Tethygonium, Just, Jean & Wilson, George D. F., 2007

Just, Jean & Wilson, George D. F., 2007, Revision of Austrosignum Hodgson and Munnogonium George & Strömberg (Paramunnidae) with descriptions of eight new genera and two new species, (Crustacea: Isopoda: Asellota), Zootaxa 1515, pp. 1-29 : 23

Tethygonium gen. nov.

Type species. Tethygonium quadricuspis sp. nov. —Here designated.

Species included. Tethygonium adenensis ( Müller, 1991) , comb. nov., T. armigerum ( Shimomura & Mawatari, 2000) , comb. nov., T. quadricuspis sp. nov., T. variabile ( Schiecke & Modigh-Tota, 1976) , comb. nov.

Diagnosis. Body ovate. Head front margin evenly convex, not projecting. Pereonites dorsally smooth. Pleotelson lateral margins denticulate. Eyestalks variable, vestigial to approximately twice as long as wide. Antennula article 1 at least twice length of eyestalk. Antenna article 3 with mediodistal spine. Mandible palp absent. Pereopod I carpus oval, with several (3–5) curved robust setae; propodus with simple setae only on posterior margin; dactylus posterior margin with acute spine proximal to accessory claw. Pereopod II carpus and propodus posterior margin with a few short robust setae. Uropod with 1 or 2 rami, endopod straight, apex truncate.

Remarks. The species referred here to Tethygonium present considerable variation. The type species T. quadricuspis has projections on the lateral margins of pereonites 1–4, and coxae 1–4 are not visible in dorsal view (projections only on coxae, coxae 1–4 visible in dorsal view). Eyestalks in T. adenensis and T. armigerum are 1.5 to 2.0 times longer than broad (vestigial in T. variabile and T. quadricuspis ). Tethygonium adenensis and T. armigerum are described as having uniramous uropods (biramous in T. variabile and T. quadricuspis ). We are uncertain about the significance of these differences. We prefer, for the time being, to keep the 4 species together in the new genus Tethygonium based primarily on the unusual curved carpal setae and the joint possession of an acute spine posterior to the accessory claw on the dactylus of pereopod I. These are also the principal characters by which Tethygonium differs from Boreosignum .

Distribution. Mediterranean, Gulf of Aden, Sea of Japan, southeastern Australia. 70–1000 m.