Cottus dorofeevi, Sideleva & Zhidkov, 2024

Sideleva, Valentina G. & Zhidkov, Zakhar V., 2024, Description of a new species of Cottus Linnaeus (Cottidae) from the Western Dvina / Daugava River system, Baltic Sea basin, based on integrative taxonomy, Zootaxa 5447 (4), pp. 473-495 : 487-491

Cottus dorofeevi sp. nov.

Figs 2 , 9 , 10 , 11 ; Tables 1–2

Cottus gobio — Sapunov, 1893 (in part): 238;

Cottus gobio koshewnikowi — Berg 1949 (in part): 1147; Zhukov, 1965: 397;

Cottus gobio — Leshchenko and Palchevskaya, 2012 (in part): 79.

Holotype: ZIN 56916 , SL 68.0 mm, Ovsyanka River , a tributary of the Western Dvina, Vitebsk region, Belarus, 55.5907 N 30.4080 E, August 24, 2022, collectors Z. V. Zhidkov and S.A. Dorofeev.

Paratypes: ZIN 56917 , n = 4, 27.5–66.4 mm, Ovsyanka River, a tributary of the Western Dvina, Vitebsk region, Belarus, 55.5907 N 30.4080 E, August 24, 2022 , collectors Z. V. Zhidkov and S.A. Dorofeev ; ZIN 56918 , n = 2, SL 26.0 and 55.3 mm, Luzhesnyanka River, a tributary of the Western Dvina, Belarus, Vitebsk region, 55.2527 N 30.1431 E, depth 0.5 m, August 22, 2022 , collectors Z. V. Zhidkov and S.A. Dorofeev ; ZIN 7156 , n = 2, SL 71.7 and 74.0 mm, Lake Ostrovito , Vitebsk, August 1886, collector Radivanovsky.

Morphological diagnosis. Нead pointed anteriorly and considerably flattened in dorso-ventral direction; presence of dermal papillae on top and sides of head; large bony prickles under pectoral fins; long second dorsal fin (length of its base 40% SL); long pelvic fins reaching anus; incomplete trunk canal of seismosensory system with 25–27 pores, its end on vertical of last rays of anal fin; semicircular shape of genital papilla in males; all fins (including pelvic and anal) with dark spots.

The new species differs from the closely related C. koshewnikowi in following features: abundance of melanophores on ventral side of body (vs. absence of melanophores); presence of dermal papillae on upper and lateral parts of head (vs. absence of papillae and presence of dermal wrinkles); longer caudal peduncle (14.6±2.1 vs. 8.3±0.5% SL); large eye diameter (23.1±1.1 vs. 19.1±0.6% of head length); wider interorbital space (16.3±3.4 vs. 9.8±0.5% of head length). Cottus dorofeevi differs from another Eastern European species C. gratzianowi in following characters: absence of branched rays in pectoral fin (vs. frequent presence in C. gratzianowi ); absence of gap and presence of three pores in occipital commissure of lateral line system (vs. presence of gap and four pores in C. gratzianowi ); poorly developed lower lobes of mouth (vs. massive lobes in C. gratzianowi ).

A more detailed morphological comparison of C. dorofeevi with other European species of the genus Cottu s is provided in the Discussion section.

Molecular diagnosis. Cottus dorofeevi differs from closely related C. koshewnikowi by a combination of 11 nucleotide substitutions (three of them are unique*).

Gene of cytochrome c oxidase subunit 1 (mtDNA, partial sequence): COI 223 ( T →C), COI 430 (G→A).

Control region (mtDNA, complete sequence): CR 18 (C→G*), CR 31 (A→C*), CR 38 (gap→G), CR 37 ( T → gap), CR 52 (A→C*), CR 232 (G→A), CR 233 (A→G), CR 412 ( T →C), CR 771 (G→A).

Cottus dorofeevi and C. koshewnikowi have the following seven nucleotide substitutions that distinguish them from other European and Siberian Cottus ( C. gobio , C. cyclophthalmus , C. rhenanus Freyhof, Kottelat & Nolte , C. sibiricus , C. metae , C. perifretum Freyhof, Kottelat & Nolte ).

Gene of cytochrome c oxidase subunit 1 (mtDNA, partial sequence): COI 91 ( T →C), COI 97 (G→A), COI 454 (C→ T), COI 496 (G→A).

Control region (mtDNA, complete sequence): CR 119 (C→ T), CR 268 ( T →C), CR 778 (G→A).

Description

General morphology. Cottus dorofeevi from the Western Dvina have a large head, 1/3 SL ( Table 1 ); pointed anteriorly and considerably flattened dorso-ventrally. On average, height of head at occiput is 1.8 times less than length and width of head. Presence of dermal papillae on top and sides of head. Anterior nostrils as pigmented cylindrical tubules directed laterally; posterior nostrils as pores with raised margins. Eyes small; 21.3–25.4% of head length in paratypes (in holotype, 22.5%). Interorbital space narrow; on average, 1.4 times smaller than eye diameter. Upper jaw 10.3–11.5% SL in paratypes (in holotype, 11.6%); corner of mouth on vertical to middle of eye. Teeth on jaws and vomer conical, numerous, small, uniform in shape and size. Preoperculum with three spines; upper one directed backwards and bent inwards; second spine smaller than upper one, but well visible; all spines hidden under skin. Interbranchial space wide, 26.5–33.9% of head length in paratypes (38.4% in holotype).

Dorsal profile straight; head passes into body smoothly (without hump). Trunk shortened; preanal distance longer than postanal; maximum body height at beginning of first dorsal fin 6–6.5 times in SL. Caudal peduncle short, 11.9–16.7% SL (on average, 14%), 1.7 times as deep as long. Skin with bony prickles under pectoral fins. Semicircular shape of genital papilla in males.

No gap between dorsal fins. First dorsal fin short and low; its base length 14.2–16.6% SL in paratypes (in holotype, 17%); length of its longest ray 8.3–11.0% SL in paratypes (in holotype, 8.6%). Second dorsal fin very long; length of its base 37.1–41% SL in paratypes (in holotype, 42.6%). Beginning of anal fin 4% SL from anal opening. Rays in anal fin long, equal to or greater than those in second dorsal fin. Pectoral fins short, 26.1–31.3% SL in paratypes (in holotype, 28.5%); its end on vertical of second ray of second dorsal fin. Pelvic fins long, reaching anus, 19.7–22% SL in paratypes (in holotype, 20.3%).

Axial skeleton ( Fig. 10 ). In total, 31–34 vertebrae; 10–11 abdominal, 20–23 caudal (in holotype, 11 + 21 = 32). First four abdominal vertebrae shorter than all subsequent ones. First vertebra with well-developed neural process. Last abdominal vertebrae (from eighth–ninth to 10th–11th) with two–four pairs of pleural ribs (in holotype, three pairs). First proximal dorsal pterygiophore between first and second abdominal vertebrae, supporting first spine of first dorsal fin. One or two interdorsal pterygiophores (not supporting rays of fins) between first and second dorsal fins. Last pterygiophore of second dorsal fin before neural process of seventh preural vertebra, supporting one or two rays (in holotype, two rays) of second dorsal fin. First ray of anal fin supernumerary; its pterygiophore before first haemal process. Last pterygiophore of anal fin before haemal process of ninth preural vertebra, supporting one or two rays (in holotype, two rays) of anal fin. Caudal fin skeleton with single hypural-parhypural complex bone and three epural bones; complex bone with deep posteromedial notch. Hypural-parhypural complex bone supporting main rays of caudal fin. Seven or eight main medial rays of caudal fin branched (in holotype, seven). Additional rays of caudal fin in dorsal row supported by epural bones and neural processes of second and third preural vertebrae; additional rays in ventral row supported by haemal process of second preural vertebra.

Skeleton of fins ( Table 2 , Fig. 10 ). Cottus dorofeevi has almost similar modal values of fin-ray counts as the closely related European congeners ( C. koshewnikowi , C. gobio , and C. microstomus ). The type specimens of C. dorofeevi has 7–8 rays in the first dorsal fin, 16–18 rays in the second dorsal fin, 13–14 rays in the anal fin, 13–15 rays in the pectoral fin. The ranges of the number of fin rays are close to that of the other European Cottus ( Table 2 ).

Lateral line system ( Fig. 11 ). Sensory canals arrangement typical for Cottus . All canals (with exception of preoperculo-mandibular) interconnected in single system. In supraorbital canal, two small pores in front and behind nasale. Supraorbital canals on left and right sides connected by coronal commissure with one small pore in center. Infraorbital canal with nine pores of similar size; seventh pore on long dermal canaliculus. Temporal canal and occipital commissure with three pores. Preoperculo-mandibular canal with 10–11 pores; mandibular parts of canals interconnected in majority (seven) of specimens with one common oval pore on chin. In two type specimens, mandibular parts of preoperculo-mandibular canals not connected with two pores on chin. Presence of additional fifth pore in reoperculo-mandibular canal variable; absent in 55% of specimens (including holotype). Trunk canal not full, close to medial line of body; ending at vertical of penultimate ray of anal fin. In seven individuals, end of trunk canal with one–three autonomous segments (in holotype, two segments). Trunk canal with 19-29 small pores (modally, 25-27 pores; in holotype, 27 pores).

Coloration ( Fig. 2 ). Body and head dark gray with black spots. Two dark spots on upper part of body from base of second dorsal fin to medial line. Uniform dark gray coloration of upper and lateral parts of head, including opercular region; accumulations of melanophores on underside of head. On anterior part of body, dark pigment distributed more evenly. Unpigmented stripe on ventral side of body between pelvic fins and anus ( Fig. 2c ).

Etymology. The name of new species was given in honor of zoologist Sergei A. Dorofeev (Vitebsk State University) for his remarkable contribution to advances in the field. He organized and took part in the collection of type specimens in tributaries of the Western Dvina River, Belarus.

Distribution. This sculpin is distributed in the Western Dvina / Daugava River system within the territory of Belarus. The type locality of C. dorofeevi is middle course of the Western Dvina / Daugava River and its tributaries near city of Vitebsk ( Belarus) ( Fig. 1 ).

Figures

FIGURE 1. The map showing the distribution of Cottus sp. from the Western Dvina / Daugava River system. The numbers indicate sampling sites: 1, Ovsyanka River; 2, Luzhesnyanka River; 3, Lake Ostrovito near Vitebsk (Western Dvina / Daugava River system, Belarus).

FIGURE 2. Cottus sp. from the Western Dvina / Daugava River system, ♁, ZIN 56916, SL 68 mm, TL 79 mm; the Ovsyanka River, tributary of the Western Dvina / Daugava, Belarus, 55.5907° N, 30.4080° E; August 24, 2022; collectors Z.V. Zhidkov and S.A. Dorofeev. (a) lateral view; (b) dorsal view; (c) ventral view.

FIGURE 9. Illustration of the holotype of C. dorofeevi (ZIN 56916): (a) lateral view; (b) dorsal view of the head.

FIGURE 10. The skeleton of Cottus dorofeevi, ZIN 56917, Ovsyanka River, tributary of the Western Dvina / Daugava.

FIGURE 11. Lateral line system on the head of Cottus dorofeevi (ZIN 56916). CSO, supraorabital sensory canal; CIO, infraorbital canal, CT, temporal canal; CPM, praeoperculo-mandibular canal; CLL, trunk (lateral) canal; CMT, temporal (postorbital) commissure.