Cottus cyclophthalmus, Sideleva & Kesminas & Zhidkov, 2022

Sideleva, Valentina, Kesminas, Vytautas & Zhidkov, Zakhar, 2022, A new species of the genus Cottus (Scorpaeniformes, Cottidae) from the Baltic Sea Basin and its phylogenetic placement, European Journal of Taxonomy 834, pp. 38-57 : 43-50

Cottus cyclophthalmus sp. nov.

urn:lsid:zoobank.org:act:B28C4DA1-772B-47FD-9CF3-39EA5BD7ED93

Figs 2–3 ; Table 1

Cottus gobio – Zograf 1907: 17.

Cottus gobio – Zhukov 1958: 156.

Cottus gobio – Alekseev & Probatov 1969: 7.

Diagnosis

C ottus cyclophtalmus sp. nov. has round, protruding (tubular) eyes near front of head; dermal papillae present on top and sides of head, body naked, bony prickles absent; full trunk canal with 32–36 pores.

Etymology

The name of the new species is derived from the Latin word for ‘round-eyed’ and is associated with the round and convex shape of eyes.

Type material

Holotype RUSSIA • ♂, SL 83.3 mm, TL 99.0 mm; Krasnaya River, near Tokarevka village, Kaliningrad Region; 54°24′59.4″ N 22°23′50.4″ E; 31 Aug. 2019; ZIN 56687.

Paratypes RUSSIA • 8 specimens, SL 81.0- 48.7 mm; same collection data as for holotype; ZIN 56688 .

Non-type specimens

LITHUANIA • 26 specimens, SL 56.9–72.1 mm; Žeimena River , tributary of the Neris River , Nemunas / Neman River Basin; 54º58′01.4″ N, 25º44′11.1″ E; Sep. 2019; ZIN 56689 • 24 specimens, SL 51.4– 74.1 mm; Neris River , tributary of the Nemunas/Neman River ; 54º50′06.4″ N, 25º22′31.5″ E; Sep. 2019; ZIN 56690 • 22 specimens, SL 56.1–69.7 mm; Siesartis River , Nemunas/Neman River Basin ; 55º17′23.8″ N, 24º53′02.7″ E; Sep. 2019; ZIN 56691 • 16 specimens, SL 48.8–79.2 mm; Šerkšnė River , tributary of the Venta River ; 56º19′35.2″ N, 22º12′47.7″ E; Sep. 2019; ZIN 56692 .

Description

Body shortened, its average maximum depth at origin of first dorsal fin four times SL. Body massive, preanal distance more than half SL. Caudal peduncle short, its length 14–17% SL (14.9% in holotype), average height of caudal peduncle half its length ( Table 1 ). Trunk naked, bony prickles (modified scales) absent.

Head large with smooth dorsal profile from head to back, its length more than 30% SL in type specimens (33% in holotype). Dermal papillae numerous on top and sides of head, sometimes in form of circles.

Postorbital length large, always more than half head length (53% HL in holotype). Snout short, more than half postorbital length (59.4% in holotype). Anterior nostrils small, tubular, highly pigmented; posterior nostrils in form of short tubes. Mouth small, terminal; upper jaw does not reach vertical line of anterior edge of eye. Teeth on jaws and vomer small, numerous, of same shape and size. Upper lip thick, fleshy, twice thicker than lower lip.

Eye round and protruding, near to front of head, average eye diameter 7.3% SL (7.4% SL or 22.4% HL in holotype). Interorbital space narrow, on average 1.5 times less than eye diameter. Preoperculum with three spines; upper spine sharp, directed backwards and slightly curved inward. Second and third spines small, in form of tubercles hidden under the skin. Interbranchial length large, on average 1.5 times less than length of gill slit (16.6% in holotype).

Two dorsal fins follow each other without gap. First dorsal fin low, length of its longest rays 1.5 times as long as rays of second dorsal fin. Narrow light border along edge of first dorsal fin. Second dorsal fin long, its base 2.5 times as long as base of first dorsal fin. Origin of anal fin at short distance (3% SL) from anus, on vertical line of second ray of second dorsal fin; length of longest rays in anal fin 1.2 times that in second dorsal fin. Pectoral fin short, reaching vertical of first ray of second dorsal fin. Pelvic fin long (20% SL), not reaching anus.

Axial skeleton: total number of vertebrae counts 31–32: 10–11 abdominal and 21–22 caudal (11 + 21 = 32 in holotype). The first vertebra with fully developed neural spine. The posteriormost abdominal vertebrae (from 8 th –9 th to 10 th –11 th) are carrying two or three pairs of pleural ribs (three in holotype).

The first proximal pterygiophore of the dorsal series is placed between first and second vertebrae. It supports first dorsal fin spine which is in supernumerary position (morphotype A according to Yabe 1985). One interdorsal pterygiophore is placed between first and second dorsal fin. The last proximal pterygiophore of dorsal series supports one or two rays (one in holotype). The last pterygiophore of anal fin supports one or two fin rays (two in holotype).

The caudal skeleton is composed of single hypural-parhypural complex bone and three epurals. The complex bone has deep notch posteromedially and supports principal caudal-fin rays. Medial principal rays of caudal fin are branched.

Number of rays in fins: first dorsal fin with six to eight spines (seven in holotype); second dorsal fin with 16 to 19 rays (17 in holotype); anal fin with 12 to 15 rays (13 in holotype); pectoral fin with 12 to 15 rays (14 in holotype); four rays in pelvic fin; caudal fin with 12 principal rays (eight branched and four unbranched).

Lateral line of Cottus cyclophthalmus is typical of the genus Cottus . All sensory canals (with exception of preopercular-mandibular canal) are interconnected and form a unified system.

Three small pores are in supraorbital canal, they located in anterior part of canal, up to coronal commissure. It connects left and right supraorbital canals to each other. One small pore is in center of coronal commissure. The infraorbital sensory canal opens outward with nine pores, of which second and third pores are large slit-like. The temporal canal and occipital commissure each have three pores. The preopercular-mandibular sensory canal opens with 10 pores. The canals of left and right sides are interconnected, and on chin they open with common oval pore. The trunk canal is full (reaches the base of the caudal fin), located closer to dorsal part of body and opens with 31–34 small pores.

Coloration: the upper part of the body is dark to the medial line. Below, there are numerous small spots formed by clusters of melanophores. The upper part of the head, including the upper lip, is dark, the radii branchiostegii are light. The ventral side of head and body are light. The dorsal fins variegated and have dark transverse stripes. A narrow light border is at the edge of the first dorsal fin. Weakly expressed dark spots and stripes are present at origin of pectoral and caudal fins. The external parts of the pectoral, anal and pelvic fins are light, not pigmented.

Distribution

Cottus cyclophthalmus sp. nov. is distributed in the rivers Krasnaya, Neris, Žeimena and Sesartis (Neman/Nemunas River system) and Šerkšnė River (Venta River system), Baltic Sea Basin ( Fig. 1 ).

Variation of morphometric features and numbers of rays in Cottus cyclophthalmus sp. nov.

For a comparative analysis of morphometric characters of type and non-type specimens of Cottus cyclophthalmus sp. nov. from the rivers Krasnaya, Neris, Šerkšnė, Siesartis and Žeimena, PCA was used ( Fig. 4 ). The variability of 26 external features was analyzed. ( Table 2 ). The principal component analysis revealed a variability of initial data. This data is represented in a scatter plot with uncorrelated second and third principal components. Each component reflects a proportion of a variability of variance-covariance matrix of features. The conducted analysis showed that the first principal component describes 84.6% of total variability of measurements in five studied samples of sculpins. The first component is characterized by close positive values of factor loadings (from 0.758 to 0.982, or 0.918 on average). All other 25 components describe 15.4% of total variability. Figure 4 shows morphospaces of studied samples in the space of second and third components. The morphospaces of samples of C. cyclophthalmus overlap significantly. There are no discrete geographic groupings. This indicates that the five studied samples are not differentiated by morphometric characters and belong to the same species C. cyclophthalmus .

Data on variation in number of rays in dorsal, anal, and pectoral fins in five samples of Cottus cyclophthalmus sp. nov. are presented in Table 3. A comparison of presented data shows that sculpins from different localities have a similar degree of variation in the number of rays in fins. The differences in number of rays in each fin ranged from 2 to 4 values. In the first dorsal fin in the type specimens from Krasnaya River, the number of rays varied only within two ranges (six to seven rays). In non-type individuals from tributaries of the Nemunas/Neman and Venta rivers, the number of rays varied from six to eight. In all samples (except for sculpins from Šerkšnė River), fish with seven rays in the first dorsal fin dominated (76–94% of all specimens). The number of rays in the second dorsal fin ranged from 16 to 19. Type specimens from Krasnaya River had the smallest (16–17) number of rays in the second dorsal fin. The difference between the samples lies in modal values, with the majority of studied fish (69.5%) having 17–18 rays in the second dorsal fin. In the anal fin, the number of rays varied from 12 to 16. Type specimens of Cottus cyclophthalmus had 13–14 rays in anal fin. The same number of rays dominated in 94% of the studied fish. In the pectoral fin, the number of rays varies from 12 to 15. Fish with a modal number of 14 rays dominated in all samples.

Thus, in all five samples of C. cyclophthalmus sp. nov., the number of rays in two dorsal, the anal and pectoral fins had a similar level of variation. The differences in number of rays in sculpins from different localities were in modal values. This level of variability corresponds to differences between individual populations of C. cyclophthalmus .

Variation in mitochondrial DNA sequences

To identify intraspecific genetic diversity of C. cyclophthalmus sp. nov., we studied nucleotide sequences (858 bp) of mtDNA control region. Table 4 contains the data on haplotypes found in samples of C. cyclophthalmus from four rivers (Krasnaya, Žeimena, Siesartis, and Šerkšnė). Nine haplotypes were identified (CCY1–CCY9). The most common haplotype was CCY6 (52% of specimens of the new species). It was found in sculpins from each of the studied rivers. The sample of a new species from the Šerkšnė River was characterized by the greatest haplotype diversity (6 unique haplotypes). The number of detected polymorphic sites (S) was seven. The nucleotide diversity of mtDNA control region among individuals of C. cyclophthalmus had a low value (π = 0.00139 ± 0.00024). The haplotype diversity (Hd) was high (0.718 ± 0.080). The average number of nucleotide differences was 1.196.

All data indicate a low level of genetic differentiation between the studied specimens. This is the evidence that all individuals belong to species C. cyclophthalmus .

Figures

Fig. 2. Cottus cyclophthalmus sp. nov., holotype, ♂ (ZIN 56687), SL 83.3 mm, TL 99.0 mm, Krasnaya River, near Tokarevka village, 54º24'59.4" N 22º23'50.4" E. 3D scan images. a. Lateral view. b. Dorsal view. c. Ventral view.

Fig. 3. The zoological picture of the holotype of Cottus cyclophthalmus sp. nov. (ZIN 56687), SL 83.3 mm, lateral view.

Fig. 1. The map of sampling sites showing the distribution of Cottus cyclophtalmus sp. nov. The numbers indicate sampling sites in various rivers: 1. Krasnaya River. 2. Neris River. 3. Žeimena River. 4. Siesartis River. 5. Šerkšnė River. The star marks the type locality of the new species; the circles mark sampling sites of non-type specimens; the triangle marks the locality where specimen of Cottus microstomus sp. nov. was caught.

Fig. 4. The result of statistical analysis of morphometric characters of type and non-type specimens of Cottus cyclophthalmus sp. nov. from rivers Krasnaya, Neris, Šerkšnė, Siesartis, and Žeimena (method of principal components was used). The numbers correspond to the places where the sculpins were caught, as indicated on the map (Fig. 1).

Tables

Table 1. Proportional measurements as percentages of standard length of holotype and paratypes of Cottus cyclophthalmus sp. nov. from Krasnaya River.

	Holotype			Paratypes (n= 8)
Standard length (SL), mm	83.3	81.0	68.5	66.4	63.3	54.4	53.3	50.4	48.7
In % SL
Predorsal length	35.5	37.3	36.8	37.2	37.0	36.0	34.9	34.9	36.8
Postdorsal length	9.7	8.9	11.5	11.3	11.1	11.0	12.2	11.1	10.3
Preanal length	55.0	58.4	51.7	54.2	55.9	55.5	54.4	52.0	56.7
Postanal length	47.3	42.6	48.5	47.7	48.2	48.9	47.3	48.2	46.0
Maximum body depth	24.2	24.8	21.3	22.9	22.9	23.2	21.2	22.0	22.2
Length of caudal peduncle	14.9	14.3	17.2	16.6	16.3	14.5	15.2	15.3	14.0
Depth of caudal peduncle	8.5	7.9	7.0	7.4	7.1	7.4	7.3	6.9	7.0
Length of first dorsal fin base	14.8	13.6	13.9	15.1	12.5	13.2	12.8	14.1	12.1
Length of second dorsal fin base	36.9	36.7	34.6	34.9	35.4	35.5	36.2	36.9	37.2
Length of anal fin base	30.1	27.7	29.2	28.6	28.9	28.9	29.6	27.6	27.9
Length of longest firs dorsal fin spines	8.3	8.9	8.8	9.3	8.8	7.4	9.2	9.7	8.6
Length of longest second dorsal fin rays	12.5	13.3	13.3	13.9	12.2	13.2	13.3	13.7	12.5
Length of longest anal fin rays	14.5	15.8	13.4	15.2	14.2	13.2	12.4	14.3	12.7
Pectoral fin length	28.6	27.3	25.8	27.7	26.1	26.5	25.7	26.6	27.3
Pelvic fin length	20.3	20.2	20.4	21.2	19.6	20.8	19.7	18.3	19.9
Head length	33.0	35.7	32.6	33.6	33.0	32.4	31.3	32.1	34.7
Postorbital length	17.5	18.8	17.7	17.2	17.4	16.5	15.6	16.5	17.7
Head depth	21.4	22.1	19.4	20.5	20.5	20.2	18.9	18.3	21.6
Head width	30.6	34.6	32.3	31.2	32.2	30.9	30.8	28.6	32.0
Eye horizontal diameter	7.4	7.2	7.0	6.9	7.0	7.5	7.3	7.9	7.2
Snout length	10.4	11.0	10.2	10.1	10.3	9.9	9.8	9.7	10.7
Interorbital width	4.9	6.0	4.4	5.1	5.2	5.3	4.7	4.8	6.0
Upper jaw length	13.2	14.6	11.5	12.3	12.5	11.4	10.5	11.3	12.7
Interbranchial width	11.4	12.8	9.9	12.0	11.5	12.1	9.9	9.1	8.6
Length of gill slit	19.0	20.4	16.8	18.4	18.5	16.4	16.5	17.7	18.5

Table 2 (continued on next page). Proportional measurements of type and non-type specimens of Cottus cyclophthalmus sp. nov. from Pregolya, Neman and Venta River systems (Russia, Lithuania). Note: numerator = mean (M) ± standard deviation (SD); denominator = range.

	Krasnaya R. (n = 9)	Neris R. (n = 19)	Zeimena R. (n = 10)	Siesartis R. (n = 10)	Šerkšnė R. (n = 10)
	Type specimens		Non-type	specimens
SL, mm	63.3 48.7–83.3	61.6 51.4–74.1	65.6 56.9–72.1	62.3 56.1–69.7	61.4 48.8–79.2
In % SL†
Predorsal length	36.3 ± 0.9 34.9–37.3	36.3 ± 1.3 34.8–39.7	34.9 ± 1.2 32.4–36.5	35.4 ± 0.5 34.7–36.2	34.9 ± 1.2 32.4–36.5
Postdorsal length	10.8 ± 1.0 8.9–12.2	10.3 ± 0.8 9.0–12.5	9.9 ± 1.2 8.2–11.9	10.0 ± 0.3 9.6–10.3	9.9 ± 1.2 8.2–11.9
Preanal length	54.9 ± 2.1 51.7–58.4	53.6 ± 1.5 51.0–56.2	55.0 ± 2.0 51.9–57.2	54.2 ± 0.4 53.5–54.9	55.0 ± 2.0 51.9–57.2
Postanal length	47.2 ± 1.9 42.6–48.9	48.2 ± 1.6 45.1–50.5	46.8 ± 1.6 43.6–48.6	47.7 ± 0.7 46.2–48.8	46.8 ± 1.6 43.6–48.6
Maximum body depth	22.7 ± 1.2 21.2–24.8	21.9 ± 1.2 20.0–23.8	20.5 ± 0.9 19.3–21.7	21.5 ± 0.5 20.7–22.3	20.5 ± 0.9 19.3–21.7
Length of caudal peduncle	15.4 ± 1.1 14.0–17.2	15.1 ± 1.1 13.0–16.9	14.7 ± 1.4 12.7–16.6	14.9 ± 0.2 14.5–15.3	14.7 ± 1.4 12.7–16.6
Depth of caudal peduncle	7.4 ± 0.5 6.9–8.5	7.4 ± 0.5 6.8–8.7	7.0 ± 0.4 6.4–7.9	7.0 ± 0.2 6.6–7.4	7.0 ± 0.4 6.4–7.9
Length of first dorsal fin base	13.6 ± 1.0 12.1–15.1	13.8 ± 0.7 12.3–15.4	13.5 ± 0.8 12.1–14.7	13.6 ± 0.2 13.3–13.9	13.5 ± 0.8 12.1–14.7
Length of second dorsal fin base	36.0 ± 0.9 34.6–37.2	36.8 ± ± 1.5 32.3–39.1	36.5 ± 1.7 33.0–38.5	38.1 ± 0.4 37.2–38.7	36.5 ± 1.7 33.0–38.5
Length anal fin base	28.7 ± 0.9 27.6–30.1	28.7 ± 1.4 26.3–31.2	28.3 ± 1.4 26.6–31.0	29.9 ± 0.4 29.1–30.4	28.3 ± 1.4 26.6–31.0
Length of longest first dorsal fin spines	8.8 ± 0.7 7.4–9.7	8.8 ± 0.9 7.2–10.3	8.0 ± 0.9 6.6–9.3	9.1 ± 0.3 8.7–9.8	8.0 ± 0.9 6.6–9.3
Length of longest second dorsal fin ray	13.1 ± 0.6 12.2–13.9	13.6 ± 0.7 12.6–15.2	13.3 ± 0.9 11.4–14.5	13.4 ± 0.3 12.9–14.1	13.3 ± 0.9 11.4–14.5
Length of longest A ray	14.0 ± 1.1 12.4–15.8	13.8 ± 0.8 12.8–15.6	13.5 ± 0.6 12.4–14.5	14.1 ± 0.6 13.2–15.0	13.5 ± 0.6 12.4–14.5
Pectoral fin length	26.8 ± 1.0 25.7–28.6	28.6 ± 1.5 25.4–32.3	25.9 ± 1.4 23.8–28.9	26.2 ± 0.8 25.1–27.9	25.9 ± 1.4 23.8–28.9
Pelvic fin length	20.0 ± 0.8 18.3–21.2	20.2 ± 1.3 17.9–23.2	19.0 ± 0.8 18.0–20.6	19.7 ± 0.5 18.8–20.4	19.0 ± 0.8 18.0–20.6
Head length	33.2 ± 1.3 31.3–35.7	32.6 ± 1.0 30.6–34.4	32.0 ± 1.2 30.0–33.7	32.3 ± 0.9 31.2–33.9	32.0 ± 1.2 30.0–33.7
Postorbital length	17.2 ± 0.9 15.6–18.8	17.1 ± 0.6 16.0–18.1	16.1 ± 1.0 14.7–17.7	16.9 ± 0.7 16.1–18.3	16.1 ± 1.0 14.7–17.7
Head depth	20.3 ± 1.3 18.3–22.1	19.5 ± 1.1 17.1–21.3	19.2 ± 1.0 17.7–20.6	19.5 ± 0.6 18.6–20.4	19.2 ± 1.0 17.7–20.6
Head width	31.5 ± 1.6 28.6–34.6	29.3 ± 2.2 24.9–33.3	29.3 ± 1.3 26.5–30.9	29.0 ± 0.7 27.8–30.1	29.3 ± 1.3 26.5–30.9