A new cave isopod species of the genus Stenasellus Dollfus, 1897 (Stenasellidae) from Iran is reported and described. The new species, Stenasellus tashanensis sp. n. was found in Tashan Cave (Khuzestan province, southwest Iran). A complete description and drawings of the new species are provided. This new species is morphologically close to S. vermeuleni Magniez & Stock, 2000 from Oman.

Isopods, Stenasellus , Stygobiont, Cavernicolous

With approximately 1.65 million km², Iran is a vast country in the Western Palearctic. Iran hosts a high variety of habitats including more than 2000 caves, mostly located in the Zagros Range (Raeisi et al. 2012). This mountain chain is rich in caves and has been the object of numerous speleological explorations dating back to the 1970’s (Juberthie et al. 2001).

In the last two decades, several studies have been conducted regarding the fauna of Iranian caves (e.g. Karaman 1998; Casale and Quéinnec 2001; Sadeghi et al. 2014; Esmaeili-Rineh et al. 2015, 2017; Malek Hosseini et al. 2016). Nonetheless, the subterranean fauna of Iran is still poorly known. Several species of oligochaetes, crustaceans (Copepoda, Isopoda, Amphipoda), hydracarids, insects, fish and amphibians, have been collected and described from Iranian caves (Juberthie et al. 2001; Esmaeili-Rineh et al. 2017; Moradmand 2017).

The family Stenasellidae, with more than 70 described species, is limited to subterranean aquatic habitats including karstic or phreatic springs (Wilson 2008). The first specimens of this family were discovered in the subterranean waters from SW France (Viré 1896). Later, Dollfus (1897) examined the specimens and described them as Stenasellus virei Dollfus, 1897. The genus Stenasellus Dollfus, 1897 has a wide distribution in the Old World from the Far East (Borneo, Cambodia, Sumatra, Thailand) to Central Asia (Turkmenistan), Arabian Peninsula (Oman, Socotra), East Africa (Kenya and Somalia), and southern Europe (Iberian Peninsula, southern France, Corsica and Sardinia) (cf. Magniez and Stock 2000).

In 1999, in a paper dealing with four new Stenasellus species from Oman, Magniez and Stock predicted the presence of Stenasellid isopods in Iran: “…we might ask if they (Stenasellidae) are present in intermediate geographical regions. Yemen, south-western Oman and southern Iran could harbour this fauna…”. In fact, by describing Stenasellus tashanensis sp. n. from Iran in the present study, their prediction has been confirmed and the antiquity and wide Tethyan distribution of the genus Stenasellus as stated by Magniez (2005, 2008), have been ratified. We collected some Stygobiont isopods from Tashan Cave (Figure 1), in southwest of Iran during a field trip on January 1, 2016, which on closer examination appeared to belong to a new species of the genus Stenasellus.

Figure 1. 

Left: Map of Iran, showing the location of Tashan Cave (black circle); Right: the type locality in Tashan Cave, with Stenasellus tashanensis sp. n.

All the specimens (two males and three females) were collected using a small hand net in Tashan cave, located 12 km north of Behbahan city in Khuzestan Province (southwest Iran). Tashan cave is located on the western side of the Zagros Mountains (Figure 1) in Neozoic limestone. Tashan Cave is about 150 m long, with two stagnant water pools which are connected to each other by small channels. The depth of the first pool, where the specimens were found, was about 1 m in the deepest part. The second pool was deeper, about 4–5 m in the deepest part. No specimen was found in the second one. The bottom of both pools is represented by greyish-white fine sediments. The pools water had the following physico-chemical characteristics: TDS = 350 mg/l, Salinity = 0.35%, Conductivity = 717 μS/cm, pH = 7.8, Temperature = 25.6 °C.

The collected specimens were preserved in ethanol 96%. One male and one female were dissected and microscopic slides of their body parts were prepared using Euparal mounting medium. To study the specimens, a stereomicroscope (Zeiss Stemi SV 11 Apo) and a compound microscope (Olympus BX 50) were used. For the chaetotaxy, Watling (1989) was followed.

The type specimens of Stenasellus species described from East Africa deposited at Zoological Museum of University of Firenze, Italy (MZF) were compared with our specimens by the third author, but since the authors did not have access to all the type material of the congeneric species, to compare them with the species in the present study, data (including descriptions and illustrations) from the literature (Birstein and Starostin 1949; Magniez and Stock 2000) were also used for this procedure.

Several species of the genus Stenasellus were recorded in countries adjacent to Iran: S. asiaticus Birstein & Starostin, 1949 was recorded from Turkmenistan while four species including S. vermeuleni Magniez & Stock, 2000, S. messanai Magniez & Stock, 2000, S. henryi Magniez & Stock, 2000, and S. grafi Magniez & Stock, 2000 were recorded from Oman. One species was also described from Socotra Island (Messana pers. comm.) and seven species are present in East Africa) (Messana 1990, 2001).

Hence, as Magniez and Stock (1999) stated “This possibility concerns particularly southern Iran. We must not forget that, as late as 18,000 BP, the Persian Gulf was reduced, offering a continuity of groundwater between the Oman and Iranian aquifers”, the presence of Stenasellus tashanensis n. sp. in Iran, strengthens the paleogeographic reconstructions dealing with this genus present in the karst and groundwater environments from the Far East to East Africa and Europe. Magniez and Stock (1999) showed a strict morphological similarity among the Far East, the Middle East, and the East African species, a result that may also be true for this new Iranian species.

S. tashanensis can be recognized from other Stenasellus species described from countries adjacent to Iran, by the significant differences including body size and the morphology of body appendages (Figures 5–7).

Maximum body length in S. tashanensis is 19 mm (vs up to 11 mm in S. vermeuleni, up to 8 mm in S. messanai, 3–4.5 mm in S. henryi, less than 2.5 mm in S. grafi and about 11.5 mm is S. asiaticus). The main morphological differences between S. tashanensis and other congeners from countries adjacent to Iran, are shown in Figures 5–7.

The general morphology of the S. tashanensis resembles that of S. vermeuleni, although there are significant differences in general and detailed characteristics such as the length of both antennae I and II, the number of strong spines on dactyls of the first peraeopod and the shape of the first and second male pleopods. The new species can be recognized from S. vermeuleni by the detailed following characteristics: In S. tashanensis the exopodite of male pleopod I is flatter than in S. vermeuleni, where the exopodite is strongly twisted on its longitudinal axis (Figure 5); in male pleopod II, sympodite is sub-rectangular with almost parallel margins (vs sub-pentagonal with convex external margin and concave internal margin in S. vermeuleni), proximal article of exopodite bears 4 setae (vs 2–3 in S. vermeuleni), distal article is sub-elliptical and bears 40–42 setae (vs subtriangular with 30–35 setae in S. vermeuleni), the length of proximal article of endopodite is ca. 0.75 length of sympodite (vs almost as long as sympodite in S. vermeuleni), the length of distal article of endopodite is ca. 0.9 length of sympodite (vs 1.29 times longer than sympodite in S. vermeuleni); The second pleopod of female is sub-circular (vs subtriangular in S. vermeuleni) (Figure 6); Squama of antenna II bears two strong setae (vs 3 in S. vermeuleni) (Figure 7). The chaetotaxy of the mandibular lobe is strongly different in the mandibles of the two species. In S. tashanensis left mandible has 18–20 lifting spines (vs 12 in S. vermeuleni) and right mandible has 29–30 lifting spines (vs 13–14 in S. vermeuleni). Peraeopod I of S. tashanensis bears 19 strong denticulate setae on its propus (vs 11–13 in S. vermeuleni) and 19 strong setae on its dactylus (vs 12 in S. vermeuleni).

Probably molecular genetic analysis could lead to a better comprehension of the relationship of the various taxa present in the region. Several molecular studies exist on peri-Mediterranean and American stenasellids (Messana et al. 1995; Ketmaier et al. 1997, 2003; Baratti et al. 2003; Morvan et al. 2013). We know of no molecular studies of East African or Oriental stenasellids. Future studies will hopefully clarify the phylogenetic relationships within this group of these ancient stygobionts.

Figure 5. 

Male pleopod I of Stenasellus vermeuleni (A) S. grafi (B) S. messanai (C) S. henryi (D) S. asiaticus (E) and S. tashanensis sp. n. (F). (Figures A–D from Magniez and Stock 2000; Figure E from Birstein and Starostin 1949).

Figure 6. 

Male pleopod II of Stenasellus vermeuleni (A) S. henryi (B) S. grafi (C) S. messanai (D) S. asiaticus (E) and S. tashanensis sp. n. (F). (Figures A–D from Magniez and Stock 2000; Figure E from Birstein and Starostin 1949).

Figure 7. 

Squama of antenna II of Stenasellus vermeuleni (A) S. messanai (B) S. henryi (C) S. grafi (D) and S. tashanensis sp. n. (E). (Figures A–D from Magniez and Stock 2000).

The authors thank Shiraz University for providing financial support. We would like to thank Prof Marian Glenn (Seton Hall University) for reviewing the English language of the manuscript. Our thanks are also due to Kelly L. Merrin (Australian Museum) for sending us some useful publications. We also thank Oana Moldovan, Julian Lewis and an anonymous referee, for their critical revision of the paper.