Garra cavernicola Freyhof, 2025, new species

Garra cavernicola, new species (Fig. 1–4) Holotype. NMW 100394 (443), 39 mm SL; Oman: Al-Hoota cave, main lake, 23,0844, 57.3571. Paratypes. NMW 100394, 3, 41–43 mm SL; NMW 100406, 2, 32–37 mm SL; same data as holotype. NMW 100321, 3, 39–42 mm SL; NMW 100408, 2, 47–58 mm SL; Oman: Al-Hoota cave, first lake, 23,0811, 57.3506. Diagnosis. Garra cavernicola is distinguished from other Garra occurring in the Hajar Mountains in Oman and the United Arab Emirates (G. barreimiae, G. gallagheri, G. longipinnis, G. shamal, G. sharq) by lacking an external eye (vs. present) and having a whitish or pink-coloured body without any pattern (vs. brown or grey, with a dark-brown or dark-grey mottled pattern). It is further distinguished from G. longipinnis by having smaller scales, and the absence of tubercles on the posterior portion of the scales (Esmaeili et al. 2025). Description. Morphometric data in Table 1. Body stout, moderately compressed laterally, more compressed along caudal peduncle. Dorsal head profile rising gently, straight or convex, interrupted by shallow hump from dorsal body profile in some individuals. Profile of back rising to about halfway between nape and dorsal-fin origin, gently convex until dorsal-fin origin. Ventral profile more or less straight to anal-fin origin. Head short and conical, with slightly convex interorbital distance. Snout blunt. No tubercles on head. Transverse lobe absent or very shallow, poorly demarcated posteriorly by transverse groove. Proboscis absent or very shallow. Eye externally absent, eye socket filled with fatty tissue. Barbels in two pairs; rostral barbel located antero-laterally, reaching to vertical of nares, or to base of maxillary barbel; maxillary barbel at corner of mouth, reaching vertical of eye socket. Rostral cap well-developed, with few grooves, papillate on ventral surface. Upper lip present as thin band without papillae. Upper jaw completely covered by rostral cap. Gular disc elliptical, longer than wide or as wide as long; narrower than head width through base of maxillary barbel; groove between antero-median fold and central callous-pad narrow and deep, papillae on latero-posterior flap small; anterior marginal surface of central callous pad with small papillae. Caudal fin with 9+8 branched rays; dorsal fin with 3 simple and 7½ branched rays, last simple ray slightly shorter than head length; distal margin straight or slightly convex; origin closer to caudal-fin base than to snout tip; inserted anterior to vertical through pelvic-fin origin; first branched ray longest, tip of last branched ray reaching vertical in front of anus. Pectoral fin with 1–2 simple and 13–15 branched rays, shorter than head length. Pelvic fin with 1 simple and 7–8 branched rays, not reaching to, or slightly beyond anus, not reaching anal-fin base, origin closer to anal-fin origin than to pectoral-fin origin, inserted below third or fourth branched dorsal-fin ray. Anal fin short, with 3 simple and 5½ branched rays; first branched ray longest; distal margin concave; origin closer to caudal-fin base than to pelvic-fin origin. Caudal fin forked; tip of lobes pointed; upper lobe longer than lower. Lateral line complete, or often incomplete on posterior part of flank, with 30–34 scales on body and 1–2 scales on caudal fin. Transverse scale rows above lateral line 4½; between lateral line and pelvic-fin origin 3½ and between lateral line and anal-fin origin 3½. Circumpeduncular scale rows 12, rarely 13 or 14. Predorsal scales deeply embedded, irregularly arranged, smaller flank scales. Chest without scales. One short axillary scale at pelvic-fin base, and 7–8, usually 7, scales between posteriormost pelvic-fin base and anus. Colouration. In life, body pink or whitish, fins whitish or usually transparent at distal and median parts; yellowish white in preservative. Distribution. Garra cavernicola is endemic to Oman, and is known only from the Al Hoota Cave and nearby Hoti Pit (Fig. 5). Etymology. The species name combines the Latin “caverna”, an underground chamber, and “cola”, meaning ‘inhabitant of’. A noun in apposition, indeclinable. Discussion This manuscript was first developed in 2023. Subsequently, Turner (2024) published a conceptually similar, yet more extensive paper on the topic, using G. cavernicola (as G. longipinnis) as an example. The ideas advanced by Turner (2024) strongly align with those discussed previously by Kottelat (1997), and further supported in the current paper. Despite this, the arguments made below are presented in their original form, as written before Turner (2024) was published, to illustrate how convergent these independent lines of thought are. Several fish species are believed to have long evolutionary histories in subterranean habitats as evidenced by their strong phylogenetic distinctness (Freyhof et al. 2016, Hashemzadeh Segherloo et al. 2016, Armbruster et al. 2016, Nguyen et al. 2021, Mao et al. 2021, Freyhof et al. 2022a, Raghavan et al. 2023). However, adaptation to subterranean environments can also occur relatively quickly as suggested by instances in which ancestors of some currently troglomorphic populations have invaded subterranean waters in geologically recent times. Close relationships between hypogean and epigean fishes imply that some cave fish populations may have originated following the Last Glacial Maximum (<10.000 years), as proposed for Garra (Kruckenhauser et al. 2011), Astyanax (Keene et al. 2015) and Barbatula (Behrmann-Godel et al. 2017). Among cave-adapted fishes, the genus Astyanax (specifically the blind, cave tetras) offers the most striking and best-studied examples. Historically, all subterranean populations of Astyanax were lumped into a separate genus Anoptichthys comprising a single species, A. jordani; while the epigean populations were assigned to the genus Astyanax. Romero & Paulson (2001) placed Anoptichthys in Astyanax and synonymised A. jordani with the epigean A. mexicanus. Strecker et al. (2004, 2012) suggested a more complicated evolutionary history, arguing that multiple independent invasions of cave systems by epigean Astyanax have taken place leading to several distinct, paraphyletic, subterranean populations. They found no significant gene flow between the cave populations and the surface fish, even when these co-occur syntopically. Elliott (2018) confirmed the findings of Strecker et al. (2004), and reported 31 caves known to be inhabited by the troglomorphic Astyanax, some related to epigean A. mexicanus, others to epigean A. aeneus. Interestingly, there were no attempts to revise the epigean-subterranean Astyanax complex from a taxonomic perspective, despite Strecker et al. (2012) demonstrating reproductive isolation in sympatry between different populations of this complex. There seems to be an implementation gap, and more work needs to be undertaken. Kullander (1999: 340) stated, “If the diagnostic characters are stable, and if both the epigean and the cave populations are self-perpetuating, then they are species distinct from each other, and all other species.”. It is clear from Strecker et al. (2004) that the subterranean populations are diagnosable and reproductively isolated. Still, their recognition as distinct species would make the ancestral epigean species (A. mexicanus) paraphyletic, and thus violate the criterion of monophyly under the ‘Phylogenetic Species Concept’ (PSC) (see Wheeler & Meier 2000 for different versions of the PSC). This might be why this issue has not yet been resolved, and the reason why most recent authors avoid using scientific names, and instead use the term “ Astyanax mexicanus complex” (Keene et al. 2015). A similar, though simpler situation has emerged in the case of Omani Garra longipinnis. Kruckenhauser et al. (2011) demonstrated that the subterranean population of G. longipinnis is not sister to all other populations, but rather nested within them, and showing close relation to the surface populations in the same region. Kirchner et al. (2017) investigated the subterranean Garra in Al Hoota Cave and nearby Hoti Pit, showing that while the cave population is isolated from the surface populations, individuals may occasionally be washed out into the surface habitats. These washed-out cave fish hybridise with epigean G. longipinnis, resulting in individuals with intermediate phenotypes, yet still being different from purely epigean fish. This clearly rejects the hypothesis by Banister (1984), that the cave population is just a phenotypic variation, and by this not based on own genetic mutation. However, Kirchner et al. (2017) observed the gene flow to be effectively unidirectional; the subterranean habitat remains off-limits to surface fish, preserving the genetic integrity of the cave population. Similar to the case of Astyanax mentioned above, recognising the subterranean population as distinct would make G. longipinnis —the ancestral epigean species, paraphyletic. Kirchner et al. (2020) lumped the two units that show distinct evolutionary trajectories into a single species as they do not differ based on the molecular markers applied. By this, they avoid the paraphyly of the parental species following PSC principles, where monophyly of all species is an essential criterion (Donoghue 1985, Cracraft 1989). Indeed, survival of the ancestral species and peripheral speciation is a long-debated issue (see Wiley, 1978, Kullander 1999) that has lost much of its attraction today. In many contemporary taxonomic practices, species are increasingly recognised only from molecular phylogenetic trees, and the monophyly of species has become a “dogma”, partly because phylogenetic trees offer a visually compelling demonstration whenever a species violates monophyly. Consequently, the ESC has often been sidelined, despite repeated cautionary advice (e.g., Mayden 1999). In doing so, ichthyology ignores the ESC as the primary species concept and, thus ignores the full diversity of sp