Gymnothorax poikilospilus Chen & Huang, 2022

Huang, Wen-Chien, Loh, Kar-Hoe & Chen, Hong-Ming, 2022, Gymnothorax poikilospilus, a new moray eel (Teleostei: Anguilliformes: Muraenidae) from Penghu Islands, western Taiwan, Zootaxa 5189 (1), pp. 87-102 : 88-97

Gymnothorax poikilospilus Chen & Huang , sp. nov.

Common name: Variegated moray eel

( Figs. 1 , 2 )

urn:lsid:zoobank.org:act:855F9025-193E-4B0E-9118-C217166CDADF

Holotype. TOU-AE 0645, 768 mm TL, female, off Hsiao-men fishing harbor (23°39'N, 119°29'E), Xi-yu Township, Penghu Islands, Taiwan, ca. 10–20 m depth, trap of PVC tube, 10 June 2002, coll. Captain Ping Hong.

Paratype. TOU-AE 5112, 868+ mm TL, tail tip lost, female, collected with the holotype.

Diagnosis. A medium-sized moray with typical muraenid shape, anus at mid-point of body. Dorsal fin high. Eyes above mid-jaw. Jaws slightly arched and can’t completely close. Cephalic sensory pores small. Teeth uniserial, slender and pointed. Body brown or gray-brown with several rows of large dark brown patches on back of body and dorsal fin. Patches obscure during daytime and becoming obvious at night. Dorsal head dark brown and spotless. Fins with fine greyish-white margins when alive but invisible in preservation. Inner skin of nostrils and head pores whitish. Oral cavity uniform brown. Throat grooves darkish. Iris of the eye reddish-brown. Predorsal vertebrae 4, preanal vertebrae 57–59, total vertebrae 141.

Description. Proportions in percent of TL for holotype: tail length 50.3, trunk length 34.8, head length 14.5, depth at gill opening 8.3, depth at anus 7.2. Proportions in percent of HL for holotype (paratype): predorsal length 60.0 (58.0), length of upper jaw 46.3 (47.8), length of lower jaw 46.8 (47.7), interorbital width 11.1 (11.7), snout length 17.9 (18.5), eye diameter 8.7 (8.3). Predorsal vertebrae 4 (4), preanal vertebrae 57 (59), total vertebrae 141 (137+) ( Table 1 ).

A medium-sized moray with typical muraenid shape, body stout, anus at mid-point of body. Dorsal fin high, originating anterior to gill opening. Anal fin shallow, its origin immediately behind anus. Gill opening slightly below lateral midline, opening as a hole, about size of eye in diameter. Eyes above mid-jaw. Jaws slightly arched and can’t completely close, teeth visible when mouth closed, jaws subequal in length. Snout acute and moderately elongate. Anterior nostril at tip of snout, as short tube shorter than eye radius in length, without folds on the anterior tip. Posterior nostril above and slightly anterior to front margin of eye, as an oval pore with raised rim.

Cephalic sensory pores small, their number within range of typical muraenids ( Fig. 3 ). Three supraorbital pores, first at tip of snout below level of anterior nostril; second immediately above base of anterior nostril; third along margin of snout above level of horizontal middle line of eye. Four infraorbital pores, first immediately below and posterior to anterior nostril base; second about at anterior one-third of distance between anterior nostril base and anterior margin of eye, slightly posterior to third supraorbital pore in horizontal; third below anterior margin of eye; fourth below posterior margin of eye. Six preoperculo-mandibular pores along lower jaw before corner of mouth; in holotype, pores arranging differently between left and right jaws but amounting the same number ( Fig. 4 ). Two branchial pores on posterior-dorsal head, posterior to dorsal-fin origin and anterior to gill opening.

Teeth slender and pointed, slightly retrorse, edge without serration ( Fig. 4 ). Peripheral intermaxillary teeth uniserial, 6 (6–9) large canines on each side with small teeth in intervals; teeth becoming larger posteriorly. Median intermaxillary teeth uniserial, with 3 (3) tall and spaced teeth, second tooth longest. Maxillary teeth uniserial, with 18–19 (20) triangular and recurved teeth on each side, anterior most 1–2 teeth very small, following by 2–4 sharply increase-sized teeth flanked by several tiny teeth; remaining teeth gradually decreasing in size, smallest at posterior end. Vomerine teeth almost invisible, only one very small and stout tooth left in holotype, with four sockets of missing teeth. No visible vomerine teeth in paratype. Dentary teeth uniserial, with 27 (30–31) teeth on each side, anterior most 5–7 teeth obviously larger and flanked by some tiny teeth; size of remaining teeth subequal centrally and becoming much smaller at posterior end.

Body brown or gray-brown in ground color, with several rows of inconspicuous large dark brown patches on back of body and dorsal fin. Ventral parts of head and trunk slightly lighter. Dorsal head dark brown without blotch. Throat grooves darkish. Inner skin of nostrils and head pores whitish. Color of oral cavity similar to head. Iris of the eye reddish-brown. Body color variable when alive. During daytime, body almost uniform brown, dark patches obscure; during nighttime, ground color turning lighter and dark patches becoming obvious ( Fig. 5 ), fins with fine greyish-white margins ( Fig. 6 ). Preserved color similar to fresh, pale margins of fins and dark patches nearly invisible.

Distribution. Currently only known from the type locality Penghu Islands.

Biology. From 10 June 2002, we had reared the holotype in our laboratory's aquarium until 4 February 2005, it accidentally crawled out of the aquarium at night and died. We dissected the holotype and found that there were many mature eggs in its abdominal cavity ( Fig. 7 ). The mature eggs were between 0.8–1.2 mm in diameter, and the batch fecundity was about 20,000 eggs. Under microscope observation, there was the other immature egg group in its ovaries, the diameters of oocytes were about 0.15–0.26 mm.

We also reared the paratype until its death on 22 September 2008. Under the microscope, its gonads belonged to immature ovaries, and there were 2 groups of oocytes with different egg diameter interval ranges: the larger group was 0.17–0.26 mm, and the smaller group was 0.07–0.13 mm. We fed these two specimens with fish and squid meat.

Etymology. The specific name is from the Greek poikilo (varied, variegated) and the Greek spilos (a spot, stain), in reference to its varied body markings between daytime and nighttime.

COI analyses. After alignment and trimming, 612 bp of COI sequences were left for analyses. The topology of ML tree reveals that each species is positioned in a monophyletic clade and separated from others ( Fig. 8 ). The genus Enchelycore is not monophyletic, conforming with previous studies based on different mitochondrial genes ( Tang & Fielitz 2013; Smith et al. 2019). The inter- and intra-species K2P genetic distances are 9.8–22.5% and 0.1–0.7%, respectively ( Table 2 ). Gymnothorax poikilospilus is most closely related to E. schismatorhynchus , however, with an 11.4% K2P distance which far exceeds the general intraspecific variation of moray eels ( Huang et al. 2018), confirming its validity.

Remarks. Although the new species has arched jaws that can’t close completely, it is placed under the genus Gymnothorax instead of Enchelycore according to the following reasons: (1) the extents of elongation and arching of its jaws are much lower than species of the genus Enchelycore ( Fig. 9 ); (2) its maxillary and dentary teeth are uniserial (vs. mostly biserial in Enchelycore ). While hard to quantify the extent of elongated and arched jaws in Enchelycore , this characteristic could further reflect on the narrowing of the anterior part of head, including the interorbital width. According to our unpublished data, the interorbital width of Enchelycore ranges from 7.8–10.4% of HL (based on one E. bayeri , two E. lichenosa , two E. pardalis , and four E. schismatorhynchus ), comparing to>10% of HL in most species of Gymnothorax . The new species has an interorbital width of 11.1–11.7% of HL which is completely within the range of Gymnothorax . In addition, arched jaws can also be found in several non- Enchelycore species, such as Enchelynassa canina and Gymnothorax eurostus , suggesting it might not be an appropriate diagnostic characteristic. On the other hand, we found that the largest examined Enchelycore schismatorhynchus (949 mm TL) has much fewer maxillary and dentary teeth compared to smaller specimens (510–642 mm TL) (maxillary teeth 15–17 vs. 29–31; dentary teeth 28–29 vs. 37–44), and all series of its teeth are arranged in single rows (vs. biserial of maxillary and dentary teeth in smaller specimens). Considering ambiguous morphological characters and the genetically non-monophyly of the genus Enchelycore , we temporarily designate the new species under the genus Gymnothorax . Further systematic research is needed to verify the validity of Enchelycore .

Gymnothorax poikilospilus is morphologically most similar to Enchelycore schismatorhynchus , G. monochrous , and G. pseudothyrsoideus , three sympatric morays that possess gray-brown body color and pale margins on fins ( Fig. 10 ). It differs from E. schismatorhynchus by the wider interorbital width (11.1–11.7% vs. 8.9–10.4% of HL), fewer predorsal (4 vs. 5–6) and preanal vertebrae (57–59 vs. 61–63), and the color of the tip of anterior nostrils (uniform brown vs. dark brown). It can be distinguished from G. monochrous by more dentary teeth (27–31 vs.16–25), and more total vertebrae (141 vs. 130–138). Lastly, G. poikilospilus is different from G. pseudothyrsoideus by having more maxillary (18–20 vs. 11–17) and dentary teeth (27–31 vs. 19–24), and more total vertebrae (141 vs. 130–135). Aside from morphometric and meristic characters, the obviously arched jaws make G. poikilospilus unique when compared with G. monochrous and G. pseudothyrsoideus ; and the lack of the prominent white fin margin makes G. poikilospilus distinguishable at a glance when side by side with E. schismatorhynchus ( Fig. 10 ). Furthermore, the pale fin margins of the three similar species are still visible in preservation while completely disappearing in G. poikilospilus .

Gymnothorax poikilospilus can be excluded from the four synonyms of E. schismatorhynchus ( Eurymyctera crudelis Kaup, 1856 , Muraena congeroides Bleeker,1860 , Muraena hemprichii Klunzinger, 1871 , and Rhinamuraena eritima Jordan & Seale, 1906) by the dentition (uniserial vs. biserial maxillary and dentary teeth) and the color of fin margin (brown vs. white); and be excluded from the only synonym of G. pseudothyrsoideus , Gymnothorax makassariensis Bleeker, 1863 , by more maxillary teeth (18–20 vs. 14–15) and more dentary teeth (27–31 vs. 20–23) ( Böhlke & Smith 2002).

Gymnothorax poikilospilus can be easily distinguished from other three similar species of Gymnothorax by having more outer maxillary teeth (18–20 vs. 10–18 in G. cinerascens , 9–16 in G. hepaticus , and 11–16 in G. longinquus ), more outer dentary teeth (27–31 vs. 12–22, 12–21, and 18–22), and more total vertebrae (141 vs. 128–135, 128–132, and 128–134) ( Smith et al. 2019; Huang et al. 2020). It can also be simply separated from the three Indo-Pacific jaw-arched brown morays (viz. Enchelycore bayeri , Enchelycore bikiniensis , and Enchelynassa canina ) by using a single characteristic of uniserial maxillary and dentary teeth (vs. biserial in other three species) ( Böhlke & Smith 2002; Loh et al. 2012; Smith et al. 2019).

Comparative materials. Enchelycore schismatorhynchus . four specimens, 510–949 mm TL. Taiwan: DOS 07936 (1, 510 mm), Changbin , Taitung ; DOS 08729 (1, 949 mm), Chenggong , Taitung ; NMMB-P007074 (1, 642 mm), Checheng , Pingtung ; NMMB-P015637 (1, 640 mm), Liuqiu , Pingtung . Gymnothorax monochrous . seven specimens, 557–891 mm TL. Philippines: DOS 06828 (4, 557– 784 mm), Bogo , Cebu . Taiwan: DOS 06376 (1, 758 mm), Donggang , Pingtung ; DOS 07127 (1, 891 mm), DOS 08281 (1, 666 mm), Magong , Penghu Islands. Gymnothorax pseudothyrsoideus . five specimens, 400–876 mm TL. Taiwan: DOS 07943 (3, 564– 876 mm), Eziliao , Kaohsiung ; DOS 08038 (1, 635 mm), Qianzhen , Kaohsiung ; DOS 08076 (1, 400 mm), Datan , Taoyuan .

Figures

FIGURE 1. Gymnothorax poikilospilus sp. nov., holotype, TOU-AE 0645, 768 mm TL.

FIGURE 2. Gymnothorax poikilospilus sp. nov., paratype, TOU-AE 5112, 868+ mm TL.

FIGURE 3. Drawing of the head showing the distribution pattern of cephalic sensory pores of Gymnothorax poikilospilus sp. nov., holotype, TOU-AE 0645.

FIGURE 4. Dentition of Gymnothorax poikilospilus sp. nov., holotype, TOU-AE 0645. Upper jaw (left) and lower jaw (right). Dotted lines represent the sockets of missing teeth.

FIGURE 5. Live coloration of Gymnothorax poikilospilus sp. nov., holotype, TOU-AE 0645. (A) daytime; (B) nighttime.

FIGURE 6. Live coloration of Gymnothorax poikilospilus sp. nov.. (A) daytime, paratype, TOU-AE 5112; (B) nighttime, front, paratype, TOU-AE 5112; behind, holotype, TOU-AE 0645, showing the obvious dark patches and fine greyish-white fin margins.

FIGURE 7. Mature ovaries of Gymnothorax poikilospilus sp. nov., holotype, TOU-AE 0645.

FIGURE 8. The maximum likelihood tree based on COI sequences (612 bp) with Uropterygius macrocephalus and U. micropterus as outgroups. Numerals beside the internal branches are bootstrap values which are only shown for main branches, and values below 50 are excluded. Labels after scientific names are GenBank accession numbers, voucher numbers, and collection locations.

FIGURE 9. Radiography showing the skeletal structure of the head region. (A) Enchelycore schismatorhynchus, NMMB- P015637, 640 mm TL; (B) Gymnothorax poikilospilus sp. nov., holotype, TOU-AE 0645, 768 mm TL; (C) G. monochrous, DOS 06828-1, 734 mm TL.

FIGURE 10. (A) Gymnothorax poikilospilus sp. nov., holotype, TOU-AE 0645, 768 mm TL; and three morphologically most similar species: (B) Enchelycore schismatorhynchus, DOS 08729, 949 mm TL; (C) G. monochrous, DOS 06828-1, 734 mm TL; and (D) G. pseudothyrsoideus, DOS 07943-1, 876 mm TL.