First record of the Kermadec Clingfish, Flexor incus Conway, Stewart & Summers, 2018 (Gobiesocidae), from New Caledonia and Australia

Two specimens (17.1 and 29.1 mm standard length) of Flexor incus Conway, Stewart & Summers, 2018 (Gobiesocidae) were collected from New Caledonia and Lord Howe Island, Australia. The species and genus were originally described on the basis of 15 specimens from the Kermadec Islands, New Zealand, where the genus has been considered endemic. The two specimens reported herein represent the first records of F. incus from New Caledonia and Australia.


Introduction
The family Gobiesocidae is a moderate-sized fish family, commonly called clingfishes because all members of the family, except for the shore eel genus Alabes Cloquet, 1816, have a well-developed ventral adhesive disk with which they adhere tightly to the substrate (Briggs 1955;Conway et al. 2020). Most members of the family inhabit intertidal and subtidal zones in the Atlantic and Indo-Pacific oceans, and a small number of species occur in deeper waters down to 570 m or in freshwater streams in the neotropics (Briggs 1955;Conway et al. 2017a;Hastings and Conway 2017). Currently, the family contains 185 valid species of 51 genera (Fricke et al. 2021). However, taxonomic study on the family continues to result in the description of new taxa (four new genera and 22 new species have been described since 2015) (Fricke et al. 2021).
As part of an ongoing taxonomic study of the Gobiesocidae, we examined unidentified material from New Caledonia and Australia (Lord Howe Island) held in the ichthyology collections of the National Museum of Natural History (Washington, DC) and the Australian Museum (Sydney), respectively. Subsequently, these specimens were identified as Flexor incus Conway, Stewart & Summers, 2018, originally described as a new genus and species on the basis of 15 specimens from the Kermadec Islands, New Zealand. Because additional specimens of the species have not been recorded until now, the present specimens, reported in this study, represent a significant distribution range extension for F. incus into the southwestern Pacific Ocean. Comparative comments on Flexor and the similar, potentially closely related genera Pherallodus and Propherallodus are also provided.

Results
New records ( Identification. Morphometrics data on the two specimens from New Caledonia and Australia (Fig. 2) are provided in Table 1. The present specimens agree closely with Conway et al. (2018a), the original description of F. incus, in having the following characters: 9 or 10 dorsalfin rays; 9 anal-fin rays (except for USNM 322448); 24 pectoral-fin rays (except for AMS I. 17424-003); upperjaw teeth incisiviform, compressed laterally, with hooklike tips strongly curved posteriorly (ca. 90°), except for symphysis with 2 or 3 slightly curved conical teeth; lower-jaw teeth with pointed conical tips, inner surface slightly curved; small oval opening between premaxillae present; head sensory canal pores well developed, including 2 nasal, 2 lacrimal, 2 postorbital, and 3 preopercular pores; mandibular pores absent; gill membranes free from isthmus; pelvic fins and pectoral-girdle elements forming a circular, "double" adhesive disc; disc regions A, B, and C with flattened papillae (damaged in AMS I. 17424-003), anterior part of disc region A with 3 rows of papillae across center, disc region B with 4 rows of papillae, and disc region D without papillae (Fig. 3).
Counts of anal-and pectoral-fin rays differ slightly between the specimens presented herein and those of the type series [7 anal-fin rays (USNM 322448) and 22 pectoral-fin rays (AMS I. 17424-003) vs. 8 or 9 and 24 or 25, respectively in the original description]. However, these differences are regarded here as intraspecific variations of F. incus as similar variations have been reported  in other gobiesocid genera (e.g., Aspasma ubauo Fujiwara and Motomura 2019). In addition, Conway et al.
(2018a) described 2 or 3 rows of papillae on disc region C whereas only a single row of papillae was confirmed in USNM 322448 (Fig. 3). This discrepancy may be related to papillae loss, which can occur easily during collection leaving no trace (Fujiwara and Motomura 2018a).

Discussion
Flexor incus was described as a new genus and species on the basis of 15 specimens from the Kermadec Islands of New Zealand. In the original description (Conway et al. 2018a), F. incus was reported from only two islands within the Kermadec archipelago, including Raoul Island (type locality) and L'Esperance Rock, and no additional records of the species have been reported until now. The specimens reported herein, collected from Loyalty Islands and Lord Howe Island, represent the first records of F. incus from New Caledonia and Australia, respectively. This suggests that the species possibly has a wider distribution in the southwestern Pacific Ocean and Tasman Sea (Fig. 1). Interestingly, except for the deep-water clingfish Kopua nuimata Hardy, 1984, all tidal and subtidal species of clingfishes inhabiting the main islands of New Zealand (12 species representing 8 genera) are endemic to this region (Stewart 2015;Conway et al. 2017bConway et al. , 2018bFujiwara and Motomura 2020).
Although the Kermadec Islands are included in New Zealand waters, these islands are located far from the relatively well-surveyed main islands and it is unlikely that F. incus is present beyond the Kermadec Islands in New Zealand waters.
In their original description of F. incus, Conway et al. (2018a) pointed out that the higher classification of clingfishes proposed by Briggs (1955) may require revision. More recently, the classification scheme of Briggs (1955) was revised by Conway et al. (2020), who recognized nine subfamilies in the Gobiesocidae based on the results of a molecular phylogenetic investigation. According to them, the monotypic genus Flexor is assigned to the subfamily Diademichthyinae, which they expanded to include several additional genera formerly included in the Aspasminae, Diplocrepinae, and Protogobiesocinae by Briggs (1955) and Fricke et al. (2016). Although Flexor was recovered as the sister taxon to Aspasmichthys ciconiae (Jordan & Fowler, 1902) (Briggs, 1955)]. These three genera can be distinguished from other members of the Diademichthyinae sensu Conway et al. (2020) in having a "double" adhesive disc (sensu Briggs 1955) and gill membranes free from the isthmus. Flexor differs from Pherallodus and Propherallodus by the teeth shape in both jaws, disc papillae (also see below), and head sensory canal pores (see Conway et al. 2018a: 95). Papillae are present across the center of region A and C in Flexor ( Fig. 3; Conway et al. 2018a: fig. 9A) whereas papillae are said to be absent from the center of both region A and C in Pherallodus (Shiogaki and Dotsu 1983). Examination of specimens of Pherallodus indicus in this study confirmed the absence of papillae from the center of region A as described by Shiogaki and Dotsu (1983) but papillae are present at the center of region C, as in Flexor. Compared with Pherallodus and Propherallodus, Flexor exhibits fewer rows of papillae on disc region B [4 or 5 rows in Flexor ( Fig. 3; Conway et al. (2018a) vs. 5-7 (usually 6) in Pherallodus and Propherallodus (Shiogaki and Dotsu 1983;Fujiwara and Motomura 2018b;this study].