Fallax neocaledonensis Laurin, 1997

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Holotype lodged (by Laurin, 1997) with the Muséum National d'Histoire Naturelle, Paris (MNHN-IB-2009-196).

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Fig. 9. Fallax neocaledonensis. A−C) external aspects of disarticulated specimen (C153071, L = 17.6 mm), dorsal valve exterior (A), ventral valve exterior (B), and semi-lateral dorsal aspect of the specimen with the valves reconnected (C). D, E) ventral and dorsal aspects of specimen with pedicle attachment (C153071, L = 17.1 mm). F) lateral aspect of specimen with attachment (C153071, L = 18.6 mm). G–I) detail of larger specimen with damaged brachial loop (C153078, L = 21.2 mm), dorsal aspect of whole specimen (G), dorsal valve interior (H), and detail of cardinalia of same (I). J–M) dorsal valve interior depicting good condition cardinalia–brachidium complex (C153071, L = 17.6 mm), dorsal closeup of cardinalia and brachidium (J), right–left semi-lateral aspects of same (K, L), and brachidium relative to whole dorsal valve interior (M). N–P) dorsal valve interior and delthirium detail, whole valve interior (N), and closeup of delthirium (two specimens), angled to expose teeth supports (O, P) (N & P from C153071, L = 17.6 mm; O from C153078, L = 21.2 mm). Abbreviations per Methods. Scale bars: 5.0 mm. Photography A.C. Miller, Copyright: Australian Museum (used with permission).

Table 5. Fallax neocaledonensis measurements, notes, and indices. All measurements in mm (but more approximate as limited measurements were provided and others calculated from these). NA = not assessable as valves were disarticulated or suitable measurements/photos were not provided.

Diagnosis: Per description.

Description

Full measurements were not obtained from this material (photographs and limited measurements provided), and only a simplified description is given.

Overall valve form: Valve length 15.1–21.2 mm (average 17.6 mm). Valves broad, W%L averaging 97% (range 92.6%−103.5%), and relatively thick (T%L 57.6%−61.5%). Overall shape triangular (near equilateral) and thus broadest anteriorly. Valves biconvex, ventral valve slightly deeper. Lateral commissure curved towards dorsal (brachial) valve. Anterior commissure weakly intraplicate (plicosulcate), similar to Dallina tasmaniaensis, sp. nov., the folding creates two shallow indentations along the anterior margin. Valves punctate, slightly translucent, white. Relatively smooth with fine growth striae (radial markings absent). Overall form illustrated in Fig. 9 A–G, and Supplementary Fig. 1 E–H.

Dorsal (brachial) valve: Interior detail depicted in Fig. 9 H–M. Cardinal process largely absent (small V-shaped indent anterior to the umbo being the diductor attachment point). Hinge sockets well developed, inner socket ridges strongly diverging and steeply inclined (outer corners triangular). Outer hinge plates slightly grooved, demarcated from inner hinge plates by crura (crura laterally continuous with the outer hinge plates, and without a well-defined base). Inner hinge plates proportionally smaller, fused medially as excavate septalium, supported by median septum. Septalium shortest medially and thus indented at anterior border almost to level of the sockets. Crura short and broad in lateral profile, subparallel (or slightly diverging). Crural processes short and pointed, directed ventrally and slightly medially. Brachidium diploform, descending branches ribbon like, broadly fused posteriorly with crural processes and with short lateral connecting bands to the median septum. Ascending and transverse bands forming hood/funnel, loop being relatively small (compared to C. furcifera) with its anterior-most extent just short of 50% dorsal valve length. Median septum thin, dropping in height anterior to septalium before rising to junction with lateral connecting bands, before rapidly dropping off anterior to this and fusing with valve floor at just over 50% the dorsal valve length.

Ventral (pedicle) valve: Beak relatively small, suberect. Foramen subapical, small (diameter approximately 7%−8% overall valve length). Possibly mesothyridid, but beak ridges poorly defined, rounded. Pedicle collar reduced to a ring within foramen. Deltidial plates mostly exposed, fused as symphytium (seam present where the plates fused medially) (Fig. 9 N, P). Hinge teeth well-developed, relatively small, bases not thickened. Dental plates present, lamellar, straight, connecting to floor of valve (Fig. 9 O, P).

Soft tissue: Pedicle thin, short to relatively elongate (extending beyond foramen, greater than beak length). Lophophore not preserved on material examined.

Attachment substrata and epibiota: Three specimens were attached to small rocks (size < half valve length). Valves free of epibiota.

Specimens examined

5 specimens, SE of Brisbane, Queensland, 27.933°S, 154.050°E, 967 m, FRV Kapala, 6.xi.1978, AM C.153071; 2 specimens, off Smoky Cape, NSW, 31.300°S, 153.350°E, 1334 m, 22.ix.1969, AM C.153078.

Remarks

Australian Museum specimen lots (C.153071 and C.153078), were collected from southern Queensland and northern NSW coasts (967–1334 m) and identified by the late brachiopod expert Joyce Richardson as Fallax sp. in 1987. Initially it was suspected that these specimens would be further Dallina material, but they were found to not only have a campagiform loop, but lacked a cardinal process seen in C. furcifera and most importantly had distinctive dental lamellae. The overall form of the valves and the internal structures closely matched those described by Laurin (1997) for Fallax neocaledonensis, collected around New Caledonia, but without detailed comparison to Type material, this identification must be treated as tentative. This is the first confirmation of Fallax and family Aulacothyropsidae from Australian waters. However, the larger specimen in AM lot C153078 (L = 25.4), is excluded from the above description as it differs from the other specimens and may be comparable to Dallina. Its narrower form (W%L = 87%), considerably larger and more circular foramen (diameter 11.5% overall length), and light beige-brown colouration (rather than white) are all consistent with D. tasmaniaensis, sp. nov. (Supplementary Fig. 1 I–K).

F. neocaledonensis is distributed widely around New Caledonia, Fiji, and Tonga (Bitner 2009, 2015, 2019), and if conspecific these Australian specimens would represent a considerable range extension for the species. Zezina (2010) recorded a tentative Fallax sp. from the Arafura Sea (off northern Australia, 7°34′S, 132°44′E, 390 m depth). Zezina (1981) originally recorded this same specimen as ‘Campages (?) sp.’ but given its lack of cardinal process she was hesitant in this placement, and while its loop was presumably diploform (“the loop joins the septum near the middle of its length”) no comment was made on the dental plates.

The triangular form and diploform brachidium of this species may represent a point of confusion with C. furcifera and D. tasmaniaensis, sp. nov., however these putative F. neocaledonensis were collected from considerably greater depth than C. furcifera (< 439 m vs. 967–1334 m). It can be distinguished from both of these species by the presence of dental plates, a septalium shortest medially and indented at its anterior border (rather than longest medially forming a V-shape), and from Dallina is clearly distinguished by its diploform rather than teloform loop.

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