Contributions to Zoology, 68 (3) 173-179 (1999) SPB Academic Publishing bv, The Hague Consequences of the discovery of Stenasellus (Crustacea, Isopoda, Asellota)² in the underground waters of Oman (Arabian Peninsula) * Stygofauna of Oman, 4 Guy+J. Magniez¹ &Jan+H. Stock² (†) 1 Universite de Bourgogne, Dept. Biologic Animate, 6, Bd. Gabriel, 21000, Dijon, France; institute for Systematics and Population Biology, University of Amsterdam, P.O. Box 94766, 1090 GT Amsterdam, The Netherlands Arid of marine Keywords: climate, cohabitation species, ecotones, gen. Stenasellus, ancestors, paleobiogeography, Quaternary glaciations, recent expansion, underflow Abstract Introduction An overview ofthe present knowledgeofthe family Stenasellidae The family Stenasellidae Dudich, 1924 (Asellota; Aselloidea) is presented, focusing on the success of recent investigations of the underground waters of Oman (S.E. At present, this isopod family (Asellota: Aselloidea) offour Arabian Peninsula). We take up the discovery new spe- 10 70 All includes genera and more than taxa. of interstitial cies the genus Stenasellus: small species adapted to stenasellids are and lack These anophthalmous integumen- biotopes and larger ones typical of karstic aquifers. spe- tal but or red cies cohabit in ecotones between interstitial and karstic water pigment, they possess pink haemolym- The ofstenasellids in and live in continental systems. putative presence hypogeanwaters phatic pigment underground ofYemen and South Iran is suggested. The taxonomic status of waters. The smallest of the species is 2 mm long, the Stenasellus auct. needs to be reconsidered in the fut- genus the largest 26 mm. First discovered in 1896, in the A scenario the and the of these ure. to explain origin presence sink-hole near Padirac, southwestern France, they isopods in continental underground waters is advanced. also have been collected in many other places, in the Pyrenees, the Iberian Peninsula (1924), the Balkan (1924), Turkmenistan (1949), West Africa Contents (1938), the Zaire Basin (1951), East Africa (1966), the Indochinese Peninsula (1971) and the western Introduction 173 hemisphere from Mexico and Texas (1972) (cf. The family Stenasellidae Dudich, 1924 173 Coineau et ah, 1994; Henry et ah, 1986; Lanza, The investigation of undergroundwaters in Oman 173 1966; Magniez, 1983). The species of Oman: ecology and taxonomy 174 The four species 174 The investigation of underground waters in Oman Ecological relationships 175 Taxonomic relationships 177 Between March, 23, 1996 and April, 9, 1996, Prof. Stock and made J. H. Mr. J. J. Vermeulen a very Conclusions 177 in accurate survey of underground waters the re- Presence of stenasellids in Yemen and South Iran? 177 of Jabal Akhdar J. of the 178 gion (between Nakhl, Rostaq Unity or heterogeneity genus Stenasellus auct. the Sam- Scenario for the evolution of stenasellids in and Nizwa, S.W. of city Muscat, Oman). undergroundcontinental waters 178 pling was done mainly in the coarse alluvium of temporary surface streams (wadis), using the Bou- References 178" Rouch and also in and pump system, some springs * 3 in nr. the series “Stygofauna of Oman” was published by Wewalka & Bistrom in: Koleopt. Rundsch., 68: 59-63 (1998) Downloaded from Brill.com09/23/2021 06:10:18PM via free access 174 G.J. Magniez & J.H. Stock - Stenasellidae ofOman Stenasellus Dollfus, 1897,car. emend. Racovitza, Fig. I. Map with the localisation ofthe East African and Asiatic species ofthe genus 1924. Dr. A - size 12 be wells. Similar sampling was undertaken by Stenasellus sp. average mm (may Wewalka, February 17-22, 1998. Stenasellids were longer), present in 10 localities; in the localities and the fact Stenasellus - size present 42 of point to sp. B average 8 mm, present that the settlement of these stygobiontic isopods is in 2 localities; of the - very important in this southeastern corner Stenasellus sp. C average size of adults 3-4 Arabian Peninsula (Fig. 1). mm, present in 32 localities; D - size ofadults 2-2.5 Stenasellus sp. average in 15 localities. mm, present The species of Oman: ecology and taxonomy Some 28 of the localities harbor only 1 species, The four species 11 others show the cohabitation of 2 species, and the remaining 3 localities contain 3 species together. The of than study these numerous samples (more Co-occurrences of stenasellid species were already certain localities several 42, as were sampled times) known from cave waters, viz., Mexistenasellus wil- show that four different species (Fig. 2) exist in kensi and M. parzefalli Magniez, 1972; and in in- this All the Stenasellus - area. belong to genus Dollfus, terstitial biotopes: in the phreatic layers of Guinea- emend. the 1897, car. Racovitza, 1924, same ge- Bissau or Ivory-Coast, viz., Parastenasellus chap- nus already represented in southwestern Europe, puisi (Remy, 1938) and Magniezia guinensis (Braga, Far East - Kenya, Somalia and the (Fig. 1) by some 1950) or M. africana (Monod, 1948); in the wa- 34 four taxa. These new species are to be described ter-table of the Guadalquivir River valley, S.W. in & a separate paper (Magniez Stock, in prep.). Spain, viz., Stenasellus escolai Magniez, 1976 and Their provisional appellations are: S. bragai Magniez, 1977. Nevertheless, we bring Downloaded from Brill.com09/23/2021 06:10:18PM via free access 175 Contributions to Zoology, 68 (3) - 1999 Stenasellus in the waters of Oman. Fig. 2. Relative size of the adults ofthe four species of living underground three and adults”. Wc noticed that females with here the first record of the presence of spe- “young in the This brood and even females with small cies same biotopes. situation requires a pouch conclude the study of each specimen of each sample, to avoid oostegites are absent. We two things. 1) adults of dwarf with The normal adult size of these is than any confusion between species species larger in- juveniles of large ones! the size of the largest specimen captured. For S. stance, we think that for sp. A, the maximum size could be similar to that of the karstic Euro- form Stenasellus buili 1949 mm Ecological relationships pean Remy, (14 for the male and 15-16 mm for the female). 2) The taken in the of these The study of the material shows that the samples samples are not true biotope of and Stenasellus D include as they are not of a normal Stenasellus sp. C sp. species, representative a large number of specimens, juveniles and adults. population. So, these samples are composed of erratic in an Among these, numerous females in reproductive specimens, wandering ecotone, beyond This of Oman is rich in intermolt, their brood pouches full of embryos, or their actual biotope. region has with karstic with empty after release of the larvae. This observation limestone and caves a aquifer in of them. can points to two facts: 1) We really know the size of even troglobiontic fish some We consider that the two stenasellid are these species (females of 2 mm of S. sp. D and large species females of 3 of S. C are in karstic taxa and a scheme (Fig. 3) mm sp. reproductive actually propose local between stage). More important, 2) The underflow of the to explain the occurrences together wadis of these the little interstitial and the represents the true biotope two spe- larger troglobiontic the karstic cies, as it harbours true populations. However, species. The communication between a and and an alluvial habitat is well known large species, S. sp. A S. sp. B are present only aquifer in a few number of localities. The composition of by hydrogeologists, and permits the expansion their is of from one of under- samples never representative of a popula- stygobiontic species type them for to the other 1979 and tion: we find the most part only as young ground aquifer (cf. Magniez, adults of S. C S. stages (with sizes similar to sp. or Fig. 4). sp. D), and only a small number of larger subadults Downloaded from Brill.com09/23/2021 06:10:18PM via free access 176 G.J. Magniez & J.H. Stock - StenasellidaeofOman with the Bou-Rouch in the alluvial of wadi. Local cohabitation of Fig. Sampling pump (strongly magnified) deposits a dwarf interstitial species and juveniles of large karstic species in the ecotone between free water of limestone cavities and interstitial water of alluvial gravel. Fig. 4. Ecological relationships between the four Stenasellus species of Oman; M = main biotopes, E = ecotones. Downloaded from Brill.com09/23/2021 06:10:18PM via free access Contributions to Zoology, 68 (3) - 1999 177 of the African and Arabian the the installation and Fig. 5. Paleogeographicalmap region during upper Cretaceous, showing putative in ofWest Africa ancestors ofthe African expansion of the Stenasellus ancestor continentalgroundwaters (the colonization by genera in 1998, Magniezia, Metastenasellus and Parastenasellus is recalled, as given Magniez, fig. 2). Taxonomic relationships region (Iberian Peninsula, S. France, Corsica, Sar- dinia, small part of W. Tuscany), 2) a central one: Even the though they are genetically independent (spe- the horn of Africa (Messana, 1988) and Middle- cific morphological characters and sizes quite dif- East region, and 3) the Indochinese Peninsula and related to the ancient Sunda continent reduced to is- ferent), these four species appear closely (now the each other; obviously, they arose from a single lands) (Magniez, 1989, 1993). Thus, history of original stock. the genus Stenasellus appears more complicated than from West-African Meta- When describing new species ofStenasellus that of the genera