Acentronura breviperula Fraser-Brunner and Whitley, 1949

Short, Graham A. & Trnski, Thomas, 2021, A New Genus and Species of Pygmy Pipehorse from Taitokerau Northland, Aotearoa New Zealand, with a Redescription of Acentronura Kaup, 1853 and Idiotropiscis Whitley, 1947 (Teleostei, Syngnathidae), Ichthyology & Herpetology 109 (3), pp. 806-835 : 818

Acentronura breviperula Fraser-Brunner and Whitley, 1949

Figures 8A , 9A , 10A , 11A ; Tables 2–4

Acentronura breviperula Fraser-Brunner and Whitley, 1949: 148 , fig. 1 (Mabuiag, Torres Strait, Queensland).

Diagnosis.— See generic diagnosis. Acentronura breviperula differs from its congeners by the following combination of characters: supraoccipital consisting of a distinct bony bipartite dorsomedial crest, segments arcuate in lateral view, followed by an elevated and long bony dimple; posterior margin of second segment of dorsomedial crest merging within the bony dimple, which is approximately one-third longer than the dorsomedial crest and tapered posteriorly.

Description.— Morphometric and meristic characters listed in Tables 2–4 . Superior trunk and tail ridges discontinuous below dorsal-fin base, lateral tail ridge present, inferior trunk ridge ends at anal ring, lateral trunk ridge confluent with inferior tail ridge. Head angled ventrally 25° from the principal body axis, the anterodorsal profile slightly conoid in lateral aspect; supraoccipital low, not elevated, with a distinct bony bipartite dorsomedial crest, segments arcuate in lateral view, followed by an elevated and long bony dimple; posterior margin of second segment of dorsomedial crest merging within the bony dimple, which is approximately one-third longer than the dorsomedial crest and tapered posteriorly; bilateral bony lobed protuberances on the posterolateral margins of the post-temporal bones ( Fig. 10A ); anterior nuchal plate absent ( Fig. 9A ); posterior nuchal plate present anterior to cleithrum with dorsomedial crestlike ridge along its dorsum, large gap between the supraoccipital and posterior nuchal plate; small blunt spine midway between orbit and lobed protuberance on operculum; cleithral ring distinct, discontinuous mid-dorsally; gill slit between supraoccipital and cleithral ridge; rim of orbit projecting dorsolaterally and slightly ventrolaterally; snout spine absent; interorbital narrow, depressed; opercular ridge distinct, entire, angled dorsally toward gill opening; swelling of gular region ventroposterior to orbit absent; pectoral-fin base without distinct ridges, low, strongly elevated ventrolateral bulge supporting the pectoral-fin absent; trunk deepest anteriorly, principal body ridges distinct; principal body ridge spines absent; caudal fin absent. Acentronura breviperula exhibits strong sexual dimorphism associated with the presence of a brood pouch. The brood pouch is formed along the ventral midline of the tail and is present below the anteriormost eight tail rings ( Fig. 11A ).

Distribution.— Acentronura breviperula is known from the tropical Indo-West Pacific, from East Africa, Madagascar, the Red Sea, Persian Gulf, Papua New Guinea, Torres Strait, northern Great Barrier Reef, Australia, New Caledonia, and Taiwan ( Fraser-Brunner and Whitley, 1949; Dawson, 1985; Kuiter, 2000, 2003; Fricke and Kulbicki, 2006; Chen, 2017; Fricke et al., 2019).

Material examined.— Acentronura breviperula: CAS 247135, female, 40.1 mm SL, channel between Iles aux Canards and Noumea , Anse Vate Bay, New Caledonia, 22°18 ' 23.8 '' S, 166°26 ' 07.9 '' E, depth 23 m, H. Hamilton and G. Short, 18 October 2008.

Figures

Fig. 8. Lateral view of preserved specimens of Acentronura spp. redescribed in this study. (A) A. breViperula, CAS 247135, female, 40.1 mm SL. (B) A. gracilissima, CAS-SU 6681, male, 70.4 mm SL. (C) A. tentaculata, CAS 247139, male, 50.8 mm SL. (D) A. tentaculata, CAS 247139, female, 53.9 mm SL.

Fig. 9. Lateral view of µCT scanned skeletons of preserved specimens of Acentronura spp. redescribed in this study. (A) A. breViperula, CAS 247135, female, 40.1 mm SL. (B) A. gracilissima, CAS-SU 6681, male, 70.4 mm SL. (C) A. tentaculata, CAS 247139, male, 50.8 mm SL. (D) A. tentaculata, CAS 247139, female, 53.9 mm SL.

Fig. 10. Dorsal view of µCT scanned neurocranium of (A) Acentronura breViperula, CAS 247135, female; (B) Acentronura gracilissima, CAS 247139, male; (C) Acentronura tentaculata, CAS-SU 6681, male. Abbreviations: BLP, bilateral lobed protuberances; SC, supraoccipital crest.

Fig. 11. X-ray radiography of (A) A. breViperula, BMNH 1890.1.14.51, male, holotype; (B) A. tentaculata, BMNH 1869.6.21.7, male, holotype; (C) I. larsonae, NTM S.10805-001, male, holotype, 55.5 mm SL (Photograph credits for A. breViperula and A. tentaculata to Oliver Crimmen and Ralf Britz, © The Trustees of the Natural History Museum, London; I. larsonae to Michael Hammer, © Museum and Art Gallery of the Northern Territory).