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 : 425-427

Minutella cf. minuta ( Indonesia)

In the ventral valve the presence of the pseudodeltidium is confirmed in the earliest developmental stages and thus is a generic character of Minutella as already pointed out by Hoffmann and Lüter (2010, p. 155–156). The shape and the structure of the ventral valve do not change significantly throughout growth. On the contrary, the shell development of the dorsal valve follows a precise, hierarchic and complex ontogenetic development.

PLATE 7. Ontogenetic stages of Ospreyella mutiara n. sp. Size of the specimens indicated with scale bars. Fig. 1. RBINS-RI-BRA 51, paratype. Specimen with posterior part of the median ramus bent backwards. Anteriorly a very narrow median depression appears. The major interbrachial lobes are widened and appear ovate. 1a: Ventral view. 1b: Detailed view.

Fig. 2. RBINS-RI-BRA 52, paratype. In this specimen the median depression is wider and more characteristic like in other representatives of the genus Ospreyella . 2a: Ventral view. 2b: Lateral view. 2c: Oblique anterior view. Fig. 3. RBINS-RI-BRA 33, paratype. Ventral view of the largest dorsal valve with male features. The major interbrachial lobes are elongated and the posterior portion of the median ramus is entirely pointing backwards. Two lateral ramuli are formed in correspondence with the emerging minor interbrachial lobes.

Fig. 4. RBINS-RI-BRA 53, paratype. This developmental stage is only observed in dorsal valves with female features. The marsupial notch is formed in the brachial bridge. The median ramus is a trifid structure dominated by the developing ramuli. The ventral concavity in the median ramus is filled with shell material. The major interbrachial lobes are semicircular. The asymmetrical minor interbrachial lobes are extending anterior. 4a: Ventral view. 4b: Lateral view. 4c: Oblique anterior view. 4d: Oblique posterior view with emerging marsupial notch.

Fig. 5. RBINS – RI – BRA 36, paratype. In this specimen the ramuli and the minor interbrachial lobes are extending anteriorly. The lophophore attachment muscle scars are characterised by regularly spaced small ridges. 5a: Ventral view. 5b: Lateral view. 5c: Oblique anterior view.

Fig. 6. RBINS – RI – BRA 54, paratype. In this almost fully grown specimen the ramuli are slender with their central concavity closing due to successive growth. The minor interbrachial lobes are extending far anteriorly but remain without furcation. The lophophore attachment muscle scars are well-defined. 6a: Ventral view. 6b: Oblique antero-lateral view. 6c: Oblique lateral view. 6d: Oblique anterior view.

PLATE 8. Ospreyella sp. (Europa Island). Size of the specimens indicated with scale bars.

Fig. 1. MNHN-BRA-2312. A complete adult specimen (sex unknown) attached in living position to a dead coral. The shell of is transversely ovate, much wider than long and the interarea is rather short. 1a: Dorsal view. 1b: Oblique anterolateral view.

Fig. 2. MNHN-BRA-2232. Ventral valve of an adult specimen with intact hemispondylium. (Photo A. Logan) Fig. 3. MNHN-BRA-2232. A ventral valve of a smaller specimen seen in oblique anterior view. The anterior part of the pseudodeltidium is perforated by cavities which do not represent punctae as in O. mutiara n. sp. (Photo A. Logan) Fig. 4. MNHN-BRA-2232. Dorsal valve of an adult specimen. The brachial bridge is broken. A long, slender minor interbrachial lobe, the jugum, the very wide and concave ramuli and the major interbrachial lobes are clearly visible. The uplifted median ramus with its narrow base is characteristic for representatives of the genus Ospreyella . In Lacazella the median ramus is entirely fused to the valve floor. 3a: Ventral view. 3b: Oblique anterior view. 3c: Oblique lateral view. 3d: Oblique posterior view.

Fig. 5. MNHN – BRA – 2232. Adult dorsal valve in ventral view with intact brachidium. The median ramus is relatively thin in this specimen but it exhibits secondary digitations. The ramuli are very wide and concave. Slightly asymetrical and relatively wide major interbrachial lobes are clearly visible. (Photo A. Logan).

Fig. 6. MNHN – BRA – 2232. Dorsal valve of another adult specimen with a still incomplete ontogenic development: the median ramus is still wide and concave, without secondary digitations. The marsupial notch is visible. (Photo A. Logan). Fig. 7. MNHN – BRA- 2232. A juvenile dorsal valve in ventral view. The median ramu and the ramuli are poorly developed. The major interbrachial lobes are clearly visible. (Photo A. Logan).

In the earliest developmental stage found in the investigated material (Pl. 2, Fig. 2a–c) the cardinal process is short and does not extend far beyond the posterior edge of the valve. The brachial bridge is complete and already relatively broad. The peribrachial ridge is well developed on the lateral side of the valve as a row of strong tubercles. However, in the anterior part of the valve the peribrachial ridge is only a smooth ridge (Pl. 2, Fig. 2b).

The calcitic pole is missing (Pl. 2, Fig. 2c). The valve floor is free of any shell structure, smooth, and with some large punctae.

In the next ontogenetic stage the two fused sub-parallel spikes in the middle of the valve floor (Pl. 2, Fig. 3a–c) form a U-shaped structure. The cardinal process becomes more prominent but the calcitic pole is still absent (Pl. 2, Fig. 3c). In the anterior part of the valve the peribrachial ridge is now represented by a row of strong tubercles. Lateral expansions are developing on either side of the fused median spikes (Pl. 2, Fig. 4). The median septum is still absent. A pointed triangular structure appears in the middle of the dorsal side of the brachial bridge. This is the precursor of the calcitic pole.

In the next available stage (Pl. 2, Fig. 5a–c) the two central, medially fused spikes are growing backwards forming a V-shaped structure. Simultaneously, the lateral extensions build the posterior part of the intrabrachial ridges. The median septum appears in the middle of the valve floor and extends anteriorly (Pl. 2, Fig. 5b). The slender, lamellar calcitic pole is now formed and first posterior outgrowths are present (Pl. 2, Fig. 5c). A slightly more advanced stage of growth is presented in Pl. 2, Fig. 6a–b.

Later, the median septum reaches the peribrachial ridge and brachial cavity tubercles form drawing the limit of the brachial lobes (Pl. 2, Fig. 7a–b). At the next stage, more brachial cavity tubercles are progressively added and the anterior part of the median septum is bifurcate and fused as a triangular structure to the peribrachial ridge (Pl. 2, Fig. 8a–c). The ontogenetic development is finalised (in female specimens) by the completion of the brachial lobes with a brachial cover (Pl. 2, Fig. 1a–h).