Stenasellus Dollfus, 1897

Khalaji-Pirbalouty, Valiallah, Fatemi, Yaser, Malek-Hosseini, Mohammad Javad & Kuntner, Matjaz, 2018, A new species of Stenasellus Dollfus, 1897 from Iran, with a key to the western Asian species (Crustacea, Isopoda, Stenasellidae), ZooKeys 766, pp. 39-50 : 39-40

Genus Stenasellus Dollfus, 1897

Stenasellus Dollfus, 1897:130; Racovitza 1924: 81; Birstein and Starostin 1949: 691; Magniez 1966: 177; Magniez 1968: 363; Magniez 1991: 99; Messana 1999: 1; Magniez and Stock 2000: 164.

Type species.

Stenasellus virei Dollfus, 1897, by monotypy.

Diagnosis.

Diagnoses to the genus can be found in Dollfus (1897) and Magniez (1966). The generic diagnosis presented here is more detailed than has been previously presented: Body lateral margins parallel and setose; pereonite VII longest; the antennal peduncle is 6-articulate, article VI longest, approximately 1.6 times the article V. Left mandible with incisor and lacinia mobilis bearing four cusps. Pereopod I with triangular carpus, dactylus elongated, an inferior margin with a row of contiguous scale-like flattened setae. Pereopods II-VII with an oval basis bearing some long distally plumose setae on the superior margin; dactylus shorter than elongated main unguis, bearing two secondary unguis. Pleopod I uniramous, protopod mesial margin with a simple RS or a single coupling hook, exopod elongated, mesial margin with a row distally plumose setae, distal margin fringed with a row of tiny simple short setae. Pleopod II exopod 2-articulate, article I short and without setae, article II longer than I, oval or round.

Remarks.

The first restrictive diagnosis to the genus was given by Dollfus (1897) when describing Stenasellus virei from the subterranean waters of France. Later, Magniez (1966) wrote a more detailed diagnosis, when comparing stenasellids of Africa. Subsequently, Magniez (1999) divided species of the genus Stenasellus of the Iberian Peninsula in two species groups: ( S. breuili group and S. virei group). The species of S. breuili group being recognized by protopod of the male pleopod I with a single simple seta; pleopod II appendix masculina with cylindroid and elongated distal article, little or no twisted, bearing short setae (spine) on apical margin; and pleopods IV and V with endopod smaller than exopod with round apical margin. The species and subspecies that compose S. virei group stand out by the protopod of the male pleopod I with a single coupling hook on mesial margin, pleopod II appendix masculina fusiform distal article, more or less twisted, without apical short setae (spine); the exopods of pleopod IV and V, initially lamellar and broad subequal to apically rounded endopods.

In this work, two other groups of the genus Stenasellus are proposed: the first group that has pleopod III–V with entirely bilobed endopod are from western and south-eastern Asia: S. bedosae Magniez, 1991 and S. brignolii Pesce & Argano, 1981 (Thailand); S. chapmani Magniez, 1982 (Malaysia); S. covillae Magniez, 1987, S. stocki Magniez, 2001 and S. strinatii Magniez, 1991 (Sumatra); S. grafi Magniez & Stock, 2000; S. henryi Magniez & Stock, 2000 and S. messanai Magniez & Stock, 2000 (Oman). The species of the second group have pleopod II appendix masculina with slender, elongated, and tapering to an acute apex distal article and pleopod III–V with distally bilobed endopod. Except S. cambodianus Boutin & Magniez, 1985 from Cambodia, the remaining species of the second group are distributed in eastern Africa and western Asia: S. kenyensis Magniez, 1975 (Kenya), S. costai Lanza, Chelazzi & Messana, 1970 and S. migiurtinicus Messana, Chelazzi & Lanza, 1974 ( Solalia ); S. vermeuleni Magniez & Stock, 2000 (Oman), S. tashanicus sp. n. (Iran).

Based on descriptions and illustrations of the nominal species, there are some variations between the included species. The main variation is the shape of the pleopods I–V. The exopod of pleopod 1 is elongated and the medial margin of its protopod has a single coupling hook in most species (e.g., S. virei Dollfus, 1897; S. strinatii Magniez, 1991; S. vermeuleni Magniez & Stock, 2000), while some species have a pleopod 1 with short exopod and without any coupling hook (e.g., S. grafi Magniez & Stock, 2000; S. stocki Magniez, 2001). The second article of the pleopod II is round and possesses less than five marginal setae in some species (e.g., S. henryi Magniez & Stock, 2000; S. grafi Magniez & Stock, 2000; S. nuragicus Argano, 1968), whereas some species have an oval and elongated second article with more than 10 marginal setae (e.g., S. vermeuleni Magniez & Stock, 2000; S. buili Remy, 1949; S. kenyensis Magniez, 1975). Moreover, the endopod of pleopods III–V has a rounded distal margin (e.g., S. virei Dollfus, 1897; S. asiaticus Birstein & Starostin, 1949; S. buili Remy, 1949), some species have distally bifurcated endopod (e.g., S. ruffoi Messana, 1993; S. vermeuleni Magniez & Stock, 2000; S. kenyensis Magniez, 1975) and in some species the endopod is deeply bilobed (e.g., S. javanicus Magniez & Rahmadi, 2006; S. grafi Magniez & Stock, 2000; S. henryi Magniez & Stock, 2000). In addition, the medial margin of their maxilliped endite differs in having a different number of coupling hooks (2-6).