Ospreyella mutiara, Simon, Eric & Hoffmann, Jana, 2013

Simon, Eric & Hoffmann, Jana, 2013, Discovery of Recent thecideide brachiopods (Order: Thecideida, Family: Thecideidae) in Sulawesi, Indonesian Archipelago, with implications for reproduction and shell size in the genus Ospreyella, Zootaxa 3694 (5), pp. 401-433 : 427-428

Ospreyella mutiara n. sp.

In the earliest juvenile stage of growth found in the material collected from Donggala, the fundamental shell structures in the ventral valve are already developed, such as the teeth, the hinge line, the interarea and a welldefined pseudodeltidium. In the dorsal valve (Pl. 6, Fig. 1a–d) the sockets and the cardinal process are already present. The cardinal process is bilobed. Lateral adductors muscles scars are already visible (Pl. 6, Fig.1d). The brachial bridge is not complete and is formed by inwardly directed lateral growth of pointed structures which seem to be similar to the crura as described and illustrated by Logan (2008, p. 411, Figs 6.1–2). The dorsal valve floor is smooth without any spikes or spiculate construction. There is no subperipheral rim developed at this stage of growth.

Later, the crura-like shell elements form the brachial bridge by fusion (Pl. 6, Fig. 2a–d). However, at this stage the brachial bridge construction is not yet achieved (Pl. 6, Fig. 2d). A V-shaped structure consisting of two divergent spikes appears in the middle of the valve floor. The two spikes are separated from each other at their base. The lateral parts of the peripheral rim start to develop as strong tubercles. The postero-lateral subperipheral rim is well-developed and consists of two straight rims supporting the base of the cardinal process (broken in Pl. 6, Fig. 2) and the dental sockets.

In the following stage of growth, the cardinal process is trilobed (Pl. 6, Fig. 3b). The two median spikes are now fused at their base (as in Logan 2008, Fig. 6.2). The peripheral rim is completed anteriorly by several strong coalescent tubercles and a peripheral flange is perceptible. The brachial bridge is fully developed (Pl. 6, Fig. 3d).

In a later stage the divergent processes of the major interbrachial lobes which were initially growing posteriorly are bending laterally and then turn down anteriorly forming the first stages of the “apparatus descendens” (Backhaus 1959) (Pl. 6, Fig. 4a–b, 4g, 4h). This results in an M-shaped structure with its extremities slightly widened giving them a spoon-like shape. A median elongated shell structure, consisting of two faint ridges, is emerging at the anterior tip of the base of the joined spikes (Pl. 6, Fig. 4d–e).

In the following ontogenetic stage, the median ramus precursor appears as a pointed knob emerging from the anterior part of the median ridges (Pl. 6, Fig. 5a–g). This knob is the tip of a triangle emerging anteriorly (Pl. 6; Fig. 5e, 5f). These new structures are raised from the dorsal valve floor. The spoon-like structures, the precursors of the major interbrachial lobes, are widening and pointed outgrowths develop from their inner margins forming the inner margins of the major interbrachial lobes (“p” in Pl. 6, Fig. 5b).

In a further developed stage the tubercles defining the peripheral rim are more or less fused and form an elevated tuberculated rim (Pl. 6, Fig. 6a). Pointed processes arise from the central part of the intrabrachial ridges and almost reach the pointed processes secreted from the spoon-like structures of the major interbrachial lobe precursors. They are nearly fused at this stage of growth, forming subcircular holes underneath the intrabrachial ridges (Pl. 6, Fig. 6d). In this stage the growth of the median ramus progresses and the wide triangle, elevated from the valve floor, is fused with the the intrabrachial ridges forming the jugum (Pl. 6, Fig. 6f).

In the next ontogenetic stage, the jugum is fully developed (Pl. 6, Fig. 7a–c). The lateral holes under the intrabrachial ridges are progressively reduced in size during growth. In another specimen (Pl. 6, Fig. 8) the reduced size of the holes in the intrabrachial ridges is perceptible. However, they will never be totally filled by shell material and small holes remain present even in the most adult stages observed (Pl. 7, Figs 5a, 6a). The major interbrachial lobes continue to extend anteriorly. The median ramus is widened and its apex is curving backwards. Numerous, large endopunctae are visible along the peripheral rim.

In a more advanced stage the median ramus is curved backwards and a narrow median depression is appearing anteriorly (Pl. 7, Fig. 1a–b). In another specimen (Pl. 7, Fig. 2a–c), the median depression is wider. Two lateral small, pointed outgrowths appearing at the tip of the median ramus are the ramuli precursors (Pl. 7, Fig. 1b). The two major ovate interbrachial lobes are extending anteriorly.

In the next stage in shell development (Pl. 5, Fig. 5a–e; Pl. 7, Fig. 3) the major interbrachial lobes become more elongated. The median ramus is completely pointing backwards and the two lateral ramuli are welldeveloped. They are concave in their central part and their external sides are ornamented with regularly spaced spines. Simultaneously, the minor interbrachial lobes are appearing. The lophophore attachment muscle scars are incipiently visible as inconspicuous small spaced vertical ridges.

The next ontogenetic stage (Pl. 7, Fig. 4a–d) is characterised by the development of the marsupial notch. The median ramus is a long trilobed structure formed by the developing ramuli. The major interbrachial lobes are now nearly semicircular. The minor interbrachial lobes are extending anteriorly and often show an asymmetrical development (rarely the length of the two minor interbrachial lobes is equal). The ventral depression of the median ramus is filled with shell material, which can also be observed for the ventral depression of the ramuli in later stages.

In the latest stages of shell development all these characters are still reinforced (Pl. 7, Fig. 5a–c). The ramuli and the minor interbrachial lobes are much longer. The lophophore attachment muscle scars made of regularly spaced small ridges are now well-developed.

In a nearly adult stage (Pl. 7, Fig. 6a–d) the ramuli are relatively long with their central depression being filled secondarily with shell secretions. The minor interbrachial lobes remain without furcation throughout their entire development.