Proasellus abini, Marin & Sinelnikov, 2024

Proasellus abini sp.n.

Figs 2D–F View Fig , 3–5 View Fig View Fig View Fig .

MATERIAL EXAMINED. Holotype: ♀ (bl. 6.2 mm), ZMMU Mc-1458 , Russian Federation, southwestern Caucasus, Krasnodar Krai, Gelendzyk area , the upper stream of the Adegoy River , Novorossiyskaya Schel , 44°44′27.39″N 37°54′03.71″E, in the river hyporheic habitats, hand net sampling, coll. I. Marin, S. Sinelnikov & S. Marina, 8 Nov. 2021. GoogleMaps

Paratypes: ♀ (bl. 5.5 mm), ♂ (bl. 6.0 mm), ZMMU Mc-1459 , Russian Federation, south-western Caucasus, Krasnodar Krai, Krymsky district , the upper stream of the Shids River , 44°48′09.03″N 37°59′26.54″E, inside a small well, coll. I. Marin, S. Marina, 24 July 2021. GoogleMaps

Other material: Russian Federation, south-western Caucasus, KrasnodarKrai : 2♀♀, 6♂♂, LEMMI, Abin area, the upper stream of theAbin River , 44°43′32.3″N 38°10′04.5″E, coll. I. Marin, S. Marina, 12 Aug. 2021; GoogleMaps 5♀♀, 7♂♂, LEMMI, the upper stream of the Adegoy River , Afonka , 44°42′53.2″N 37°58′27.1″E, in the river hyporheic habitats, hand net sampling, coll. I. Marin, S. Marina, 18 July 2021; GoogleMaps 2♀♀, 4♂♂, LEMMI,Abin area, Adegoy River , near Shapsugskaya village, 44°43′31.8″N 38°02′13.8″E, in the river hyporheic habitats, hand net sampling, coll. I. Marin, S. Marina, 19 July 2021; GoogleMaps 5♀♀, 6♂♂, LEMMI, Abin area, AbinRiver , Shapsugskayavillage , 44°45′30.2″N 38°04′50.0″E, in the river hyporheic habitats, hand net sampling, coll. I. Marin, S. Marina, 19 July 2021; GoogleMaps 3♀♀, 6♂♂, LEMMI, Abin river, 44°43′43.6″N 38°06′35.6″E, in the river hyporheic habitats, hand net sampling, coll. I. Marin, S. Marina, 3 Aug. 2021. GoogleMaps

ETYMOLOGY. The new species is named after the Abin River (SW Caucasus), in the basin of which the new species was discovered.

DIAGNOSIS. Medium-sized, depigmented species. Head bisinuate, medially concave, about 1.4 times as wide as long, frontal margin lateral margins rounded, each with posterolateral setose prominence; eyes absent. AI with 8–9 flagellar articles, flagellum of AII with more than 50 articles. Inner plate of maxillula with 5 apical pappose setae. Pereopod I with propodus lumpy and swollen, about to 3.2 times as long as maximal width, inferior margin armed with 3–4 robust spiniform setae; dactylus about 0.8 length of propodus, with a row of short robust setae along inferior margin, unguis about ¼ of length of dactylus. Dactylus of pereopods II–VII with 2 robust spine-like seta along inferior margin. Pleopod I with 1 hook in retinacula. Endopodite of pleopod II in males with distinct elongated basal apophysis and with weakly expressed goulot without lips. Endopodite of pleopod II in females subtriangular, fringed with marginal simple setae. Uropods similar in shape in both males and females, but slightly differing in size: protopodite shorter in females; ratio of proto-, endo- and exopodite length is 1.0/1.1/ 1.1 in males and 1.0/1.0/ 1.2 in females.

DESCRIPTION. Stygobiotic species, blind, with depigmented body and appendages. Body elongated, about 4.5times as long as wide ( Fig.2D–F View Fig ).Head ( Fig. 2D,E View Fig )withfrontalmarginbisinuate,mediallyconcave, without rostral process, lateral margins straight, each with small posterolateral protuberance, with several short stiff setae. Eyes or pigmented spots absent.

Pereonites ( Fig. 2D–F View Fig ) depigmented, mostly smooth, lateral margins fringed with spiniform setae. Coxopods well developed, margins of all epimerae dorsally visible.

Pleotelson ( Fig. 5G View Fig ) suboval, about 1.5 times longer than wide, with distal margin bisinuate with obtusely triangular median prominence;dorsal surface smooth;lateral margins convex,fringed with spiniform setae; distal margin also fringed with numerous short setae, without large spines.

Antenna I ( Figs 2D, E View Fig ; 3A–C View Fig ) small, about 5% of body length, and about 7 times shorter than AII; basal peduncular article robust,with strongly convex inferior (shorter) margin;second and third pedunclular articles cylindrical; ratio is about 1.0/1.1/0.8; flagellum ( Fig. 3C View Fig ) consists of 8–9 articles, usually with last four or three articles bearing one aesthetascs.

Antenna II ( Figs 2D, E View Fig ; 3A View Fig ) is about 90% of body length; peduncle ( Fig. 3A View Fig ) with 6 articles, with ratio is about 1.0/1.0/1.0/2.6/4.4/0/8; flagellum long, with more than 50 articles.

Labrum ( Fig. 3D View Fig ) trapezoidal, with fine simple setae at slightly convex apex, epistome tapering, with fine setae along margin.

Labium ( Fig. 2E View Fig ) wide, subquadrate, divided almost to 2/3 of length.

Mandibulae robust ( Fig.3F View Fig ). Right mandible with pars molaris (molar process) U-shaped, with toothed margin and wrinkled crushing surface ( Fig. 3G View Fig ); pars incisiva (incisor) formed by 4 blunt cusps arranged in semicircle; palp 3-articulated; second article with numerous biserrate setae along external margin; third (distal) article sickle-shaped, with row of robust short biserrate setae along external margin. Left mandible mostly similar to right one; pars molaris U-shaped, with toothed margin and wrinkled crushing surface; pars incisiva (incisor) formed by 5 blunt cusps arranged in semicircle; palp 3-articulated.

Maxillulae ( Fig. 3H View Fig ) with inner plate with five apical pappose setae; outer plate with 12–13 dentate robust setae distally.

Maxilla ( Fig. 3I View Fig ) with inner plate slightly longer than outer plate, rounded sub-triangular, with longer row of serrate robust setae, and with oblique row of numerous simple setae; distal margin of lateral and middle plates also fringed with striated setae.

Maxilliped ( Fig. 3J View Fig ) with endite armed with 6–7 stouthook-likesetaealongthemesialinnermargin,and numerous fine distomesial setae. Palp 5-articulated; basal article short, second article about 3.0 times as longasfirstone,subtrapezoidal,withrowoflongmedially directed simple setae on inner margin; third article short about half of the second one, less broad, with row of several setae on inner margin; fourth article slender, about 2.5 times as long as wide, fringed with simple setae along outer and inner margin, respectively; fifth article ovoid, fringed with slender setae along lateral margins and stiff apical setae. Epipodite ear-shaped, distolateral margin fringed with short setae.

Pereopod I ( Fig. 4A View Fig ) subchelate, about 20% of body length, with stout articles, length relation of articles from basis (article I) to dactylus (article VII) is 1/0.8/0.5/0.15/0.9/0.7;basissmooth,subcylindrical, convex in the central part, about 3 times as long as distal width; ischium about 0.8 length of basis, subcylindrical,convex in the central part, armed with several stiff-like setae along dorsal margin;merus triangular in shape,with 2 largestiff-likesetaedistodorsally;carpus short, about as long as wide, armed with simple setae anteroventrally; propodus lumpy and swollen, about to 3.2 times as long as maximal width, inferior margin armed with 3–4 robust spiniform setae; dactylus ( Fig. 3B View Fig ) about 5 times as long as wide, about 0.8 length of propodus, with a row of short robust setae along inferiormargin,withunguisstrong,robustandslightly curved, about ¼ of length of dactylus.

Pereopods II–III similar in structure ( Fig. 4C, E View Fig ): basis smooth, subcylindrical, convex in the central part, about 3 times as long as distal width; ischium about 0.8 length of basis, subcylindrical, convex in the central part, armed with several short simple setae along dorsal margin; merus triangular in shape, with 2 large stiff-like setae distodorsally; carpus elongated, subcylindrical, about 3 times as long as wide, armed with several strong and several simple setae along inferior margin;propodus subcylindrical, with straight margins, about to 4 times as long as maximal width, inferior margin armed with 2–3 robust spiniform and several smaller simple setae; dactylus ( Fig. 4D, F View Fig ) about 2.5–3 times as long as wide, about 0.3 length of propodus, with 2 short robust setae along inferior margin, unguis strong, robust, curved, about 0.7 of length of dactylus.

Pereopods IV–VII very similar in structure ( Fig. 4G, I, K, M View Fig ): basis smooth, subcylindrical, convex in the central part, about 2–2.5 times as long as distal width;ischiumequaltobasis,swollen,usuallyconvex in the central part, armed with several short simple setae along dorsal margin; merus triangular in shape, about as long as wide, with 2 large stiff-like setae distodorsally; carpus elongated,subcylindrical, about 3–3.5 times as long as wide, slightly swollen in medial part, armed with several strong and several simple setae along inferior margin; propodus subcylindrical, with straight margins, about 6–7.5 times as long as maximalwidth,inferiormarginarmedwith 2–3 robust spiniform and several smaller simple setae; dactylus ( Fig. 4H, J, L, N View Fig ) about 3.5–4 times as long as wide, about 0.2–0.25length of propodus, with2 short robust setae along inferior margin, unguis strong, robust, curved, about half of length of dactylus.

Genital papillae in males is robust, cylindrical, straight.

Pleopod I ( Fig. 5A View Fig ) with protopodite elongated, about 2 times as long as distal width, with strongly convex outer margin, with 1 hook in retinacula ( Fig. 5B View Fig ). Exopodite subrectangular, about 1.7 times as long as wide, with numerous simple setae on lateral margin, without concavity on lateral margin.

Pleopod II different in males ( Fig. 5C View Fig ) and females ( Fig. 5D View Fig ). Male ( Fig. 5C View Fig ): with protopodite subtrapezoidal, about 1.2 times as long as wide, anteromedial corner without setae, with small papillae; exopodite suboval, elongated, about 2 times as long as wide, with distal article distally rounded, armed with several distal and lateral simple setae anterolaterally; proximal segment short, without setae; endopodite elongated, about 2 times as long as wide, subequal of protopodite in length, with distinct elongated distal apophysis and with weakly expressed goulot without lips,basal apophysis feebly marked.Female( Fig.5D View Fig ): withprotopoditesubtriangular,about 2.5 timesaslong as wide, fringed with medium marginal simple setae.

Pleopod III ( Fig. 5E View Fig ) with exopodite suboval, about 1.5 times as long as wide, with slightly convex medial margin. Lateral and terminal margins fringed with short simple setae. Endopodite about 1.6 times shorter than exopodite.

Pleopod IV ( Fig. 5F View Fig ) with exopodite broadly ovoid,about 1.8 times as long as wide,lateral margins without setae. Linea transversalis very well defined, linea conjungens clearly visible near outer margin only. Endopodite suboval, about 0.9 of length of exopodite.

Pleopod V ( Fig. 5F View Fig ) with exopodite ovoid, elongated, 2.2 times as long as wide, lateral margins without setae. Distal margin rounded. Endopodite suboval, about 0.8 of length of exopodite.

Uropods similar in shape, but slightly different in size in males ( Fig. 5H View Fig ) and females ( Fig. 5I View Fig ), equal in size to pleotelson. Male ( Fig. 5H View Fig ): ratio of proto-, endo- and exopodite length is 1.0/1.0/1.1; protopodite about 3 times as long as wide,subcylindrical,with several stout spiniform setae on inner and outer margins; exopodite subcylindrical, about 6–6.5 times as long as wide, shorter than endopodite, about 0.8 times of its length, with short simple setae on inner and outer margins and a group of long simple terminal setae; endopodite subcylindrical, about 7–7.5 times as long as wide, with short simple setae on inner and outer margins and a group of long simple terminal setae. Female ( Fig. 5I View Fig ): ratio of proto-, endo- and exopodite length is 1.0/1.0/1.2; protopodite about 4.5 times as long as wide, subcylindrical, with several stout spiniform setae on inner and outer margins; exopodite subcylindrical, about 7 times as long as wide, shorter than endopodite, about 0.8 times of its length, with short simple setae on inner and outer margins and a group of long simple terminal setae; endopodite subcylindrical, about 7–7.5 times as long as wide, with short simple setae on inner and outer margins and a group of long simple terminal setae.

BODY SIZE.The largest collected female had bl. 6.5 mm; the largest male had bl. 6.0 mm.

GENBANK ACCESSION NUMBER. OR678194-OR678197 .

DISTRIBUTION AND ECOLOGY. The species lives in the hyporheic habitats and groundwater of the Adegoy/Abin River basin,as well as a number of small neighboring rivers,for example,the Shids River.Usually, co-occuring with other stygobiotic crustaceans, such as the representatives of the genus Niphargus from the “ tauricus ” and “ submersus ” species complexes ( Amphipoda : Niphargidae ), Synurella adegoyi Marin et Palatov, 2022 ( Amphipoda : Crangonyctidae ) (see Marin & Palatov, 2022) and Gammarus cf. komareki Schäferna, 1923 ( Amphipoda : Gammaridae ).

TAXONOMIC REMARKS. The species morphologically and phylogenetically (see Fig. 1 View Fig ; Tab. 1 View Table 1 ) related to Proasellus linearis Birštein, 1967 , which also depigmented, has no yes, has only one hook in retinacula of PLI and protopodite of PLII without long plumose setae (see Birštein, 1967). At the same time, the new species can be clearly separated from P. linearis by 1) slenderer peduncular articles of AI; 2) stouter and oval pleotelson with convex lateral margins (vs. pleotelson mostly rectangular with slightly convex lateral margins); and 3) significantly longer uropods both in males and females. At the same time, it is likely that the individual described by Birštein [1967] may be immature, and a detailed re-description of the species in the future will further clarify the morphological differences between these related species.

The species can be easily separated from both Proasellus uallagyrus Palatov et Sokolova, 2021 and P. irystonicus Palatov et Sokolova 2021 , which also have 1 hook in retinacula of PLI (see Palatov, Sokolova, 2021), the new species can be separated by: 1)slenderer peduncular articles of AII, especially article 3 and 4; 2) inferior margin of dactylus of pereopod I with numerous robust stiff setae (vs only 3 setae); 3)moderately swollen carpus of PpII–VII (vs. strongly swollen); 4)inferior margin of dactyli of PpII– VII with 2 robust spine-like setae (vs a single seta).

The species can be easily separated from Proasellus precaspius Palatov, Dzhamirzoev et Sokolova, 2023 , which also has 1 hook in retinacula of PLI (see Palatov et al., 2023), the new species can be separated by: 1) inferior margin of dactylus of pereopod I with numerous robust stiff setae (vs only 4–5 setae); 2)moderately swollen carpus of PpII–VII; 3) inferior margin of dactyli of PpII–VII with 2 robust spine-like setae (vs a single seta); and 4) protopodite of PLII without long plumose setae.

The species can be easily separated from Proasellus ljovuschkini Birštein, 1967 (after Birštein, 1967) by: 1) only 1 coupling hook in retinacula of PLI (vs 2 hooks); 2) protopodite of PLII without long plumose setae; 3) inferior margin of dactylus of pereopod I with numerous robust stiff setae (vs only several setae); and 4) the lack of a large setae on mesial margin of basal article exopodite of PLII in males (vs large setae present).

The species can be easily separated from Proasellus similis Birštein, 1967 (after Birštein, 1967) by: 1) only 1 coupling hook in retinacula of PLI (vs 2 hooks); 2) almost parallel rami of uropods (vs arranged at the angle of almost 80); 3) inferior margin of dactyli of PpII–VII with 2 robust spine-like setae (vs a single seta); and 4) completely different shape of exopodite and endopodite of PLII in males (see Birštein, 1967, fig. 4).

Currently, the generic status of Proasellus infirmus Birštein, 1936 (after Birštein, 1936), originally described within the genus Asellus Geoffroy, 1762 , remains questionable, but the new species can be easy distinguished by the following features: 1) lack of eyes, white depigmented body (vs eyes with three facets and pigmented body); 2) only 1 coupling hook in retinacula of PLI (vs 2 hooks); 3) lack of long plumose setae on protopodite of PLII (vs setae plumose, long, exceed half of their length); and 4) completely different shape of exopodite and endopodite of PLII in males (see Birštein, 1936).

In conclusion, it would like to note that in order to more accurately identify and compile a diagnostic key of the Caucasian species of the genus Proasellus , it is necessary to re-describe most of the species described by J.A. Birštein at a modern level and modern equipment, as well as to obtain molecular genetic data for them. It is also obvious that the diversity of the genus is much higher than is currently expected, and even in the area of the south-western foothills, about 5–6 undescribed species most likely present, each associated with hyporhean biotopes of the separate river basins.