Stenasellus stygopersicus Jugovic, Malek-Hosseini & Issartel, 2024

Jugovic, Jure, Malek-Hosseini, Mohammad Javad, Issartel, Colin, Konecny-Dupré, Lara, Kuntner, Matjaž, Fatemi, Yaser, Flot, Jean-François, Douady, Christophe J. & Malard, Florian, 2024, A second species of Stenasellus Dollfus, 1897 (Isopoda, Stenasellidae) from sulfidic groundwater of Iran described using morphological and molecular methods, European Journal of Taxonomy 968, pp. 256-274 : 260-267

Stenasellus stygopersicus Jugovic, Malek-Hosseini & Issartel sp. nov.

urn:lsid:zoobank.org:act:34465D91-1AB2-4241-9A5E-63A149997A98

Figs 2–5

Diagnosis

Body dorsal smooth, pleotelson being barely longer than its width (about 1.1 its width), short antennula (in males with only up to 34 segments in flagellum), barely overreaching antennal peduncle ( Fig. 3 ). Antenna with minute squama, ultimate segment of mandible palp without setae ( Fig. 3 ). Short and wide (length <width) protopodite of pleopod I, setae only along mesiodistal margin of pleopod I exopodite ( Fig. 5 ). Pleopod II protopodite subequal in length and width, exopodite segment II with only about 10 (9–11) plumose setae; endopod of pleopods III–V in males distally deeply bifurcated (i.e. bifurcation overreaches half of endopodite III–V length). A species with strongly female-biased sexual dimorphism in body size.

Etymology

The name of the new species is formed from the prefix ‘stygo’ (from ancient Greek ‘stýx’), a common prefix used to refer to grounwater dwelling animals, and the Latin word ‘ persicus ’ referring to Persia.

Type material

Holotype IRAN • adult ♂ (bl 11.8 mm, vc 2012.11.24.80); Khuzestan Province, Behbahan County, Tashan City, near Sarjowshar Village , Chah Kabootari Cave ; 30°52′17.75″ N, 50°10′06.61″ E; 600 m a.s.l.: 17 Mar. 2018; M.J. Malek-Hosseini and Y. Fatemi leg.; UCBLZ.

Paratypes IRAN • 1 adult ♂ (bl 11.6 mm, vc 2012.11.24.84, DNA vc 2012.11.24.85); same data as for holotype; UCBLZ • 1 adult ♂ (bl 10.8 mm, pleopods vc 2012.11.24.81, DNA vc 2012.11.24.82, and body vc 2012.11.24.83); same data as for holotype; UCBLZ • 6 adult non-ovigerous ♀♀ (bl 18.2 mm, vc 2012.11.24.86; bl 22.5 mm, vc 2012.11.24.87; bl 19.5 mm, vc 2012.11.24.88; bl 19.9 mm, vc 2012.11.24.89; bl 11.9 mm, vc 2012.11.24.90, DNA vc 2012.11.24.91; bl 11.9 mm, vc 2012.11.24.92); same data as for holotype; UCBLZ • 1 adult ovigerous ♀ (bl 11.7 mm, vc 2012.11.24.93) with a brood pouch containing 22 pulli (1.86 ± 0.13 [standard deviation] mm, minimum body size: 1.65 mm; maximum body size: 2.21 mm); same data as for holotype; 8 Dec. 2018; M.J Malek-Hosseini and Y. Fatemi leg.; UCBLZ • 3 juvs ♂♂ (bl 10.2 mm, vc 2012.11.24.94; bl 9.5 mm, vc 2012.11.24.95; bl 10.5 mm, vc 2012.11.24.96); same data as for preceding; UCBLZ • 4 juvs and/or subadult ♀♀ (bl 10.8 mm, vc 2012.11.24.97; bl 11.1 mm, vc 2012.11.24.98; bl 10.1 mm, bl 10.0 mm); same data as for holotype; UCBLZ .

All material examined was from Chah Kabootari Cave (30°52′17.75″ N, 50°10′06.61″ E; 600 m a.s.l.) near Sarjowshar Village, Tashan City, Behbahan County, Khuzestan Province, Iran, and was preserved in 96% ethanol and deposited in the UCBLZ collections (https://ucblz.univ-lyon1.fr/).

Description

Males (based on holotype, values in brackets – ♂♂: range of adult males)

BODY ( Figs 2 , 3A ). Body of live specimens completely coral pink. Body length 4.0 times (♂♂: 3.9–4.0) as long as wide (width measured at greatest width, i.e., pereonite IV), head trapezoidal, with slightly concave frontal margin and black-pigmented organs of Bellonci in anterolateral corners of the head, 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. Pleonites I–II subequal in length, with projected posterolateral corner. Pleotelson ( Figs 3A , 4D ) slightly elongated, 1.07 (♂♂: 1.06–1.07) times as long as broad, posterior margin with two slight excavations; with scattered marginal spiniform setae.

ANTENNULA ( Fig. 3B ). Short, reaching the middle of pereonite I, slightly longer than the peduncle of antenna, flagellum with 12 (♂♂: 12–14) segments, segments 3–11 (♂♂: 3–11) each bearing one or two aesthetascs.

ANTENNA ( Fig. 3C ). Peduncle segments I and II shortest; the four others longer, the sixth is the longest (in percentages of antennal length: 2.8%: 2.6%:8.8%: 5.0%: 8.8%: 12.0%), and the flagellum occupying 60.0% of the total antennal length. Article VI about 1.4 (♂♂: 1.4–1.7) times the length of article V, with long simple setae distally; article III with minute squama bearing two long robust setae, flagellum reaching to pereonite IV anterior margin, with 31 articles in the holotype (♂♂: 31–34).

LEFT MANDIBLE ( Fig. 3D ). Incisor process and lacinia mobilis with three and five cusps, respectively; spine row of 11 serrated spines; molar process with a row of long, tiny, simple setae. Palp article II longer than I, bearing 6 serrate spines at distal corner; article III distolateral margins without welldeveloped setae.

LEFT MAXILLULA ( Fig. 3E ). Lateral endite apical margin with 5 serrated robust setae and 6 tiny serrated smaller setae; mesial endite with three long, robust, combs and two short simple setae.

LEFT MAXILLA ( Fig. 3F ). Lateral and middle endites each with 10 curved pectinate robust setae; mesial endite with 4 strong scarcely plumose, long robust combs, and 11 curved pectinate robust setae.

LEFT MAXILLIPED ( Fig. 3G ). Endite mesial margin with four coupling hooks, distal margin with 13 serrated and rarely plumose robust setae; palp article I with single robust seta on the inner margin, palp articles II–V with several long simple setae on the inner margin.

PEREOPOD I ( Fig. 4A ). Basis length 1.66 (♂♂: 1.58–1.66) times its width, ischium anterior margin with one robust seta on distal corner and five small robust setae on the medial projection; merus anterodistal angle with two robust setae, posterior margin with two short robust setae and 4 long slender setae; carpus triangular, posterior margin covered with several long and short simple robust seta, among them with two short robust setae along distal part; propodus almost two times as long as wide (♂♂: 1.86–1.88), its posterior margin covered with 9 stout short simple robust setae set in amongst ten simple slender long setae; dactylus around 9 times as long as basal width, posterior margin with a row of 9 contiguous scalelike flattened setae, main unguis elongate.

PEREOPOD II ( Fig. 4B ). Basis about 1.6 (♂♂: 1.60–1.67) times as long as the greatest width, anterior margin with approximately seven long distally plumose setae; ischium anterior margin with five long robust setae and one long distally plumose seta, and three strong robust setae along its distal margin; merus anterior margin with one robust seta and its anterodistal angle with three long robust setae, posterior margin with four strong and simple setae and four long distally plumose setae; carpus anterior margin with five strong and a group of weak simple setae, posterior margin covered with 11 strong and more weak long and short simple robust setae; propodus posterior margin bearing five short, simple, acute setae, anterior margin with two simple setae, anterodistal angle with two long simple and single sensory palmate setae; dactylus subequal in length to the main unguis, with two secondary unguis and one sensory plumose seta.

PEREOPOD III ( Fig. 4C ). Similar to pereopod II as illustrated. Walking pereopods II–VII similar, but progressively larger and longer.

PEREOPOD VII ( Fig. 4E ). Basis almost two times as long as the greatest width, anterior margin with five simple setae; ischium length two times its width, with 7 robust setae along its anterior margin and two simple setae along posterior margin; merus supradistal angle with two long robust setae; carpus length 4.7 times as long as width, posterior margin covered with several long and short simple robust setae, anterior margin bearing 3 simple spiniform setae, supradistal angle with three simple spiniform setae; propodus length 6 times its width, posterior margin bearing 7 simple acute setae, and superior margins bearing five acute distally plumose setae; dactylus with elongated unguis, bearing two secondary spines at posterior margin and two distally plumose setae at its anterior margin.

PENIAL PROCESSES ( Fig. 5A ). Elongated, cylindrical, about 5.3 times as long as the greatest width.

PLEOPOD I ( Fig. 5B ). Protopod shorter than its width (length/width ratio ≈ 0.8), mesial margin with a single coupling hook, exopodite elongated (length/width ratio = 2.1; ♂♂: 2.1–2.4), mesial margin without seta (or few at its distal end), a row of about 10 (♂♂: 10–13) plumose marginal setae and 5 (♂♂: 4–5) simple fine setae at mesio-apical and apical margins, lateral margin concave, bearing two setae (♂♂: 0–2).

PLEOPOD II ( Fig. 5C ). Protopod subequal in length and width (width/length ratio = 1.1; ♂♂: 1.1–1.2), exopodite article I small, without seta, article II oval, with 9 (♂♂: 9–11) plumose marginal setae; appendix masculina article II length 1.4 (♂♂: 1.35–1.40) times of article I length, tapering to curve acute apex.

PLEOPOD III ( Fig. 5D ). Exopodite with transverse suture, apical margin with 10 slender plumose setae; endopodite about 0.65 times as long as exopodite, deeply bifurcated distally.

PLEOPOD IV ( Fig. 5E ). Exopodite with transverse suture, distolateral margin with 25 slender plumose setae; endopodite about 0.8 times as long as exopodite, deeply bifurcated distally.

PLEOPOD V ( Fig. 5F ). Exopodite with transverse suture, apical margin with one slender simple seta, endopodite almost 0.9 times as long as exopodite, deeply bifurcated distally.

UROPOD ( Fig. 5G ). Protopodite and rami covered with scattered acute simple setae with few plumose setae; endopodite longer than exopodite, both rami with distal tuft of mostly simple setae and few plumose setae set among them.

Females

In the sample containing 3 adult males and 6 adult females, the body size of the longest female (22.5 mm) is almost two times that of the longest male (11.8 mm). Except from female-biased body size dimorphism (SDI = 0.91) and differences in pleopods 1–2 (females are without pleopods 1), female is mostly similar to male. Pleotelson is relatively broader, and antenna is relatively longer than in males. Pleopod 2 ( Fig. 5H ), distolateral margin bearing ca. 16 plumose setae.

Habitat

The new species was discovered in Chah Kabootari Cave or in local language Chal Kabootari ( Fig. 2 ), which means “nest of pigeons”. Aquatic habitats consist of a stream running through the cave and water pools, some of which are rich in hydrogen sulfide content. At certain periods of the year, a thick white biofilm develops at the water surface of pools, as in Tashan Cave (see Fig. 2C ). Specimens of Stenasellus stygopersicus sp. nov. were observed mostly crawling on the bottom in stinky sulfidic water of Chah Kabootari Cave. An obligate groundwater melitid amphipod, Tegano tashanensis Malek-Hosseini, Brad, Fatemi, Kuntner & Fišer, 2023 , was described from this cave in syntopy with S. stygopersicus . Water temperature was 25.6°C throughout the year and pH was 7.1. Air temperature was 25.3°C, relative humidity was 99.8%, and the air contained 768 ppm CO 2 (see Malek-Hosseini et al. 2023a).

Morphological comparison with other species

The new species is a large-sized species (bl: 22.5 mm), similar to S. tashanicus (bl: 20 mm), and both species are considerably longer than all other species known from Central and Western Asia: S. asiaticus (bl: 11.5 mm) from Turkmenistan, S. vermeuleni (bl: 11.4 mm), S. messanai (bl: 7.7 mm), S. henryi (bl: 4.9 mm), S. grafi (bl: 2.5 mm) (all four from Oman) and S. taitii (bl: 13.7 mm) from the island of Socotra ( Yemen) ( Birstein & Starostin 1949; Magniez & Stock 2000; Bakhshi et al. 2018; Khalaji-Pirbalouty et al. 2018) (Supp. file 2). All species of Stenasellus from Central and Western Asia are either monomorphic for body size (SDI = 0; S. asiaticus , S. henryi ) or exhibit a moderate female-biased sexual size dimorphism ( S. grafi, SDI = 0.04; S. tashanicus, SDI = 0.05; S. messanai, SDI = 0.08; S. taitii, SDI = 0.12; S. vermeuleni, SDI = 0.18) (Supp. file 2). However, Stenasellus stygopersicus sp. nov. exhibits a more extreme female-biased SBLD (SDI = 0.91). All the above-mentioned Asian species, including S. stygopersicus but excluding S. asiaticus from Central Asia, showed black-pigmented Bellonci’s organs at anterior lateral angles of cephalon. Although these organs were not mentioned in the description of S. tashanicus by Khalaji-Pirbalouty et al. (2018), they did appear in the description of S. tashanensi s Bakhshi & Messana, 2018, a junior synonym of S. tashanicus . Stenasellus stygopersicus have in common with S. tashanicus , S. taitii and S. vermeuleni that all have an acute apex of the appendix masculina, and bifurcated endopodites of pleopods III–V. The bifurcation however is the deepest in the new species and more than half of the endopodite lengths. We provide below a key to Central and Western Asian species of Stenasellus .

Figures

Fig. 2. A. Five specimens of Stenasellus stygopersicus Jugovic, Malek-Hosseini & Issartel sp. nov. in sulfidic water of Chah Kabootari Cave, Iran. B. A specimen of S. tashanicus Khalaji-Pirbalouty, Fatemi, Malek-Hosseini & Kuntner, 2018 in Tashan Cave, Iran. C. Another specimen of S. tashanicus, hanging on the white biofilm floating at the surface of sulfidic water in Tashan Cave, Iran.

Fig. 3. Stenasellus stygopersicus Jugovic, Malek-Hosseini & Issartel sp. nov., holotype, ♂ (UCBLZ 2012.11.24.80, body length = 11.8 mm). A. Body. B. Antennula. C. Antenna. D. Left mandible. E. Left maxillula. F. Left maxilla. G. Left maxilliped.

Fig. 4. Stenasellus stygopersicus Jugovic, Malek-Hosseini & Issartel sp. nov. A–D. Holotype, ♂ (UCBLZ 2012.11.24.80, body length = 11.8 mm). A. First left pereopod. B. Second left pereopod. C. Third left pereopod. D. Pleotelson. E. Paratype, ♂ (UCBLZ 2012.11.24.84, body length = 11.6 mm), seventh right pereopod.

Fig. 5. Stenasellus stygopersicus Jugovic, Malek-Hosseini & Issartel sp. nov. A–G. Holotype, ♂ (UCBLZ 2012.11.24.80, body length = 11.8 mm). A. Penial processus. B. First left pleopod. C. Second left pleopod. D. Third left pleopod. E. Fourth left pleopod. F. Fifth left pleopod. G. Left uropod. H. Paratype, ♀ (UCBLZ 2012.11.24.87, body length = 22.5 mm), left second pleopod.