Idiotropiscis australe ( Waite and Hale, 1921 )

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 : 824-827

Idiotropiscis australe ( Waite and Hale, 1921)

Figures 12 , 13 ; Tables 2–5

Acentronura australe Waite and Hale, 1921: 317–318 , fig. 53 ( St. Vincent Gulf, South Australia).

Diagnosis.— See generic diagnosis. Idiotropiscis australe differs from its congeners by the following combination of characters: distinct raised bony multipartite dorsomedial crest on the supraoccipital, the four segments arcuate in lateral view, spanning the complete frontal from anterior margins of the interorbital to the supraoccipital, protruding anteriorly; posterolateral margins of post-temporal bones expanded moderately anteriorly taking the form of curved protuberances; small dorsal snout spine present medially on mesethmoid bone.

Description.— General body shape as in Figure 13 . 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, rising from short snout to an elevated supraoccipital; distinct raised bony multipartite dorsomedial crest on the supraoccipital, the four segments arcuate in lateral view, spanning the complete frontal from anterior margins of the interorbital to the supraoccipital, protruding anteriorly; posterolateral margins of post-temporal bones expanded moderately anteriorly taking the form of curved protuberances ( Fig. 14A ); anterior nuchal plate absent ( Fig. 13A ); posterior nuchal plate present anterior to cleithrum with dorsomedial crest-like ridge along its dorsum, large gap present 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 openings as small bilateral slits directly situated laterally on head between supraoccipital and cleithrum; small dorsal snout spine present medially on mesethmoid bone; interorbital narrow, depressed; opercular ridge low, entire, angled dorsally toward gill opening; slight swelling of gular region ventroposterior to eye; pectoral-fin base without distinct ridges, on strongly elevated ventrolateral bulge; trunk deepest anteriorly, principal body ridges distinct; principal body ridge spines absent. Caudal fin absent. Idiotropiscis australe exhibits strong sexual dimorphism associated with the presence of a male brood pouch. The brood pouch is formed along the ventral midline of the tail and is present below the anteriormost 11 tail rings ( Fig. 12A ). µCT scanning of the material ( Fig. 13A ) revealed the brood pouch is enclosed by 11 arcuate bony extensions, which extend ventrolaterally from the anterior ventral plate ridges of the tail and are reduced in size posteriorly. The anteriormost pouch plate is broad and paddle-shaped at ventrocaudal margin and curved posterolaterally relative to other pouch plates. The posteriormost pouch plate is diminutive in size.

Distribution.— Idiotropiscis australe is endemic to the temperate waters of southern and southwestern Australia, from Cape Jarvis and the Gulf St Vincent, South Australia, and Carnac Island, Western Australia ( Dawson, 1985).

Material examined.— Idiotropiscis australe: SAMA F2657 , Yankalilla, South Australia, Australia, 35.597767°S, 138.097511°E, depth 20 m; WAM P.25346-015 , Australia, Western Australia, Carnac Island, Gage Roads , dredge, J. Scott, 30 June 1975; WAM P.33542-001 , Success Bank , Cockburn Sound, Western Australia, 32.083097°S, 115.683344°E, depth 4 m, 3 November 1997; WAM P.33543-001 , male, Owen Anchorage , Cockburn Sound, Western Australia, Australia, 32.114459°S, 115.749989°E, depth 12 m, 1 November 1997.

Figures

Fig. 12. Lateral view of preserved specimens of Idiotropiscis spp. redescribed in this study. (A) I. australe, WAM P.33543-001, male, 54.7 mm SL. (B) I. larsonae, NTM S.10805-001, male, holotype, 33.5 SL. (C) I. larsonae, GCRL 21518, female, paratype, 33.0 mm SL. (D) I. lumnitzeri, CAS HH-0423, male, 69.9 mm SL. (E) I. lumnitzeri, AMS I.45395-001, female, 54.0 mm SL.

Fig. 13. Lateral view of µCT scanned skeletons of preserved specimens of Idiotropiscis spp. redescribed in this study. (A) I. australe, WAM P.33543- 001, male, 54.7 mm SL. (B) I. larsonae, GCRL 21518, female, paratype, 33.0 mm SL. (C) I. lumnitzeri, CAS HH-0423, male, 69.9 mm SL. (D) I. lumnitzeri, AMS I.45395-001, female, 54.0 mm SL.

Fig. 14. Dorsal view of µCT scanned neurocranium of the head of (A) Idiotropiscis australe, WAM P.33543-001, male; (B) Idiotropiscis larsonae, GCRL 21518, male; (C) Idiotropiscis lumnitzeri, CAS HH-0423, male. Abbreviations: BLP, bilateral lobed protuberances; SC, supraoccipital crest.