (compare Pl. 8 fig. 43 in Verhoeff 1931 for P. sorrentinus ). This last character distinguishes the new species also from all the other species of the schoblii -group.