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

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Stenasellus Dollfus, 1897


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.


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.


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).