Argyrotheca Dall, 1900

Logan, Alan & Bitner, Maria Aleksandra, 2013, New records of Recent Brachiopoda from the Red Sea with a description of a new species, Zootaxa 3746 (1), pp. 161-174 : 168-171

Genus Argyrotheca Dall, 1900

Type species. Terebratula cuneata Risso, 1826 .

Argyrotheca somaliensis Cooper, 1973 Fig 5 A–H

1973 Argyrotheca somaliensis Cooper , p. 16–17, pl. 5, figs. 1–19.

Type locality. Northeast end of the Somali Republic, Indian Ocean, depth 59–61m (Cooper 1973).

Material. 13 specimens (9 ventral valves and 4 dorsal valves) from 2 localities in the Sudan (GZ 93/10 and GZ 100/8) and 2 localities in the Gulf of Aqaba, Egypt ( TAU 28 and TAU 39).

Description. Shell small (maximum observed length 5.7 mm), transversely subrectangular in outline, ventribiconvex. Shell endopunctate, surface covered with wide, rounded costae, up to 16; intercalate ribs present. Foramen large, hypothyrid, triangular, bordered by narrow deltidial plates. Ventral valve interior with long, narrow teeth lying parallel to the hinge margin and bearing diagonal ridges. Pedicle collar relatively narrow, supported by a slender median septum that extends to mid-valve; anterior to the septum are small, shallow depressions to accommodate serrations of dorsal septum.

Dorsal valve interior with short but thick inner socket ridges and prominent cardinal process ( Fig. 5 F). Hinge plates attached to septum, forming a deep, broad trough; crura short, crural processes partly broken, as there is a loop. Septum thick, high, triangular in profile, anterior slope of the septum with 4–5 serrations.

Remarks. The studied specimens correspond well to those described and illustrated as Argyrotheca somaliensis from off Somalia by Cooper (1973). They differ, however, in being larger and having more numerous ribs. Cooper (1973) also observed fewer serrations in his specimens. This is the first record of this species from the Red Sea.

Argyrotheca jacksoni Cooper, 1973 Fig. 6 A–M

1973 Argyrotheca jacksoni Cooper , p. 17, pl. 3, figs. 9–13.

2008 Argyrotheca jacksoni Cooper - Bitner et al., p. 282–284, fig. 3. 2008 Argyrotheca jacksoni Cooper - Logan et al., p. 303, figs. 3G–O.

Type locality. Ras Muhammad, southern tip of Sinai Peninsula, Red Sea, depth 10m (Cooper 1973).

Material. 42 specimens (28 bivalved specimens, 8 ventral valves and 6 dorsal valves), mostly from localities in the Sanganeb reef areas and Suakin Archipelago off the Sudanese coast, and in the Gulf of Aqaba, Egypt (see Table 1). All specimens are empty shells devoid of soft parts.

Remarks. This species is the commonest brachiopod in the Red Sea. It is characterized by its thin shell, small size (length of ventral valve rarely exceeding 2mm: see also comments on the holotype measurements in Bitner et al. 2008) and numerous, gently rounded ribs. The investigated specimens are consistent with the specimens of this species recorded by Logan et al. (2008) from the Red Sea. The specimens of A. jacksoni described from the Persian Gulf (Bitner et al. 2008) differ slightly from those studied here in having more marked ribs. In outline and ornamentation the specimens from the Red Sea are similar to A. cuneata (Risso) from the Mediterranean Sea, however, they lack a pink-red wash between the costae, characteristic for A. cuneata .

Argyrotheca cooperi Bitner & Logan sp. nov. Fig. 7 A–K

2008 Argyrotheca sp. A, Logan et al., p. 303, fig. 3P–T.

Diagnosis. Small Argyrotheca with a wide hinge line and 4–6 heavy rounded ribs, producing scalloped anterior margin.

Etymology. In commemoration of the late renowned brachiopod specialist, Dr. G. Arthur Cooper.

Type locality. Suakin Archipelago, Sudan, 18° 57’N, 38° 15’E, at 90m.

Holotype. The specimen (dorsal valve) illustrated in Fig. 7 I–K from GZ100/8 at a depth of 90m, NHMW 103349.

Paratypes. The specimens figured in Fig. 7 A–H, NHMW 87192/GP/243–246, NHMW 103346–103347.

Material. 4 ventral valves from Mersat Abu Samra, Gulf of Aqaba, Egypt, TAU 28, and 4 dorsal valves from Suakin Archipelago, Sudan, GZ 100/8.

Dimensions of holotype (in mm). Length 1.6 mm, width 2.8 mm.

Description. Shell thick, very small (maximum observed length 2 mm and width 2.8 mm), subrectangular to transversely elongate in outline, with a wide hinge margin. Shell coarsely endopunctate; shell surface covered with wide, heavy rounded ribs, 4 to 6 in number, forming scalloped anterior margin. Ventral valve convex, with large, triangular hypothyrid foramen bordered by 2 narrow deltidial plates in the form of ridges. Interarea flat, beak ridges sharp; pedicle collar relatively narrow, supported by a septum. Teeth long, parallel to hinge margin. Dorsal valve gently convex, with inner socket ridges narrow but thick. Cardinal process prominent; hinge plates attached to a septum forming septalium; median septum triangular in profile, high anteriorly. Crura and loop not preserved.

Remarks. The material described here consists of separate valves. By its ornamentation this species is easily distinguishable from other Argyrotheca species of the Red Sea. In ornamentation it resembles A. grandicostata Logan, 1983 from the Canary Islands but it differs in having a much longer hinge line (Logan 1983b). In their very broad hinge margin the studied specimens are close to A. angulata Zezina, 1987 from the Mozambique Channel but they can be easily distinguished from the latter species by their heavy ribbed ornamentation while A. angulata is sculptured by four feeble ridges (Zezina 1987).

Figures

FIGURE 5. Argyrotheca somaliensis Cooper, 1973, Red Sea. A. Outer view of ventral valve, GZ 100 / 8, 90 m, NHMW 87192 / GP / 229. B. Outer view of dorsal valve, GZ 93 / 10, NHMW 87192 / GP / 230. C. Inner view of ventral valve, GZ 100 / 8, NHMW 87192 / GP / 231. D – F. Dorsal valve, GZ 100 / 8, 56 m, NHMW 87192 / GP / 232. D. Inner view. E. Oblique view to show high median septum with four serrations. F. Enlargement of posterior part to show massive cardinal process. G – H. Dorsal valve, TAU 30, 136 – 145 m, off Nuweiba, Gulf of Aqaba, Egypt, NHMW 87192 / GP / 233. G. Inner view. H. Oblique view. Scale bars: A, 2 mm; B – E, G – H, 1 mm; F, 500 µm. All SEMs.

FIGURE 6. Argyrotheca jacksoni Cooper, 1973, Red Sea. A – B. Dorsal views of complete specimens, A. SM 4 A, NHMW 87192 / GP / 234, B. AB 24, NHMW 87192 / GP / 235. C. Ventral view of complete specimen, SM 4 A, NHMW 87192 / GP / 236. D – E. Dorsal views of complete specimens, D. SM 6 B, NHMW 87192 / GP / 237, E. SM 8 B, NHMW 87192 / GP / 238. F – H. Ventral valve, SM 9 A, NHMW 87192 / GP / 239. F. Inner view. G – H. Enlargement of posterior (G) to show details of the beak and of a tooth (H). I. Inner view of ventral valve, GZ 100 / 8, NHMW 87192 / GP / 240. J – M. Dorsal valves, SM 5 B, J. NHMW 87192 / GP / 241, K – M. NHMW 87192 / GP / 242. J. Inner view. K. Inner view. L – M. Oblique and tilted views to show high median septum, short crura and crural processes. Scale bars: A – F, I – M, 500 µm; G, 200 µm; H, 100 µm. All SEMs.

FIGURE 7. Argyrotheca cooperi Bitner & Logan sp. nov., Red Sea. A – C. Outer views of ventral valves, TAU 28, Gulf of Aqaba, off Mersat Abu Samra, NHMW 87192 / GP / 243 – 245. D – E. Ventral valve, TAU 28, Gulf of Aqaba, off Mersat Abu Samra, NHMW 87192 / GP / 246. D. Inner view. E. Enlargement of posterior part. F. Outer view of dorsal valve, GZ 100 / 8, 90 m, NHMW 103346. G – H. Dorsal valve, GZ 100 / 8, 90 m, NHMW 103347. G. Inner view. H. Enlargement of posterior to show details of cardinalia. I – K. Dorsal valve, GZ 100 / 8, 90 m, holotype, NHMW 103349. I – J. Inner and side views. K. Enlargement of posterior part to show cardinal process and cardinalia. Scale bars: A – G, 500 µm; H, K, 200 µm; I – J, 1 mm. All SEMs.