Thecidellina Thomson 1915

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 : 166-168

Genus Thecidellina Thomson 1915

Type species. Thecidium barretti Davidson, 1864 .

Thecidellina blochmanni Dall, 1920 ( Fig. 4 A–L)

1920 Thecidellina blochmanni Dall , p. 283.

1970 Thecidellina australis blochmanni Dall - Pajaud, p. 245, pl. II, fig. 10 and text-fig. 110. 1973 Thecidellina blochmanni Dall - Cooper, p. 8, pl. 8, figs 27–30. 2003 Thecidellina blochmanni Dall - Lee and Robinson, p. 354.

2008 Thecidellina sp. indet. - Logan et al., p. 302, fig. 2H.

Type locality. Flying Fish Cove, Christmas Island, eastern Indian Ocean, depth 84m (Dall, 1920), original specimens collected by C.W. Andrews, 1909 (see Lüter and Sieben 2005).

Material. 26 specimens (24 dorsal valves), mostly from localities in the Sanganeb reefs area of the Sudanese coast off Port Sudan and Suakin (see Fig. 1 and Table 1). None have soft parts and most show evidence of transportation, likely parautochthonous (Logan et al. 2008).

Description. Shell small for genus, length of ventral valve rarely exceeding 4mm, width about 3.5mm, shell usually longer than wide, endopunctate, anterior commissure rectimarginate, fibrous secondary shell restricted to cardinal process, teeth and tubercles. Ventral valve cemented to substrate by small protegulum. Interarea flat (planodeltidium of Logan and Baker 2013), finely striated with parallel growth lines, hinge teeth prominent, triangular, hemispondylium fused to valve floor, no supporting septum, prongs apically pointed, medially fused, but not usually intact. Dorsal valve smaller than ventral valve, usually elongate; cardinal process bilobate, additional median lobe only weakly developed; dental sockets on either side of cardinal process; calcitic pole attached to bridge and cardinal process, massive with flat sides in adults; median septum variable in width, arched in juveniles, diverging anteriorly, flat or slightly crested posteriorly, changing to concave anteriorly; brachial cavities deep, floored by occasional tubercles, usually found uncovered but sometimes with delicate canopy where preserved, rows of heavy ridges radiating towards the centre or bouffant-like aggregations of shell; peripheral rim with tubercles.

Remarks. Lüter and Sieben (2005, p. 188) have outlined the history of this species, culminating in the subsequent loss from the National Museum of Natural History in Washington of the sole specimen, the holotype, described by Dall. Fortunately, 12 of the original topotypes collected by Andrews in 1909 are in the Natural History Museum in London and 6 in the Humboldt University Museum in Berlin and in addition there is topotypic material in Berlin collected from Flying Fish Cove by a Western Australian Museum expedition to Christmas Island. One of these is figured here ( Fig. 4 F). Details of the characteristic patterns of shell aggregations in the brachial cavities of the dorsal valve are shown in Figs. 4 C, F and I.

The Red Sea specimens are smaller than those from Christmas Island and the median lobe of the cardinal process is less well-developed but in other features it corresponds closely to the eastern Indian Ocean species. The species is slightly more common than Minutella minuta in the collections from the Red Sea and has been found at more localities, mostly in the Sudan ( Table 1). A single juvenile ( Fig. 4 J–L) from Dahab, Gulf of Aqaba, Egypt was collected by Zuschin beneath a colony of the coral Acropora at 10m depth.

Superfamily Megathyridoidea Dall, 1870 Family Megathyrididae Dall, 1870

Figures

FIGURE 1. Map of the Red Sea showing location of collecting localities listed in Table 1.