Stenasellus tashanicus, Khalaji-Pirbalouty, Valiallah, Fatemi, Yaser, Malek-Hosseini, Mohammad Javad & Kuntner, Matjaz, 2018

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 : 40-45

Stenasellus tashanicus sp. n. Figs 2, 3, 4

Material examined.

All material from Iran with locality data as follows.

Holotype. ♂ (17.5 mm), Tashan Cave, Sarjooshar Village, Tashan City, Behbahan County, Khuzestan Province, Iran, 13 August 2016, 30°51'54"N, 50°10'29"E (altitude 559 m a.s.l.), coll. Fatemi, Y. (ZMSU 2010).

Paratypes. 3 ♂♂ (17.1, 12.5, 12 mm), 2 ♀♀ (20, 11mm); 2 juveniles (7.3, 8.5 mm), same data as holotype (ZMSU 2011). 1 ♂ (15 mm), 1 ♀ (18 mm); 1 juveniles (5.5 mm), Tashan Cave, Sarjooshar Village, Tashan City, Behbahan County, Khuzestan Province, Iran, 27 August 2016, 30°51'54"N, 50°10'29"E (altitude 559 m a.s.l.), coll. Fatemi, Y. and Malek-Hosseini, M.J. (ZMSU 2012).

Diagnosis.

Body dorsal surface smooth, with scattered marginal setae. Antenna reaching to pereonite V posterior margin in male specimen, with a squama bearing three simple setae on the outer margin of the third article. Maxilla lateral and middle endites each bearing 11 curved pectinate RS; mesial margin of maxilliped endite with six coupling hooks. Appendix masculina slender, elongated, tapering to a curved acute apex; endopod of pleopods III–V distally bifurcated.

Description of male.

Body completely coral pink in the live specimen (Fig. 1C, D), length 4.2 as greatest width, head trapezoidal, with slightly concave frontal margin, dorsal surface smooth. Pereonites II–IV subequal in length, with rounded lateral margins, pereonites V–VII with posterolateral margins projected posteriorly, pereonites VI and VII sub-equal, longest (Fig. 2A, D). Pleonites I–II subequal in length, with projected posterolateral corner.

Pleotelson elongated, 1.4 as long as broad, posterior margin with two slight excavations; with scattered marginal setae.

Antennula (Fig. 3A) short, reaching pereonite I posterior margin, slightly longer than the peduncle of antenna, flagellum with 18 articles, articles 8-18 each bearing a single aesthetasc.

Antenna (Fig. 3B) peduncle articles I and II reduced; the four others longer, increasing in length from the fourth to the sixth; article VI about 1.6 times as article V, with long simple setae distally; article III with minute squama bearing two long RS, flagellum reaching to pereonite V posterior margin, up to 86 articles.

Left mandible (Fig. 3D, E) incisor and lacinia mobilis with four cusps, spine row of 18 serrate spines, molar with a row of long, tiny, simple setae. Palp article II longer than I, articles III distolateral margins with approximately 15 pectinated setae.

Maxillula (Fig. 3F) lateral endite apical margin with 12 serrate RS and eight tiny serrated smaller setae; mesial endite with three long, robust, comb and two short simple setae.

Maxilla (Fig. 3G) lateral and middle endites each with 11 curved pectinate RS; mesial endite with several rarely plumose, long robust combs, and slender simple setae.

Maxilliped (Fig. 3H) endite mesial margin with six coupling hooks, distal margin with approximately 10 serrated and rarely plumose RS; palp article I with single RS on the inferior margin, palp articles II–V with several long simple setae on the inferior margin.

Pereopod I (Fig. 3I) basis length 1.66 width, ischium superior margin with one RS on distal corner and five small RS on the medial projection; merus supradistal angle with three RS; carpus triangular, inferior margin covered with several long and short simple RS; propodus inferior margin covered with several long simple RS set in amongst some serrated RS; dactylus 9.2 times as long as basal width, inferior margin with a row of contiguous scale-like flattened setae with accessory setulae, main unguis elongate.

Pereopod II (Fig. 3J) basis about 1.8 times as long as the greatest width, superior margin with nine long distally plumose setae; ischium superior margin with five long RS; merus supradistal angle with two long RS, inferior margin with nine long simple setae; carpus superior margin with five simple setae, inferior margin covered with several long and short simple RS; propodus inferior margin covered with several short, simple, acute setae, supradistal angle with two long simple and single sensory palmate setae; dactylus shorter than main unguis, with two secondary unguis.

Pereopod III (Fig. 4A) is similar to pereopod II as illustrated.

Pereopod VII (Fig. 4B) basis about two times as long as the greatest width, superior margin with nine long distally plumose setae; Ischium length 2.2 width; merus supradistal angle with three long RS; carpus length 5.0 width, inferior margin covered with several long and short simple RS, supradistal angle with a long simple and a single sensory palmate setae; propodus length 7.3 width, inferior and superior margins covered with several short, simple, acute setae, supradistal angle with two long simple and a single sensory palmate setae; dactylus with elongated main unguis, bearing two secondary unguis.

Penial processes (Figs 2C, 4C) elongated, cylindrical, about 5.8 times as long as the greatest width.

Pleopod I (Fig. 4D) protopod length 1.2 width, mesial margin with a single coupling hook, exopod elongated, mesial margin with a row of 21 PMS and four simple setae, apical margin with row of ~18 simple fine setae, lateral margin concave.

Pleopod II (Fig. 4E) protopod elongated, length 1.7 width, exopod article I small, without seta, article II oval, with ~ 41 PMS; endopod small, with two apical, long, simple setae; appendix masculina length 1.4 article I length, 11.4 basal length, tapering to curve acute apex.

Pleopod III (Fig. 4F) exopod with transverse suture, apical margin with ten slender simple setae; endopod 0.6 as long as exopod, bifurcated distally.

Pleopod IV (Fig. 4G) exopod with transverse suture, distolateral margin with 22 slender simple setae; endopod 0.8 as long as exopod, bifurcated distally.

Pleopod V (Fig. 4H) exopod and endopod subequal in length, without marginal setae.

Uropods (Fig. 4I) protopod and rami covered with scattered acute simple setae; endopod longer than exopod, both rami with distal tuft of setae.

Female.

(Fig. 2B) Typically, longer than the male, apart from sexual characteristics similar to male, pleotelson is broader and antenna is longer than male.

Etymology.

The name of this species comes from the type locality, the Tashan Cave, Iran.

Habitat.

The isopods were collected from two pools in the dark zone of the Tashan Cave (at 20 to 200 cm depths). They were observed in all life cycle stages. They were observed crawling on the floor and hiding inside the sediment and cavities of the pools, as well as swimming in the water column. Mousavi-Sabet et al. (2016) described a blind fish from this cave (see Fig. 1D).

Remarks.

Stenasellus tashanicus sp. n. can be identified by a slender and distally acute appendix masculina, and a maxilliped endite with six coupling hooks on the mesial margin. The new species is the largest known Stenasellus member: length up to 18 mm in males and 20 mm in females. The new species is similar to S. vermeuleni Magniez & Stock, 2000 (known from Wadi Halban, Oman), in having an appendix masculinum with acute apex. The shape of pleopods III–V in both species is also similar. Based on the drawings and description of S. vermeuleni , the new species differs by having a uropodal exopod smaller than the endopod (rather than subequal in length), pleopod I apical margin with a row of 18 simple fine setae (rather than six), exopodal article II of pleopod II is narrower than pleopod II in S. vermeuleni and pleopod V exopod and endopod subequal in length (rather than a smaller exopod). Based on the description and drawings of S. asiaticus by Birstein and Starostin (1949) from Turkmenistan, this species is readily distinguished from the new species by setose body dorsal surface (rather than smooth body surface) and its flattened appendix masculina (rather than a narrow with an acute apex).