No longer a circumtropical species: revision of the lizardfishes in the Trachinocephalus myops species complex, with description of a new species from the Marquesas Islands

Abstract

Trachinocephalus, a formerly monotypic and nearly circumtropical genus of lizardfishes, is split into three valid species. Trachinocephalus gauguini n. sp. is described from the Marquesas Islands and is distinguished from the two other species in the genus by having a shorter snout, a narrower interorbital space, larger eye and modally fewer anal-fin and pectoral-fin rays. The distribution of Trachinocephalus myops (type species) is restricted to the Atlantic Ocean and the name Trachinocephalus trachinus is resurrected for populations from the Indo-West Pacific Ocean. Principal component analyses and bivariate plots based on the morphometric data differentiated T. gauguini from the other two species, but a substantial overlap between T. myops and T. trachinus exists. Phylogenetic evidence based on mtDNA COI sequences unambiguously supports the recognition of at least three species in Trachinocephalus, revealing deep divergences between the Atlantic Ocean, Indo-West Pacific Ocean and Marquesas entities. Additional analyses of species delimitations using the generalized mixed Yule coalescent model and the Poisson tree processes model provide a more liberal assessment of species in Trachinocephalus, indicating that many more cryptic species may exist. Finally, a taxonomic key to identify the three species recognized here is provided.

First record of Gauguin's blunt-nose lizardfish, Trachinocephalus gauguini Polanco, Acero & Betancur 2016 (Teleostei: Synodontidae) outside the Marquesas Archipelago

“…Morphometric data and meristic data for the two Papua New Guinea specimens are as in Table 1 and 2 respectively. The morphological characteristics fit within the range of the identification key, description of body color pattern, and photographs provided in Polanco et al (2016): L Sn 6.7-10.0% of HL, L Sn 12.6-18.9% of D B , L Sn 31.6-51.7% of D E , W I 4.0-6.7% of HL; pectoral fin rays 11, anal fin rays 14-16; pectoral, caudal and anal fin yellow; dorsal fin dark yellow; four obvious yellow stripes along the body longitudinally, with several inconspicuous vertical bars across; an oval black spot above the dorsal border of the operculum, and a rather wide dark blotch below the eye (indistinct in NTUM 11212) (Fig. 1A, B).…”

“…NTUM 11201 (tissue voucher: PNG 3126), specimen collected from the same site as T. gauguini, NTUM 11085 (see above). Polanco et al (2016) is included for comparison. Standard lengths (SL) and head lengths (HL) are given in mm.…”

“…All measurements were taken in a straight line, made with a dial caliper and recorded to the nearest 0.1 mm. For each specimen, 21 measurements and five counts were recorded, following Polanco et al (2016). The examined specimens were deposited at the ichthyological collection of the National Taiwan University Museums, Taipei (NTUM) under registration nos: NTUM 11201 (tissue voucher PNG 3126), NTUM 11085 (tissue voucher PNG 3127), and NTUM 11212 (tissue voucher PNG 3163).…”

“…The genus was previously regarded as monotypic, containing only a single species, Trachinocephalus myops (Forster 1801), with nearly circum-tropical and subtropical distribution (Briggs 1960). However, a recent taxonomic revision (Polanco et al 2016) based on morphological and molecular evidence, challenged this traditional classification and recognized three valid species, including a newly described species, T. gauguini Polanco, Acero & Betancur 2016, found exclusively in French Polynesian waters around the Marquesas Islands in the western Pacific. The other two congeneric species, T. myops and T. trachinus (Temminck & Schlegel 1846), recognized by Polanco et al (2016) have much wider distribution ranges in the Atlantic and the Indo-West Pacific Oceans (except the Marquesas), respectively.…”

“…The other two congeneric species, T. myops and T. trachinus (Temminck & Schlegel 1846), recognized by Polanco et al (2016) have much wider distribution ranges in the Atlantic and the Indo-West Pacific Oceans (except the Marquesas), respectively. The three species are currently known to be allopatrically distributed (Polanco et al 2016).…”