Holotype: male, 11.5 mm, X42024/Cr-1541-FEFU, Ukraine, catacombs under Odessa, (depth -30 m from surface, lower level), Slobodka District (approx. 46.480593, 30.700242), 02.03.2014, leg. O.A. Kovtun. Paratypes: male (9.0 mm), 2 females (6.5 mm, 9.0 mm), X42025/Cr-1542-FEFU, same data as holotype.

(not included in type series). All specimens measured, partially dissected and stored in different vials [17/3sd-IBSS]: 22 females (2×9.0 mm, 7×8.0 mm, 5×6.5 mm, 8×5.5 mm), 5 males (2×8.5 mm, 3×7.5), 7 juveniles, all with same data as type series.

Diagnosis (both sexes). Large-sized species with marked sexual dimorphism (see below). Body semitransparent, alive whitish or yellowish. Eyes black, with reduced number of ommatidia; yellow mass located on the dorsolateral surface of the head between eyes. Rostrum pointed. Inferior antennal sinus distinct. Antenna 1 of males very long, comprised about 90% of total body length; more than twice as long as antenna 2; calceoli absent in both sexes. Gnathopod 2 larger (stouter and longer) than gnathopod 1; carpal lobe narrow; propodus bearing 1 strong lateral spine at “recess” near defining angle. Pereopod 7 longer than pereopod 6. Pereopod 7 basis with distinct posterior lobe. Pleopods well developed with 5–6 retinacula (coupling setae) each. Urosomal somites completely fused, but sutures visible. Coxal gills on pereopods 2–7, gill 7 very small. Sternal gills arrangement as following: pereonite 2 (-1-), pereonite 6 (1-1), pereonite 7 (1-1), pleonite 1 (1-1). Brood plates 2–5 (oöstegites) rather broad, with long marginal setae. Body length 5.5–9.0 mm (females), 7.5–11.5 mm (males).

Male, 11.5 mm long, [X42024/Cr-1541-FEFU]. Head.Eyes (Figures 2, 3A) vestigial 7 detached ommatidia, black; yellow mass located on dorsolateral surface of head between eyes. Antenna 1 (Figures 2A, 5B): 90% length of body, more than twice as long as antenna 2; peduncular articles 1−3 with a length ratio of 1: 0.9: 0.5, articles 1 and 2 with stiff short setae on medioventral face; primary flagellum with 32 articles, some flagellar articles bearing short lanceolate aesthetascs, accompanied by setae; accessory flagellum 2-articulate, longer than accompanying flagellar article. Antenna 2 (Figure 5A): gland cone short; peduncular article 4 20% longer than article 5, both sparsely setose, with stiff, simple setae; flagellum with 9 articles bearing rod-like structures accompanied with sparse setae, calceoli absent. Upper lip (labrum) (Figure 5C): sub-triangular, with minute setae at apex, clypeus elongate. Mandibles subequal: left mandible (Figure 5G) incisor 5-dentate, lacinia mobilis 5-dentate, setal row with 7 serrate setae, triturative molar strong, without accessory seta; incisor of right mandible (Figure 5H) 4-dentate, lacinia mobilis trifurcate, both parts with serrations, setal row with 6 serrate setae, molar with plumose accessory seta; palp (Figure 5I) article 1 33% length of article 2; article 2 as long as article 3, 6 setae on inner margin; article 3 with 3 A-setae, 4 C-setae, 6 E-setae and row of about 11 D-setae. Lower lip (labium) (Figure 5D): outer lobes broad, densely setose with setules, mandibular lobes obtuse, inner lobes broad. Maxilla 1 (Figure 6F): inner plate broad with 6 plumose setae; outer plate with 7 robust spines (most bifid); palp articles 1 and 2 length ratio 0.3: 1, article 2 bearing 6 stiff, simple setae apically. Maxilla 2 (Figure 6E): inner plate about twice as broad as outer plate, with oblique row of 5 plumose setae, two rows of plumose and naked setae on apex; outer plate with 12 slender setae on apex (one group longer); both plates densely setose with setules. Maxilliped (Figure 5J): inner plate with 6 strong peg-like spines on apex, 4 plumose setae extending from inner margin to apex; outer plate with a row of 16 simple setae extending from inner margin to apex; palp quadriarticulate, palp articles 1–4 length ratio 0.3: 1: 0.5: 0.6, article 2 stout with row of simple setae on inner margin, article 3 stout with group of stiff setae on outer face; dactylus without setae along inner margin, nail long with 2 minute setae at hinge. Foregut lateralia with 10 strong pectinate setae. Pereon.Coxal plates 1–2 similar, shallow, sub-rectangular (Figures 4A, B), with 5–6 marginal setae; coxal plates 3–4 (Figures 6A, B) sub-quadrate, coxa 3 narrowly rounded, with 8 stiff short setae on ventral margin, coxa 4 roundly convex distally, posterior margin without excavation, ventral margin with 9 short setae; coxal plates 5–6 (Figures 6C, D) bilobate, posterior lobe of coxa 6 larger than anterior ones and armed with 4 short setae on posterior margin; coxal plate 7 small, semilunar (Figure 6E) with 5 short setae on posterior margin. Gnathopod 1 (Figure 4A) smaller than gnathopod 2; basis stout with 4 long setae on anterior margin, some setae on inner face, 6 long thread-like setae (some in pairs) on posterior margin; carpus 0.6x as long as propodus, carpal lobe broad, bearing numerous setae; propodus smaller than propodus of gnathopod 2, sub-quadrate, weak, subchelate, palm slightly convex with cutting margin acanthaceous and armed with row of 7 distally notched robust spines on inside and 10 on outside, 18 short (1 very long) distally notched robust spines at defining angle arranged in a semicircle, anterior margin densely setose with paired setae, posterior margin short with 5 sets of simple setae; dactylus short with 7 minute setules on inner and 4 setae on outer margins, nail short with 2 setules at hinge. Gnathopod 2 (Figure 4B): basis stout with 11 long and 3 short setae on anterior margin, 3 setae on inner face and with 7 long thread-like setae (some in pairs) on posterior margin; carpus 0.35x as long as propodus, carpal lobe narrow and tapered bearing short serrate setae; propodus larger than propodus of gnathopod 1, sub-triangular, stout, subchelate, palm somewhat sinusoidal with cutting margin acanthaceous, armed with row of 13 distally notched robust spines on inside and 15 on outside (middle spines very strong), deep recess (or pouch) armed with 1 strong lateral distally notched robust spine on inner face and 4 spines (one of them long) near defining angle, posterior margin about 3 times as long as palm with 5 sets of setae; dactylus long, with 8 minute setules on inner and 5 setae on outer margins, nail short with 2 setules at hinge. Pereopods 3 and 4 (Figures 6A, B) sub-equal in length; bases sub-linear bearing short thread-like setae on both margins; dactyli short, about 33% length of corresponding propodi, inner margin with 1 long seta and 1 minute setula at hinge. Pereopods 5-7 (Figures 6C–E): pereopod 6 88% length of pereopod 7; basis 7 20% longer than basis 6; bases of pereopods 5 and 6 slightly broader proximally than distally, margins serrated with setules, distoposterior lobes poorly developed, basis 7 oblong with distoposterior lobe distinct; dactyli short about 25–30% length of corresponding propodi, inner margin with 1 long seta and 1 minute setula at hinge. Coxal gills 2–7 (Figures 4B, 6A–E) stalked and sub-ovate, coxal gill 7 very small. Simple, very small medial sternal gill on pereonite 2; simple, large, lateral sternal gills present on pereonites 6, 7 and pleonite 1. Genital papillae on ventral surface of pereonite 7 (smaller than, and located posterior to sternal gill). Pleon.Epimera 1–3 (pleonal plates) (Figures 2, 3B): posterior margins of plates convex with 3–4 stiff setae; distoposterior corners acute; ventral margin of plate 1 nearly straight with 3 strongly notched spines; plates 2 and 3 convex, bearing 7 and 9 strong notched sub-marginal spines; plates 2 and 3 with 1 long upward-directed seta above posterolateral angle. Pleopods 1–3 (Figure 3C): sub-equal, peduncular articles each with 6 retinacula (coupling setae), 3 simple setae on distal margin; proximal article of inner ramus on inner face naked or bearing 1 seta; inner rami slightly longer with 10 articles, outer rami with 12 articles, both rami fringed with plumose setae. Urosome (Figure 2): urosomites completely fused but sutures visible, lacking dorsal armament. Uropod 1 (Figures 2, 3D): peduncle with 13 setae on outer margin, 2 setae on inner margin; outer ramus as long as inner ramus, 77% length of peduncle; both rami armed with 10 weak spines on both margins, inner ramus with 4 spines and outer ramus with 5 spines on apices. Uropod 2 (Figures 2, 3E): peduncle with 5 setae on outer margin and 1 distal bifid and 1 simple (corner) setae on inner margin; outer ramus shorter than inner ramus, 80% length of peduncle; both rami armed with 4–8 weak spines and setae on both margins, inner ramus with 5 spines and outer ramus with 4 spines on apices. Uropod 3 (Figure 3F) uniramous, peduncle cone-shaped, about 1.3x as long as endopodite, with a terminal “squamous knob” and 1 weak spine on distal margin; lateral and apical margin of ramus armed with 1 and 3 weak spines correspondingly. Telson (Figure 3G) not tapered distally, elongate, 0.7x as long as broad, as long as uropod 3; apical margin cleft, about 1/3 of total length, with mix of short and long 10–11 curved spines on each lobe.

Female, 9.0 mm long, [X42025/Cr-1542-FEFU], sexually dimorphic characters. Smaller than male, with more slender body. Antenna 1 50% of total body length; almost twice as long as antenna 2. Gnathopods 1 and 2 (Figures 7E, F) propodi poorly setose and palmar margins weakly armed with spines. Oöstegites 2–5 on gnathopod 2 and pereopods 3– 5 broad, expanded distally, with long marginal setae. Telson (Figure 7D) bearing 7–8 spines on each lobe.

Examined specimens have variations in setation of peduncular articles of pleopods, which can be naked or with single thin seta and bearing 5–6 retinacula (coupling setae) each. The ventral margin of epimera varies slightly in number of spines according to age and body size.

Among the eight known species of Synurella of the Volga-Black Sea area, S. odessana sp. n. has a number of unique features: (1) developed spines at defining angle of gnathopod 1 forming a semicircle; (2) inner face of gnathopod 2 propodus with a deep “recess” fitted with 1 strong, lateral spine; (3) pleonal plates 1 and 2 each with an erect, long seta at corner, (4) uropod 3 with small squamous projection (rudiment of exopod).

Within the genus Synurella, S. odessana sp. n. is clearly related to three species (S. donensis Martynov, 1919, S. dershavini Behning, 1928, S. osellai Ruffo, 1972) known from springs of the Volga-Black Sea basin. Along with these species, the new species is appointed in a new group, the dershavini-group. This group is characterized by the largest set of plesiomorphic states of selected morphological features (see Table 1). S. odessana sp. n. resembles S. donensis and S. osellai in the shape of the lower lip. The densely setose anterior margin of carpus and propodus of gnathopod 1 are similar to feature of S. osellai, from which it differs by the 6-dentate pars incisiva of the left mandible. For some species that belong to the dershavini-group the defining features have been insufficiently described in earlier publications, thus it is difficult to identify which species within the group resembles most closely to S. odessana sp. n. The incisor of the right mandible of S. odessana sp. n. is 4-dentate, typical for both species in the genus Lyurella.

Ukraine, catacombs under Odessa, Slobodka District [approx. 46.480593, 30.700242].

The epithet odessana (lat.) refers to the city name, Odessa, where species was collected.

S. odessana, is known only from the type locality. The specimens were collected in various flooded parts of the catacombs, at a fairly remote distance from each other. In areas where karst sinkholes were present, where the water contains large amount of organics (earth, rotten wood, etc.), the species was abundant, reaching about 50 individuals/m². In areas with relatively oligotrophic water, animals were rare or absent. The epimeral plates and pleopods of almost all specimens were densely parasitized by the suctorial infusoria Dendrocometes (Protozoa: Ciliata) (Dovgal and Mayén-Estrada 2013). Unidentified stygobiontic Copepoda (Crustacea) were also collected from the same locality. Physical parameters of the water at the collecting site included: temperature 12.5 °C, hardness 3.74 ‰ (Kovtun and Sidorov 2014).

All females of S. odessana, were mature and characterized by developed brood plates (oöstegites) with a long marginal setae, but without eggs or youngs. As all specimens were collected on a single date and a fairly large series of females was available, these data suggest that this species has a seasonal cycle of reproduction.

Figure 3. 

Synurella odessana sp. n.: male, 11.5 mm, holotype X42024/Cr-1541-FEFU: A head B epimera 1‒3 C pleopod 3 D uropod 1 E uropod 2 F uropod 3 G telson. Scale bars 0.2 mm.

Figure 4. 

Synurella odessana sp. n.: male, 11.5 mm, holotype X42024/Cr-1541-FEFU: A gnathopod 1 B gnathopod 2. Scale bars 0.2 mm.

Figure 5. 

Synurella odessana sp. n.: male, 11.5 mm, holotype X42024/Cr-1541-FEFU: A antenna 2 B antenna 1 C upper lip D lower lip E maxilla 2 F maxilla 1 G mandible, left H mandible, right I mandible, palp J maxilliped. Scale bars 0.2 mm.

Figure 6. 

Synurella odessana sp. n.: male, 11.5 mm, holotype X42024/Cr-1541-FEFU: A pereopod 3 B pereopod 4 C pereopod 5 D pereopod 6 E pereopod 7. Scale bars 0.2 mm.

Figure 7. 

Synurella odessana sp. n.: female, 9.0 mm, paratype X42025/Cr-1542-FEFU: A urosome B antenna 2 C uropod 3 D telson E gnathopod 1, propodus F gnathopod 2, propodus G lateralia. Scale bars 0.2 mm.