Alpioniscus thanit, Taiti & Argano, 2009

Taiti, Stefano & Argano, Roberto, 2009, New species of terrestrial isopods (Isopoda: Oniscidea) from Sardinia *, Zootaxa 2318, pp. 38-55 : 39-44

Alpioniscus thanit sp. nov.

( Figs 1–3)

Type material. Holotype ♂: NU, Dorgali, Cala Fuili, 40°15’27.8”N - 9°36’56.2”E ( WGS84 ), 25.IV.2008, leg. R. Argano and S. Taiti ( MZUF 9281 ).

Paratypes: 13 ♂, 29 ♀♀, NU , Dorgali, Cala Fuili, 40°15’27.8”N - 9°36’56.2”E ( WGS84 ), 25.IV.2008, leg. R . Argano and S. Taiti ( MZUF 9281 ) ; 1 ♂, same locality, 19. V .2004, leg. S. Cianfanelli and E. Talenti ( MZUF 9282 ) ; 1 ♂, 3 ♀♀, 1 juv., NU , Galtellì, Monte Tuttavista, Pozzo 1 Tres Puntas, 19.III.2008, leg. P. Marcia ( MZUF 9283 ) .

Diagnosis. A species of Alpioniscus characterized by antennal flagellum of eight articles, antennula with up to 10 aesthetascs, male pereopod 7 merus with a large rounded basal lobe bearing three setose teeth, male pleopod 1 exopod with a long and narrow posterior point and sinuous outer margin, and male pleopod 2 endopod of three articles with a short bifid terminal seta.

Description. Maximum length: ♂, 5.5 mm; ♀, 6.2 mm. Colourless body, pereon with almost parallel sides, pleon narrower than pereon. Back strongly granulated; disposition of granules as in Fig. 1A; each granule with an ovoid scale-seta at the top ( Fig. 1B). Numerous gland pores on lateral margins of pleonites 4 and 5, telson and uropodal protopods; some gland pores on dorsal surface of uropodal protopod and exopod. Eyes absent. Cephalon ( Fig. 1C–E) with suprantennal line bent downwards, clearly visible only at sides; antennal lobes quadrangular with a central depression. Posterior margin of pereonite 1 convex, of pereonites 2, 3 straight, and of pereonites 4–7 progressively more concave ( Fig. 1A). Pleonites 3–5 with no posterior points visible in dorsal view ( Fig. 1F). Distal part of telson with concave sides and broadly rounded apex ( Fig. 1F). Antennula ( Fig. 1G) of three articles; distal article longer than second and first, flattened and bearing 9 or 10 aesthetascs on apical margin. Antenna ( Fig. 1H) with peduncle strongly granulated; fifth article as long as flagellum; flagellum of eight articles with one row of aesthetascs on second, third and fifth article. Mandibles with one penicil in the right ( Fig. 2A) and three penicils in the left ( Fig. 2B). Outer branch of maxillule with 5+5 teeth, apically entire, and two slender stalks; inner branch with three penicils ( Fig. 2C). Maxilla with setose and bilobate apex, inner lobe smaller ( Fig. 2D). Maxilliped endite narrow, with a large apical penicil ( Fig. 2E). Pereopods with an ungual seta and a large, bifid and setose dactylar seta ( Fig. 3A). Uropod ( Fig. 1F) with protopod slightly grooved on outer margin; endopod distinctly shorter than exopod, more proximally inserted.

Male: Pereopod 1–4 ( Fig. 3A) with carpus and merus bearing numerous short scales on sternal margin. Pereopod 7 ( Fig. 3B–C) ischium with straight sternal margin; merus with concave sternal margin and a large rounded lobe in the proximal part bearing three setose teeth. Genital papilla ( Fig. 3D) with a spatuliform apical part. Pleopod 1 ( Fig. 3D) exopod with a very long narrow posterior point and deeply sinuous outer margin; endopod narrow with almost parallel sides and with enlarged basal part, armed with a long apical seta. Pleopod 2 ( Fig. 3E) exopod triangular with convex outer margin; endopod of three articles, slightly longer than exopod, third segment about three times shorter than second with a strong bifid terminal seta.

Etymology. The new species is named after Thanit, divinity of earth and fertility in the mysterious pantheon of the Nuragic culture.

Remarks. At present the genus Alpioniscus includes 27 species ( Schmalfuss 2003) subdivided into two subgenera: Alpioniscus Racovitza, 1908 with 12 species, and Illyrionethes Verhoeff, 1927 . According to Tabacaru (1996) the two subgenera can be distinguished solely on the different relative length of the second and third article of the male pleopod 2 endopod: in Alpioniscus the second article is shorter or equal to the third, while in Illyrionethes it is distinctly longer. It is difficult to judge whether this difference can be enough to distinguish two subgenera, and their validity needs to be confirmed, since also their distributions are not congruent.

According to these definitions, Alpioniscus thanit belongs to the subgenus Illyrionethes and shows its closest affinities with A. fragilis ( Budde-Lund, 1885) , endemic to Sardinia where it populates many caves ( Argano & Rampini 1973; Puddu & Pirodda 1974). The main characters of A. fragilis are here illustrated ( Figs 4 and 5) on the basis of specimens from Nurra de Sas Palumbas Cave (2 ♂, 3 ♀♀, NU, Oliena, M. Corvasi, Grotta Nurra de Sas Palumbas, 22.VII.1989, leg. S. Vanni and A. Nistri). The new species differs from A. fragilis in narrower body shape, antennula with thicker and less numerous apical aesthetascs (compare Figs 1G and 4C), male pereopod 7 with sternal margin of merus concave instead of straight (compare Figs 3B–C and 5A), male pleopod 1 exopod with outer margin distinctly sinuous instead of almost straight (compare Figs 3D and 5B), and male pleopod 2 endopod lacking the rounded lobe in the apical part of the third article (compare Figs 3E and 5C).

While all the other species of Alpioniscus are troglobitic, A. thanit seems to be an endogean species. In Cala Fuili it was collected by digging in the ground at the base of the limestone formation, from a few metres from the sea to a few hundred metres inland.