Stenasellus taitii, Messana & Damme & Argano, 2019

Messana, Giuseppe, Damme, Kay Van & Argano, Roberto, 2019, A new stygobiotic Stenasellus Dollfus, 1897 (Asellota: Stenasellidae) from Socotra Island, Yemen, Zootaxa 4683 (4), pp. 552-562 : 553-559

Stenasellus taitii n. sp. Messana & Argano

Holotype male MZUF 5038 , Yemen, Socotra Archipelago , Socotra Island, Erher Cave, 12°33’02.7”N, 54°27’35.7”E, alt. 250 msl., K. Van Damme leg., 27 December 2003 . Paratypes: 8 males (one slide of pleopods 1 & 2), 8 females, 1 indet., MZUF 5039 , same locality and date as holotype ; 2 males (one on 4 slides), 8 females (one on 4 slides), MZUF 5040 , Yemen, Socotra Archipelago , Socotra Island, stagnant pools near the entrance of Erher Cave, NE Socotra, K. Van Damme & S. Taiti leg, 16 January 2003. Maximum observed length of females 13.7 mm, maximum observed length of males 12.2 mm .

Etymology. The new species is named after our esteemed colleague Dr Stefano Taiti who collected the new species together with Kay Van Damme and for his excellent studies on the Isopoda of Socotra ( Taiti & Ferrara 2004; Taiti & Checcucci 2009).

Diagnosis. A pink/reddish (in life) Stenasellus (13.7 mm maximum observed length), anterior corner of cephalon with typical black spot of Bellonci Organ. Antennae long reaching pereonite 7 ( Figs 1a , 2a, b ). Lateral and middle endites of maxilla bearing respectively 7 and 9 curved dentate setae; mesial margin of maxilliped endite with three coupling hooks. Protopod of first male pleopod with two small strong dentate coupling hooks. Appendix masculina slender, elongated, with tiny distal spine ( Fig. 2c ); endopod of pleopods III–V distally biphid. Uropods ( Figs 1a , 5g ) as long as pleotelson.

Description (based on paratypes). Antennulae ( Fig. 3h ) short, reaching posterior margin of first pereonite, peduncle with four articles, first one with seven strong setae on distal margin, second one bearing four plumose and four simple setae on the same position, third article bearing one plumose seta and three distal glabrous setae, fourth article with two plumose setae. Two aesthetascs are present on distal corner of each of last four segments of flagellum.

Peduncle of antennae ( Fig. 3i ) six-segmented, third article with typical antennal scale ( Fig. 3g ) with two strong setae on lateral margin, one and five plumose seta are present on distal caudal corner of respectively fifth and sixth article.

Maxillula ( Fig. 3a ) outer lobe with a dozen spinate setae and four glabrous setae ventral on inner corner; inner lobe with three robust setae (innermost one serrate and others spinulate) and two ventral, thin and glabrous setae.

Maxilla ( Fig. 3b ) with ten spinulate falciform setae on two rows on inner lobe, and seven spinulate setae on each of the other lobes.

Maxilliped ( Fig. 3c ) with three toothed coupling hooks, ten simple setae on dorsal side and nine spinulate and one glabrous terminal setae on endite, palp bearing one spinulate seta on distal outer corner of second article and one glabrous on penultimate article.

Left mandible ( Figs 3d , 2d ) with incisor process three-toothed and sclerotized lama, lacinia mobilis strong, four-toothed with 3 small teeth on lateral margin, eight to ten denticulate and one to three glabrous lifting spines. Molar process with almost 16–25 long setae. Right mandible ( Figs 3f , 2e ) with incisor process three-toothed and sclerotized lama, lacinia mobilis three toothed, thinner than in left mandible, three to seven denticulate and 9–12 glabrous lifting spines. Molar process with up to 16 long setae. Mandibular palp ( Fig. 3e ) triarticulate, first article with one long seta on distal corner and smaller one subdistal, second article with 16–20 setae on internal margin and terminal article with almost 20–25 setae on two rows, two distal ones longer than the others.

Pereopod I haptorial ( Fig. 4a ). Dactylus with 8–15 teeth on sternal margin, propodus with 10–25 pectinate strong spines and several long setae.

Pereopods II–VII ( Fig. 4 b–g) progressively increasing, dactylus with distal accessory spine on sternal margin, propodus and carpus with single plumose seta on distal tergal corner, basis with five to seven plumose setae, carpus of pereopods 2–4 bear also bipectinate seta in same position.

Pleopod I male ( Fig. 5b ) with two strong toothed coupling hooks on inner margin of protopod. Protopod two times longer than wide, endopod twisted as in S. vermeuleni Magniez & Stock, 2000 , with several plumose setae on inner margin and several short distal naked ones.

Pleopod II male ( Fig. 5c ) protopod external margin convex, with one paramedial spine; proximal article of exopod short with one short seta on external margin, second article suboval and externally twisted with about twenty plumose setae on margin; endopod second article longer than first one, distal article slender gutter-like and fluteshaped in its caudal part, bearing small external distal spine ( Fig. 3 ) and several tiny setae.

Pleopod II female ( Fig. 5a ) subquadrangular, with four spines on sternal face and dozen of long marginal plumose setae.

Pleopods III–V ( Fig. 5 d–f) endopod distally bifid, exopod divided by a transverse suture. Distal margin of pleopod 3 with few naked setae, in pleopod 4 these are more numerous, plumose, distal and internal. Fifth pleopod without setae.

Uropods ( Fig. 5g ) as long as pleotelson, protopod about three times longer than wide, endopod subequal to exopod and bearing long distal glabrous setae, exopod about two times longer than protopod, with four plumose setae, two paradistal and two subdistal.

Remarks. The stenasellids were so far collected in Erher Cave, in the stagnant pools created by the overflow of the waterfall and in the freshwater lake at the far end. They were often hiding inside the crevices of the limestone formations and always together with the endemic blind cave shrimp Halocaridinides socotraensis ( Decapoda : Atyidae ). Other, smaller Asellota have been found in Fozzreher Cave (Van Damme, pers. obs.) in the West of Socotra ( Fransen & Van Damme 2018). Unfortunately the specimens collected were lost and could not be examined. Details on water management and chemistry of the locality are given in Fransen and Van Damme (2018).

Figures

FIGURE 1. Stenasellus taitii n. sp. Paratype male. a, body dorsal view. Scale = 2 mm.

FIGURE 2. Stenasellus taitii n. sp. Holotype male. Microphoto of: a, body dorsal view; b, body lateral view. Paratype male: c, appendix masculina, particular of terminal part; d, left mandible; e, right mandible.

FIGURE 3. Stenasellus taitii n. sp. Paratype male. a, maxillula; b, maxilla; c, maxilliped; d, left mandible; e, mandibular palp; f, right mandible with particular of the incisor process; g, third article of peduncle of antenna; h, antennula; I, antenna. Scales a–h = 100 µm.

FIGURE 4. Stenasellus taitii n. sp. Paratype male. a, first pereopod; b, second pereopod; c, third pereopod; d, fourth pereopod; e, fifth pereopod; f, sixth pereopod; g, seventh pereopod. Scales a–g = 100 µm.

FIGURE 5. Stenasellus taitii n. sp. Paratype female. a, second pleopod. Paratype male. b, first pleopod; c, second pleopod; d, third pleopod; e, fourth pleopod; f, fifth pleopod; g, uropod. Scales a–g = 100 µm.