Opistognathus thionyi, Smith-Vaniz, William F., Tornabene, Luke & Macieira, Raphael M., 2018

Smith-Vaniz, William F., Tornabene, Luke & Macieira, Raphael M., 2018, Review of Brazilian jawfishes of the genus Opistognathus with descriptions of two new species (Teleostei, Opistognathidae), ZooKeys 794, pp. 95-133 : 99-104

Opistognathus thionyi sp. n. Figures 1, 2, 3, 4A, 5A, 7; Tables 1, 2, 3

Opistognathus sp.: Simon et al. 2013a: 2116, 2120 (undescribed species; listed and photograph); Pinheiro et al. 2015: 15, color fig. S. 38 (Dogaressa Seamount); Pinheiro et al. 2018: 10, Southwestern Atlantic (SWA) Endemic reef fishes - Annotated Checklist: 31.

Holotype.

CIUFES 2347, 45.4 mm SL, male, sandy rubble bottom at Praia do Lixo, Trindade Island, Brazil, 20°31'30"S, 29°19'20"W, 20 m, 20 February 2012, Thiony Simon and L.B.C. Xavier.

Paratypes.

(12 specimens 23.4-53.5 mm SL) all from Brazilian Province: MNRJ 51283 (1, 39.9*) and ZUEC 16914 (1, 44.9*), sandy rubble bottom at Praia do Lixo, Trindade Island, Brazil, 20°31'30"S, 29°19'20"W, 15 m, 18 February 2012, T. Simon and E.F. Mazzei; CIUFES 2344 (4, 23.4-32.7 & 32.5 C&S) and UF 239658 (1, 32.9), sandy rubble bottom at Praia do Lixo, Trindade Island, Brazil, 20°19'30"S, 29°19'20"W, 21 m, 21 February 2012, T. Simon and L.B.C. Xavier; AMNH 267140 (1, 32.5*), sandy rubble bottom at Praia do Lixo, Trindade Island, Brazil, 20°30'S, 29°20'W, 20 m, 20 February 2012, T. Simon and L.B.C. Xavier; CIUFES 2393 (1, 53.5), male, sandy rubble bottom at Portinho, Fernando de Noronha Archipelago, Brazil, 03°50'S, 32°24'W, 15 m, 11 July 2012, R.M. Macieira and H.T. Pinheiro; NPM 5029 (1, 38.4*), male, sandy rubble bottom at Enseada dos Portugueses, Trindade Island, Brazil, 20°31'30"S, 29°19'20"W, 25m, 8 August 2012, T. Simon and E.F. Mazzei; MZUSP 123868 (1, 30.9) and USNM 440401 (1, 35.3*), sandy rubble bottom at Praia do Lixo, Trindade Island, 20°31'30"S, 29°19'20"W, 17 m, 7 August 2012, T. Simon and L.B.C. Xavier.

Non-type material.

CIUFES 2054 (1, 27.5), sandy rubble bottom at Dogaressa seamount, Vitória-Trindade Chain, Brazil, 20°51'S, 33°40'W, 65 m, 12 April 2011, Expedição Cadeia Vitória-Trindade; CIUFES 2341-1 (1, 25.1), CIUFES 2341-2 (23.8) and CIUFES 2341-3 (1, 21.3), sandy rubble bottom at Praia do Lixo, Trindade Island, Brazil, 20°31'30"S, 29°19'20"W, 15 m, 18 February 2012, T. Simon and E.F. Mazzei; CIUFES 2346-3 (1, 29.2), sandy rubble bottom at Praia do Lixo, Trindade Island, Brazil, 20°31'30"S, 29°19'20"W, 20 m, 20 February 2012, T. Simon and L.B.C. Xavier.

Diagnosis.

A species of Opistognathus with the following combination of characters: anterior nostril a short tube with simple cirrus on posterior rim; maxilla rigid, not produced as a thin flexible lamina posteriorly; supramaxilla absent; subopercle with a broad, fan-like flap; vomer with 1 tooth; buccal area surrounding esophageal opening pale; body with 45-52 oblique body scale rows in longitudinal series; vertebrae 10+18; spinous dorsal fin with black blotch, when present, between spines 2-5. Body with five poorly defined irregular bands and sides sometimes with diagonal rows of pale spots smaller than eye diameter; when present, black blotch in spinous dorsal fin between spines 2-5; buccal area surrounding esophageal opening pale. This species is also easily distinguished from congeners by divergence in the mitochondrial gene COI, as specimens form a monophyletic group that differs from its closest relative ( O. maxillosus ) by an average of 9% (654 bp analyzed).

Description.

Morphometric data are given in Table 3 for the holotype and specimens indicated above by an asterisk; other comparative features are presented in Table 1. Where counts differ, those of the holotype are given first, followed in parentheses by those of the paratypes. Dorsal fin XI, 15 (15-16). Anal fin III, 15 (14-15, usually 15). Pectoral-fin rays 20 (19-20). Vertebrae: 10+18, last pleural rib on vertebra 10, epineurals 13-15. Supraneurals absent. Caudal fin: procurrent rays 5+5 (4-6+4-5); segmented rays 8+8, middle 12 branched, total elements 26 (24-26); hypural 5 absent. Gill rakers (number not increasing with increase in SL in adults) 9+19 (8 –11+17–20=25– 31).

Scales absent from head, nape, pectoral-fin base and breast; belly completely scaled, and sides fully scaled except for area above lateral line anteriorly. Body with 48 (45-52) oblique scale rows in longitudinal series. Lateral-line terminus below verticals between segmented dorsal-fin ray 3 (3-5). Anterior lateral-line pores relatively numerous and arranged in branched series along lateral-line tubes, all of which are embedded in skin. Mandibulo-preopercular pore positions all consisting of multiple pore series, except first two mandibular pore positions occupied by simple pores. Infraorbital pore positions consisting of multiple series that extend onto cheeks. Nape nearly to completely covered by sensory pores except for V-shaped naked area immediately in front of dorsal-fin origin (Figure 4A).

Anterior nostril positioned closer to posterior nostril than to dorsal margin of upper lip, and adults with a rounded cirrus that usually reaches anterior margin of orbit when depressed; height of cirrus 2.0-3.0 times maximum diameter of posterior nostril. Dorsal fin moderately low anteriorly, with posterior rays slightly longer; profile relatively uniform without noticeable change in fin height at junction of spinous and segmented rays. Dorsal-fin spines stiff and straight with pungent tips and in larger specimens the skin covered tips usually with pale, slightly swollen fleshy tabs. Segmented dorsal- and anal-fin rays all typically branched distally. Outermost segmented pelvic-fin ray not tightly bound to adjacent ray and interradial membrane strongly incised distally; tip of depressed pelvic fin in front of anal-fin origin. Upper margin of subopercle consisting of a broad, truncated flap (Figure 4A) and dorsalmost spine of opercle not noticeably elongate; posterior margin of preopercle distinct, with a well-developed groove dorsally. No papillae on inner surface of lips. Fifth cranial nerve passes over A1β section of adductor mandibulae muscle.

Upper jaw not sexually dimorphic, extending 0.45 (0.3-0.6) eye diameters behind orbit in specimens 32.5-53.5 mm SL; posterior end of maxilla rigid and truncate, without a thin flexible lamina; supramaxilla absent. Coronoid (ascending) process of articular slightly tilted backward and somewhat club-shaped with anterodorsal end bluntly pointed and posteroventral end bluntly rounded (Figure 5A). Premaxilla anteriorly with an outer row of stout teeth and an inner row of smaller, backward slanting teeth, some nearly horizontal; laterally teeth uniserial and becoming progressively smaller and more closely spaced. Dentary anteriorly with an outer row of stout teeth and an inner row of smaller, backward slanting teeth; laterally teeth uniserial and smaller but not progressively so. Vomer with 1 large tooth. Infraorbital bones tubular, with numerous openings for sensory canals; third infraorbital with a wide suborbital shelf. Postcleithra consisting of two well separated bones; dorsal postcleithrum an irregular elongate oval, narrowest ventrally, ventral postcleithrum rod-shaped with pointed ends.

Color in life (Figures 1, 2). Body coloration chestnut brown to dark brown with five very irregular and poor defined dark bands that extend onto base of dorsal fin; head sometimes with pale speckles on posterior half; upper jaw with a wide white band near posterior end; eyes reddish brown sometimes with narrow pale radiating bands; lips with alternating dark and pale bands; branchiostegal membranes dark, especially in mature males; dorsal fin light yellow sometimes with diagonal rows of pale spots and a black blotch, when present, between spines 2-5; anal fin with small pale spots; pelvic fins dark; pectoral fins speckled and a large white spot on pectoral-fin base; caudal fin with pair of pale basicaudal spots and fin rays with prominent black speckles or narrow bands.

Preserved color (Figure 3). As above except with white, brown, and black markings. Inner margin of maxilla posteriorly and adjacent membranes with dusky blotch. Buccal area surrounding esophageal opening pale.

Comparisons.

The Caribbean allopatric Opistognathus maxillosus Poey, 1860 shares with O. thionyi the same subopercle shape but in addition to having more longitudinal body scale rows (69-85 vs. 45-52), the dark spot in the dorsal fin is always between spines 6-9 (vs. when present between spines 2-5), and the buccal area immediately surrounding the esophageal opening very dark (vs. pale). An updated description of Opistognathus maxillosus is given in Smith-Vaniz (1997). The only other species of Opistognathus with a broad, fan-like subopercle are the eastern Pacific O. galapagensis Allen & Robertson, 1991 and O. fossoris Bussing & Lavenberg, 2003. In addition to other characters discussed by Bussing and Lavenberg (2003), both species differ from O. thionyi most notably in having the posterior end of maxilla ending as thin, flexible lamina (vs. end of maxilla rigid), more body longitudinal scale rows, 83-105 (vs. 45-52), most of nape immediately in front of dorsal-fin origin without cephalic pores (vs. almost completely covered with pores), and in having very different color patterns. Comparison of the six species of Opistognathus known from the Brazilian Province is given in Table 1.

Etymology.

The specific name honors our colleague and dear friend Thiony Simon (1985-2016), who passed away during preparation of this article. He collected most of the type material of the new species and dedicated his life to study and conservation of Brazilian reef ecosystems.

Distribution, habitat, and natural history.

Opistognathus thionyi is known only from three oceanic sites, Trindade Island, Dogaressa Seamount, and Fernando de Noronha Archipelago (Figure 6), and is an endemic species of the Brazilian Province (sensu Briggs and Bowen 2012 and Pinheiro et al. 2018). This species is possibly broadly distributed along the coast on the outer shelf, an area that is virtually unsampled. It has been recorded from 10-65 m, and found solitarily, always in small constructed burrows on sandy rubble bottoms (Figure 7). It feeds on small benthic organisms that live near the bottom (e.g., small shrimps).

Conservation.

The conservation status of Opistognathus thionyi (cited as Opistognathus maxillosus Poey, 1860 - unpublished data) has been assessed by the Ministério do Meio Ambiente/Instituto Chico Mendes de Conservação da Biodiversidade (MMA/ICMBio - Brazil) and listed as Least Concern. However, anthropogenic activities on oceanic marine ecosystems (i.e., seamount mining, fisheries, marine traffic, tourism, and human occupation of the islands), and the inadequate protection from these impacts currently provided by new Brazilian marine protected areas in the Vitória-Trindade Seamounts Chain (see Brasil 2018; Giglio et al. 2018; Magris and Pressey 2018), could threat the existence of Thiony’s jawfish in that part of its range in the near future.