Eptatretus wandoensis, Song & Kim, 2020

Song, Young Sun & Kim, Jin-Koo, 2020, A new species of hagfish, Eptatretus wandoensis sp. nov. (Agnatha, Myxinidae), from the southwestern Sea of Korea, ZooKeys 926, pp. 81-94 : 81

Eptatretus wandoensis sp. nov. Figures 1 , 2 , 3 , 4 , 5 , Table 1 New English name: Five-gilled white mid-dorsal line hagfish; new Korean name: Huin-jul-wae-meok-jang-eo

Type locality.

The coast of Yeoseo-do (southwestern Sea of Korea): Yeoseo-ri, Cheongsan-myeon, Wando-gun, Jeollanam-do, Republic of Korea, 33°59'56.5"N, 126°53'57.0"E, caught by fishing traps, 60-80 m (Fig. 1 ).

Holotype.

PKU 62167, 292.0 mm TL, Yeoseo-ri, Cheongsan-myeon, Wando-gun, Jeollanam-do, Republic of Korea, 33°59'56.5"N, 126°53'57.0"E, caught by fishing traps, 60-80 m, 26 Jun 2018.

Paratypes.

PKU 62169 (1 specimen), 202.0 mm TL, Yeoseo-ri, Cheongsan-myeon, Wando-gun, Jeollanam-do, Republic of Korea, 33°59'56.5"N, 126°53'57.0"E, fishing trap, 60-80 m, 12 May 2018; PKU 62171, PKU 62173, 275.0-290.0 mm TL, Yeoseo-ri, Cheongsan-myeon, Wando-gun, Jeollanam-do, Republic of Korea, 33°59'56.5"N, 126°53'57.0"E, fishing trap, 60-80 m, 26 Jun 2018.

Diagnosis.

Gill apertures, 5; eyespots, conspicuous; fused cusps, 3/2; total cusps, 40-43; 1 GP at end of dental muscle; total slime pores, 74-82 (prebranchial, 14-18; branchial, 4; trunk, 46-49; tail, 9-11); branchial length, 5.2%-6.2% of TL; pharyngocutaneous duct confluent with last gill aperture; ventral artery splitting at approximately 3-4 GP; dorsal region with dark brown body color, ventral region with white body color; white mid-dorsal line, conspicuous.

Description.

Body elongated; laterally compressed at trunk and strongly compressed at tail (Fig. 2 ). Rostrum slightly blunt and round (Fig. 3A ). Nasal-sinus papilla absent. Eyespots present (Fig. 3A ). Pre-eyespots shorter than branchial region (4.4%-4.9% of TL). Three pairs of barbels on head: first (1.5%-1.6% of TL) and second barbels (1.6%-1.9% of TL) nearly equal in size; third barbel is longer (2.1%-2.3% of TL) and tips of third barbels extend at the mouth (Fig. 3B ). Five pairs of GP and apertures; each gill aperture arranged regularly spaced in a straight line (Fig. 3C ). Teeth row comb-like, consisting of two rows with tips sharp and curved rearward (Fig. 4A ); in the outer row, 3 multicusps and 7-8 unicusps; in the inner row, 2 multicusps and 8-9 unicusps; total number of cusps, 40-43. Dental muscle thick and long, posterior tip of dental muscle located in first GP (Fig. 4B ). Slime pores: prebranchial, 14-18; branchial, 4; trunk, 46-49; tail, 9-11; total, 74-82. Body proportions are as follows: prebranchial length, 24.4%-26.3% of TL; branchial length, 5.2%-6.2% of TL; trunk length, 54.9%-59.3% of TL; tail length, 12.8%-14.0% of TL; cutaneous duct, 7.6%-9.3% of TL; branchial duct (with ventral fin-fold), 6.9%-9.7% of TL; and branchial duct (alone), 5.6%-7.7% of TL (Table 1 ). Posterior-most EBD confluent with pharyngocutaneous duct on left side, forming a larger aperture (Fig. 4B ). All efferent branchial ducts are equal in length. VA consists of two SBAs and one medial section, bifurcating at approximately the third or fourth GP. First through third pairs of ABAs, which cannot be regarded as branches of the VA, branch from SBAs; however, fourth and fifth ABAs on left and right branch from the medial section of the ventral artery (Fig. 4B ). Ventral fin-fold weakly developed or vestigial, beginning approximately at middle of body and extending to cloaca (Fig. 3D ). Caudal fin-fold weakly developed, beginning posterior cloaca and extending around tail to dorsal surface.

Coloration when fresh: Body uniformly dark brown or purplish dorsally and white ventrally; white mid-dorsal line conspicuous, beginning from the upper region of the first prebranchial slime pore to around the tail. Eyespots conspicuous; whole barbels (rarely the tip) pale, and pale around mouth. Each gill aperture and pharyngocutaneous duct aperture with white margin; most slime pores blackish (except for tail region), tail slime pores same as surrounding color. White around cloaca; ventral fin-fold with a white line along the ventral midline; posterior margin of caudal fin pale (Fig. 2 ).

Coloration when preserved: Body brown to dark brown dorsally and murky white ventrally (more conspicuous than fresh specimen). Eyespots conspicuous; all slime pores surrounded by conspicuous white ring. Each gill aperture and pharyngocutaneous duct aperture conspicuous; ventral fin-fold pale; white mid-dorsal line inconspicuous.

Distribution.

Southwestern Sea of Korea.

Biology.

Attains a maximum TL of 292.0 mm (fresh specimen); this specimen is female, without mature eggs in the body cavity. A female specimen of 290.0 mm TL carries approximately 20 developing eggs, which have no terminal anchor filaments or hooks; each egg approximately 4-7 mm in diameter and 10-12 mm in length.

Etymology.

The specific name, wandoensis , refers to the type locality, in Korea.

Morphological comparisons

Eptatretus wandoensis sp. nov. is most similar to Eptatetus burgeri (Girard, 1855) and Eptatretus minor Fernholm & Hubbs, 1981 due to the presence of a light mid-dorsal line, gill apertures regularly spaced in a straight line, and EBDs of equal length. These three species differ from each other in the number of gill apertures (5 for E. wandoensis , compared to 6 for E. burgeri and E. minor ), body color (dark brown or purplish dorsally and white ventrally for E. wandoensis , compared to brown for E. burgeri and gray/brown pale for E. minor ), prebranchial slime pores (14-18 for E. wandoensis , compared to 18-23 for E. burgeri ), total slime pores (74-82 for E. wandoensis , compared to 81-92 for E. burgeri ), ventral fin-fold (weakly developed for E. wandoensis , compared to well developed for E. burgeri ), multicusps (3/2 for E. wandoensis , compared to 3/3 for E. minor ), total cusps (40-43 for E. wandoensis , compared to 46-52 for E. minor ) (Table 1 ), nasal-sinus papillae (absent for E. wandoensis , compared to paired for E. minor ), and eyespots (present for E. wandoensis , compared to absent for E. minor ). Eptatretus wandoensis sp. nov. can be distinguished from Eptatretus cheni (Shen & Tao, 1975), Eptatretus nelsoni (Kuo, Huang & Mok, 1994), and Eptatretus yangi (Teng, 1958) by the presence of regularly spaced gill apertures in a linear (vs. irregular and crowded for E. cheni , E. nelsoni , and E. yangi ) arrangement; equal length of all EBDs (vs. length of first efferent branchial duct notably longer than that of the most posterior efferent branchial duct); 40-43 total cusps (vs. 50-53 for E. cheni ; 32-40 for E. nelsoni and E. yangi ); 4 branchial slime pores (vs. no branchial slime pores); prebranchial length, 24.4%-26.3% of TL (vs. more than 29.0% of TL); branchial length, 5.2%-5.9% of TL (vs. less than 3.4% of TL); trunk length, 54.9-59.3% of TL (vs. less than 54.9%); eyespots conspicuous (vs. inconspicuous), and dorsal dark brown and ventral white body color (vs. brownish-grey). In comparison to Eptatretus species occurring in Korean and Japanese waters, this new species is well distinguished from the three most common hagfishes, Eptatretus atami (Dean, 1904), Eptatretus walkeri (McMillan & Wisner, 2004), and Eptatretus okinoseanus (Dean, 1904) based on the difference of gill apertures (5 in E. wandoensis sp. nov. vs. 6 in E. atami and E. walkeri vs. 8 in E. okinoseanus ), branchial slime pores (4, 0-1, 0, and 6-8), and a white mid-dorsal line (present, absent, absent, and absent) (Table 2 ).

Genetic comparisons

Differences among mtDNA sequences obtained from the holotype and paratypes of Eptatretus wandoensis sp. nov. were consistent with species-level divergences in other hagfish species ( Fernholm et al. 2013). The phylogenetic relationships of myxinid species, inferred from neighbor-joining trees, showed large genetic distances between similar hagfish species using mtDNA 16S rRNA (477 bp) and cytochrome c oxidase subunit I (COI) (466 bp) sequences. Eptatretus wandoensis sp. nov. is separated from other congeneric species by high genetic divergences of 0.9%-7.5% in 16S rRNA sequences and 4.9%-13.9% in COI sequences (Fig. 5 ). The respective genetic distances between this species and E. burgeri and E. minor were 0.9% and 4.5% in 16S rRNA sequences and 8.5% and 13.9% in COI sequences. In addition, phylogenetic analysis of 16S rRNA sequences showed that E. wandoensis sp. nov. is well separated from other five-gilled hagfishes ( E. cheni , E. nelsoni , and E. yangi ), with genetic differences of 7.5%, 1.4%, and 1.6%, respectively. Eptatretus cheni is located at a basal position of hagfishes and well nested in the Eptatretus clade.

Figures

Figure 1. Sampling location of Eptatretus wandoensis sp. nov. in Korea.

Figure 2. Overall view of Eptatretus wandoensis sp. nov., A holotype, PKU 62167, 292.0 mm in total length (TL) B paratype, PKU 62169, 202.0 mm TL C paratype, PKU 62171, 290.0 mm TL D paratype, PKU 62173, 275.0 mm TL, photographed prior to preservation. Scale bars: 1 mm.

Figure 3. Eptatretus wandoensis sp. nov. PKU 62167, prior to preservation A head dorsal view, white arrow indicates a white mid-dorsal line B head ventral view C gill apertures (GA) and pharyngocutaneous duct (PCD), note the location of GA and PCD D ventral view of body, black arrow indicates the ventral fin-fold (VFF) E dorsal region of body with a white mid-dorsal line.

Figure 4. Anatomical morphology of Eptatretus wandoensis sp. nov. PKU 62167. A palatine tooth, anterior unicusps (AUC) and posterior unicusps (PUC) B branchial region dissected, gill pouches (GP), median ventral aorta (MVA), separated ventral aorta (SVA), efferent branchial duct (EBD), pharyngocutaneous duct (PCD), dental muscle (DM), liver (L), and heart (H).

Figure 5. Phylogenetic tree of hagfishes based on mitochondrial DNA sequences, constructed with the Neighbor-joining (NJ) method using Kimura 2 - parameter distances A mitochondrial DNA 16 S rRNA sequences B mitochondrial DNA cytochrome c oxidase subunit I (COI) sequences. Numbers above tree branches are bootstrap values based on 1000 replicates. Scale bar represent nucleotide substitutions per site.