Ebiscothyris bellonensis, Bitner & Cohen, 2015, Bitner & Cohen, 2015

Bitner, Maria Aleksandra & Cohen, Bernard L., 2015, Congruence and conflict: case studies of morphotaxonomy versus rDNA gene tree phylogeny among articulate brachiopods (Brachiopoda: Rhynchonelliformea), with description of a new genus, Zoological Journal of the Linnean Society 173 (2), pp. 486-504 : 494-495

EBISCOTHYRIS BELLONENSIS GEN. ET SP. NOV.

( FIGS 7A–I , 8A–F , 9A–D )

Diagnosis

As for the genus.

Etymology

Referring to the Bellona Plateau, where part of the material was collected.

Holotype

The specimen illustrated in Figure 7E–H , IB-2013-1, was collected at station CP 2616 on the Chesterfield Plateau.

Paratypes

The specimens illustrated in Figures 7A–D, I and 8A– F , IB-2013-2 to IB-2013-6, were collected at stations CP 2557 and CP 2616.

Type locality

Cruise EBISCO, station CP 2616, Coral Sea, Chesterfield Plateau, 19°35.08′S, 158°49.83′E, 786–836 m depth.

Material examined

Coral Sea , cruise EBISCO, western Bellona Plateau: station DW 2544, 21°09.91′S, 158°38.15′E, 650– 723 m depth, five specimens ; station CP 2545, 21°10.04′S, 158°37.40′E, 765–778 m depth, three specimens; station CP 2556, 21°05.29′S, 158°33.72′E, 741– 791 m depth, nine specimens; station CP 2557, 21°06.05′S, 158°31.66′E, 800–923 m depth, three specimens. Chesterfield Plateau : station CP 2616, 19°35.08′S, 158°49.83′E, 786–836 m depth, 28 specimens .

Depth range

650–923 m.

Measurements (station, length, width, and thickness, all in mm)

CP 2616 (holotype), 13.1, 12.0, 8.1; CP 2616 (paratype), 13.1, 12.3, 7.1. Measurements of all currently available specimens of E. bellonensis gen. et sp. nov. are given in Appendix S7.

Description

Shell of medium size, white, thin to translucent anteriorly, elongate oval to subpentagonal in outline, with maximum width at about mid valve. Shell surface smooth, with weakly defined growth lines; lateral and anterior valve margins slightly incurved, thickened ( Fig. 7C, D, G, H ). Shell biconvex, ventral valve more convex. Lateral commissures dorsally curved, anteri- or commissure strongly and broadly unisulcate. Beak short, suberect to erect. Foramen of medium size, circular, permesothyrid. Deltidial plates conjunct, forming a well-exposed symphytium with only a weak median line of junction in some specimens (cf. Fig. 8A ). Pedicle variable, may be as much as ten times as long as the shell ( Fig. 7I ). The long pedicle differentiates E. bellonensis gen. et sp. nov. from Abyssothyris and other terebratulids. Ventral valve interior with welldeveloped tubular, excavate pedicle collar ( Fig. 8F ). Teeth small, short ( Fig. 8A ). Dorsal valve interior with long and medially inclined inner socket ridges that bound wide sockets; fulcral plates well developed. Cardinal process prominent, semi-elliptical ( Fig. 8D, F ). Outer hinge plates narrow, triangular; crural bases ill defined. Loop short, occupying about 25% of dorsal valve length, with blunt, short, crural processes directed ventrally ( Fig. 8B–E ). Descending branches subparallel, very wide; transverse band broad, medially folded. Muscle scars strongly impressed on both valves, elongate oval in outline.

Ultrastructural analysis shows three shell layers ( Fig. 9A–D ). The microgranular primary layer is 5.2– 7.8 μm thick, the secondary layer is very thin (3.2– 5.6 μm), and its fibres are wide, implying that mantle epithelial cells are large, and/or that the angle between the fibres and the primary layer is small. In transverse section, the secondary layer shows only two overlapping layers of fibres ( Fig. 9B ), a feature that has only been reported before in the dyscoliid Xenobrochus norfolkensis Bitner, 2011 ( Bitner, 2011: fig. 4E, F); however, the incurved, thickened valve margins are built of several, densely arranged sheets of secondary fibres (see Fig. 9C ). The tertiary layer of E. bellonensis gen. et sp. nov. is thick (85–152 μm), with its internal surface showing clear traces of large, irregularly interlocking prisms ( Fig. 9C, D ). The total shell thickness is 96–160 μm. In Kanakythyris ( Fig. 9E, F ) the shell is also composed of three layers; however, the secondary layer is much thicker, and the prisms are more irregular on the internal surface, and display delicate ornamentation ( Fig. 9F ), whereas in E. bellonensis gen. et sp. nov. they are smooth (see Fig. 9D ).

Figures

Figure 7. Ebiscothyris bellonensis gen. et sp. nov., cruise EBISCO, Coral Sea, South-West Pacific: A–H, ventral, dorsal, lateral, and anterior views of complete specimens, CP 2616, 786–836 m depth; A–D, paratype, IB-2013-2; E–H, holotype, IB-2013-1. I, dorsal view of complete specimen, with very long, thin pedicle, paratype, CP 2616, 786–836 m depth, IB- 2013-3. Scale bars: 5 mm.

Figure 8. Ebiscothyris bellonensis gen. et sp. nov., cruise EBISCO, Coral Sea, South-West Pacific, SEM micrographs: A, inner view of ventral valve to show symphytium with a weak line of junction, and small teeth, paratype, CP 2616, 786–836 m depth, IB-2013-4; B–E, inner, tilted, posterior, and side views of dorsal valve to show brachidium and cardinalia, paratype, CP 2557, 800–923 m depth, IB-2013-5; F, inner view of posterior part of complete specimen to show tubular pedicle collar and cardinal process, paratype, CP 2616, 786–836 m depth, IB-2013-6. Scale bars: 1 mm.

Figure 9. Ebiscothyris bellonensis gen. et sp. nov., cruise EBISCO, Coral Sea, South-West Pacific, SEM micrographs; A, B, ventral valve, station CP 2556, 741–791 m depth, IB-2013-7; A, transverse section of the entire shell showing the primary layer (pri) underlain by the fibrous secondary layer (sec), passing into the prismatic tertiary layer (ter); B, section of the shell showing primary (pri), secondary (sec), and tertiary (ter) layers; a puncta with a radiating brush is also visible; C, D, dorsal valve, CP 2557, 800–923 m depth, IB-2013-5; C, latero-oblique view of internal surface, showing the incurved valve margin built of densely arranged sheets of secondary fibres (left) and prisms of tertiary layer (right); D, internal surface showing discrete units of prisms and very small punctae (arrows). E, F, Kanakythyris pachyrhynchos Laurin, 1997, cruise NORFOLK 2, Norfolk Ridge, station DW 2136, 402–410 m depth; E, transverse section of the entire shell; F, internal surface with discrete units of prisms. Scale bars: A, C, D, E, F, 50 μm, B, 20 μm.