Neorhynchia strebeli (Dall, 1908)

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Lectotype (per Cooper 1972) is lodged with the National Museum of Natural History, Washington (USNM 110741).

Synonymy

Hemithyris strebeli Dall, 1908

Neorhynchia profunda Cooper, 1972

‘Neorhynchia’ abyssa Cooper, 1972 [as a misspelling of Notorygmia abyssa]

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Fig. 10. Neorhynchia strebeli and comparative material. A–C) Dorsal, lateral, and anterior aspects of a thicker specimen with sub-erect beak (E22183; L=14.6 mm). D–F) Dorsal, lateral, and anterior aspects of a smaller specimen with straighter beak (E22182; L=12.1). G, H) interior of dorsal valve (ventral aspect), depicting whole valve (G), and close-up of cardinalia (H) (E21963; L=12.7). I–K) Cardinalia close-up ventral aspect (I) and left and right semi-lateral aspects from another specimen highlighting cardinalia variation (E22183; L = 13.8 mm). L) Dorsal closeup of beak (same specimen as A–C). M, N) Dorsal aspect (M) and antero-dorsal aspect (N) of delthirium and beak interior, depicting hinge teeth and dental plates (lamellae) (same specimen as I–K). O, P) Abyssothyris wyvillei comparative material collected with N. strebeli, anterior (O) and dorsal (P) aspects (E22184; L=12.2 mm, T=6.5 mm). Abbreviations per Methods with ‘*’ marking site of broken-off ‘ISR’ (on I–K demarcated by dashed red outline). Scale bars: 10.0 mm (G), 5.0 mm (A–E, L, M, O, P, with F & N approximately same scale as E & M respectively), 2.0 mm (H, I, with J & K approximately same scale as I).

Table 6. Neorhynchia strebeli measurements, notes, and indices. All measurements in mm, NA = not assessable as valves were disarticulated, * = dry specimens (others in ethanol).

Diagnosis: Suboval, subtrigonal, to pentagonal; biconvex to slightly ventribiconvex, typically sulcate (but sometimes uniplicate or rectimarginate), smooth and impunctate; broad but deep, arcuate anterior commissure; beak short, hypothyridid; foramen moderate, deltidial plates disjunct. Crura short, gently arcuiform. Lophophore spirolophous. (Modified from Emig 2022). Genus is monotypic and so the diagnosis is for the genus also.

Etymology: Specific epithet in honour of German malacologist Dr. Hermann Wilhelm Strebel (1834−1914).

Description

Overall valve form: Maximum valve length 14.6 mm (average 13.4 mm, SD 0.96, smallest specimen 12.1 mm long). Valves rather wide with some specimens having width equal to valve length, W%L average 92.8% (SD 6.3, range 82.7%–100.7%). Valves with moderate thickness, T%L averaging 55.0% (SD 3.9, range 50.0%−61.6%).

Overall valve shape rounded subtriangular, widest point slightly anterior to mid-valve. Valves equally biconvex, or with the dorsal (brachial) valve slightly deeper. Lateral commissure flat or slightly curved towards the ventral (pedicle) valve. Anterior commissure variably sulcate, anterior edge folded slightly or moderately towards the ventral valve (Fig. 10 A–F). Dorsal valve with median groove very shallow. Valves impunctate, translucent, and largely colourless. Relatively smooth but with fine growth striae.

Dorsal (brachial) valve: Cardinal margin approximately 110−112°. Cardinalia illustrated in Fig. 10 G–K. Cardinal process largely absent, a thin transverse ridge marking its place, with a small depression at the posterior end of the cardinalia possibly serving as the diductor muscle attachment (?). Sockets with outer and inner socket ridges well developed (inner ridge antero-laterally rounded or angular), the sockets slightly corrugated. Outer hinge plates broad and concave, bordered medially by cural bases. Inner hinge plates absent. Crura short and arcuiform (flattened; broader and truncated distally in lateral profile), diverging strongly at approximately 60°. Median septum a faint and low ridge, approximately restricted to the posterior 20%−30% of the dorsal valve length.

Ventral (pedicle) valve: Beak small, proportionally larger on smaller specimens and vice versa (length posterior to dorsal valve ~9%−12% of total valve length), variably straight to suberect. Foramen hypothyridid, collar short; deltidial plates small and disjunct, triangular, mostly exposed (see Fig. 10 L, M). Hinge teeth prominent and large relative to delthirium, supported by thin dental plates (see Fig. 10 N).

Soft tissue: Not in good condition on the few specimens examined, pedicle short (not extending beyond the beak posteriorly) and lophophore spirolophe (consistent with Zezina 2015) though poorly preserved).

Attachment substrata and epibiota: Specimens examined were lacking attachment substrates and epibiota.

Specimens examined

3 specimens, SE of Pt Hicks, NE Bass Strait, 38.4784°S, 149.5566°E, 1426−1509 m, SS200001 Stn 158, 17.iv.2000, TMAG E22183; 1 specimen, seamounts south of Tasmania, 44.2969°S, 147.1149°E, 1712−1465 m, IN2018_V06 Stn 11, 24.xi.2018, TMAG E22182; 3 specimens, seamounts south of Tasmania, 44.2394°S, 147.2929°E, 1354-1414 m, IN2018_V06 Stn 169, 14.xii.2018, TMAG E58672; 2 specimens, seamounts south of Tasmania, 44.2143°S, 146.2669°E, 1157-1353 m, IN2018_V06 Stn 74, 3.xii.2018, TMAG E21963.

Comparative material. Abyssothyris wyvillei, 1 specimen [L=12.2 mm, W=11.2 mm, T=6.5 mm], NE Bass Strait, 38.4784°S, 149.5566°E, 1426−1509 m, SS200001 Stn 158, 17.iv.2000, TMAG E22184.

Table 6. Neorhynchia strebeli measurements, notes, and indices. All measurements in mm, NA = not assessable as valves were disarticulated, * = dry specimens (others in ethanol).

Remarks

The sulcate anterior commissure, hypothyridid foramen, crura and septum form, and impunctate valves, all supported the assigning of material examined herein to Neorhynchia. This material was collected from the continental slope north-east of the Bass Strait, and from seamounts off southern Tasmania (Fig. 1 A), 1157−1712 m depth, apparently representing the first record of this genus from Australian waters. Interestingly, several specimens were captured with Dallina tasmaniaensis, sp. nov. (E22160 & E58675), and a putative Abyssothyris wyvillei (Davidson, 1878) (TMAG E22184, see comparative material; Fig. 10 O, P), indicating sympatric distribution with these species.

Other Rhynchonellid order brachiopods previously recorded from southern Australia are Aulites brazieri (Crane, 1886), Cryptopora gnomon Jeffreys, 1869, and Basiliolella colurnus (Hedley, 1905). Aulites and Cryptopora occur in Australia over similar depth to Neorhynchia (31–1143 and 974–1125 m respectively; Richardson 1997) but can be distinguished by their high median septum (septal pillar) roughly midway along dorsal valve, as well as differences in the crura. B. colurnus has a uniplicate anterior commissure (ventral valve anterior folding into the dorsal valve—opposite to Neorhynchia) and lives far shallower. TMAG has 19 lots of B. colurnus, all recorded over a bathymetric range of 158−280 m (slightly expanding the 188–203 m bathymetry range recorded by Zezina 2010). The Rhynchonellid genera Grammetaria Cooper, 1959 and Basiliola Dall, 1908 have been recoded adjacent to Australia (New Caledonia, per Laurin 1997), but should be readily distinguishable if they are ever recorded from Australia. The Terebratulid order Phaneropora galatheae Zezina, 1981 is externally alike Neorhynchia and occurs locally from 399–1463 m depth, but again has a septal pillar and is punctate (unlike the Rhynchonellids), and is substantially smaller than Neorhynchia (Richardson 1997). Finally, Cooper (1927) notes N. strebeli as very similar in external form to the Terebratulid brachiopod Abyssothyris wyvillei (Davidson, 1878), however, while these species co-occurred herein A. wyvillei was also clearly distinguishable by the presence of puncta, as well as conjunct deltidial plates, and absence of median septum.

N. strebeli is broadly distributed throughout the Pacific Ocean from 2560–4513 m depth (Zezina 2010). Records from the western Pacific are limited, Cooper (1927) noted a 15 mm long N. strebeli from Challenger Station 184, south of New Guinea (2560 m), while Laurin (1997) described a 12.3 mm long specimen captured at L'Île-des-Pins (2660 m depth), eastern Coral Sea, and referred to another captured further south in the New Caledonia basin (2930 m). Barnes & Peck (1997) recorded further specimens from the Weddell Sea, Antarctica (814 m), with maximum length 22.1 mm, with Foster (1989) recording it from the far southern Pacific (42−63°S, 74−128°W).

The size range (no more than 14.6 mm) of this Australian N. strebeli material was comparable to that described by Cooper (1927) and Laurin (1997) from the western Pacific. The bathymetric range (1426–1712 m) was within the range expected (when considering Barnes & Peck 1997 and Zezina 2010). Considering how widespread this species is in the Pacific Ocean, it is unsurprising that it would eventually be collected from Australia. Cooper (1972) recognized two species of Neorhynchia, describing material from the north-eastern Pacific as N. profunda Cooper, 1972, diagnosed by having a consistently greater length than width (the Type material of N. strebeli having greater width than length). Later authors have not recognized this species, likely as N. strebeli is far more variable than initially realized, but in any case, N. profunda W%L indices (79.6%−97.9%; fide Cooper 1972) fit the W%L indices of the Australian material. Databases (e.g., WoRMS 2022b) also list a Neorhynchia abyssa Cooper, 1972, however while Cooper (1972) described the Terebratulid Notorygmia abyssa Cooper, 1972 (since synonymized under Macandrevia diamantina Dall, 1895), he did not describe a Neorhynchia with this name. Instead, Cooper (1927; p.5) contained a single usage of ‘Neorhynchia abyssa’ when listing locality data, apparently little more than a typographic mistake for Notorygmia abyssa which was mistakenly copied into databases.