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 : 412-422

Ospreyella mutiara n. sp.

Pl. 3, Figs 1–8; Pl. 4, Figs 1–10; Pl. 5, Figs 1–6; Pl. 6, Figs 1–8; Pl. 7, Figs 1–6

Diagnosis. Small- to medium-sized thecideide brachiopod (maximum size = 4.0 mm, Table 3 ). Female shells larger than male shells and with a more complete ontogenetic development. Shell whitish, ventribiconvex, slightly uniplicate anteriorly. Ventral valve with short, triangular, convex pseudodeltidium, anterior part with numerous irregular cavities. Sulcus present in most specimens. Ventral valve floor median ridge absent. Hemispondylium formed by two pointed lateral prongs and a prominent median myophragma; supporting structure of hemispondylium absent in adults. Dorsal valve with narrow and straight median ramus with subparallel frilled margins; ramuli relatively narrow, slightly curved, with spiny margins; ventral side of ramus and ramuli weakly convex. Anterior median depression reduced, narrow, anterior margin tuberculated. Minor interbrachial lobes often asymmetrical, straight, short, subparallel, never furcated. Major interbrachial lobes relatively thin with dentate outer margins. Lophophore ptycholophous.

Etymology. The name is directly derived from the word “ mutiara ”. In Indonesian language “ mutiara ” means “pearl”. This is the name of the shipwreck where the new species was discovered.

Type material. Holotype: RBINS-RI-BRA 24 (Plate 3, Figures 4a and 4b), fully grown mature female specimen with marsupial notch, specialised tentacles and median brood pouch with larvae. Paratypes: RBINS-RI- BRA 21-22, 25, 27, 33, 39, 42, 49, 52, 54. The type material is deposited in the Belgian Royal Institute for Natural Sciences (RBINS).

Type locality. Shipwreck “ Mutiara ”, water depth: 30 m, Bay of Palu, off Donggala Harbour, Donggala near Palu, Province of Central Sulawesi, Indonesia.

Additional material. Sediment samples from shipwreck, 78 entire shells, 53 dorsal valves and 47 ventral valves; samples picked from metal wall of shipwreck, air-dried, 242 adult specimens, 215 juvenile specimens and 69 ventral valves; specimens picked from metal wall of shipwreck, preserved in ethanol, 115 entire adult shells and 92 entire juvenile shells; ZMB Bra 2264-2265, pieces of metal wall with specimens of M. cf. minuta and O. mutiara n. sp.

1 specimens with marsupial notch; 2 specimens lacking marsupial notch.

Description. External shell characters: The endopunctate shell is relatively small for the genus ( Table 3 ), reaching a width of about 3 mm, variable in shape ( Table 3 ). The maximum width (W) is at the mid-dorsal valve (Pl. 3, Fig. 1a). The value of the length to width (L/W) ratio increases during growth and the shells become slightly longer than wide (Text-Fig. 3). The whitish shell has an irregularly elongate shape and is cemented to the substrate by the posterior and ventral part of the ventral valve. Due to this type of attachment, the posterior part of the shell is often truncate and can be distorted. The shell is strongly ventribiconvex (Pl. 3, Fig. 1b), the dorsal valve being relatively flat, lid-like, except for its median part which is slightly convex. During growth the thickness of the shell increases relatively to its width, as indicated by the changing thickness to width (T/W) ratio (Text-Fig. 3). A median low sulcus can develop at the anterior margin of the ventral valve (Pl. 3, Fig. 2b) resulting in a slight cordiform shape of the dorsal valve. The entire shell is lifted from the substrate anteriorly (Pl. 3, Fig. 1c), its anterior part tending to be in a more elevated position than its posterior part. Such a geniculation of the ventral valve is common in thecideide brachiopods as already illustrated by Pajaud (1970; p. 219, fig. 130A). The anterior commissure is variable, rectimarginate to slightly uniplicate or sometimes slightly unisulcate. The lateral commissure is gently concave dorsally.

The ventral valve has a short but strongly produced beak with a flat triangular interarea ornamented with numerous fine regular growth lines parallel to the hinge line. A raised triangular, transversely convex pseudodeltidium is developed (Pl. 3, Fig. 7). The pseudodeltidium is relatively long, representing till 25 % of total shell length and has irregular growth lines on its surface (Pl. 3, Fig. 7). The anterior part of the pseudodeltidium is perforated by numerous irregular cavities which do not represent punctae (Pl. 3, Fig. 7–8). Irregular growth lines are visible on the external ventral shell surface (Pl. 3, Fig. 1b).

TEXT-FIGURE 3. Scatterplots of morphometric measurements of Ospreyella mutiara n. sp. specimens. L: length (mm); W: width (mm); LDV: length of dorsal valve (mm); T: thickness (mm); WH: length of hinge line (mm). Relationships between ratios L/W and width; LDV/W and width; T/W and width; WH/W and width. Linear regression applied when significant and correlation coefficient (r) indicated.

The lid-like dorsal valve is always wider than long, subrectangular (Pl. 5, Fig. 1a) to transversely ovate (Pl. 5, Fig. 5a) in shape with an emarginated anterior commissure. The dorsal valve in larger specimens is subrectangular (Pl. 5; Figs 1a, 2a, 3a), whereas the dorsal valve in smaller specimens is more transversely ovate (Pl. 5; Figs 5a, 6a). This variability in shape is related to the size of the specimen as the value of the length of the dorsal valve to width (LDV/W) ratio (Text-Fig. 3) does not change throughout growth. The dorsal valve surface exhibits irregular growth lines. The surface of the prominent protegulum (if preserved) is wrinkled. The hinge line is straight and always narrower than the maximum width of the valve ( Table 3 ). Its length represents 55 % (mean value) of the maximum width of the shell. However, the length of hinge line can increase up to 83% of the width of the shell ( Table 3 ). In fact, in comparison with the maximum width of the shell, the length of the hinge line increases during growth as indicated by the values of the width of the hinge to the width of the shell (WH/W) ratio (Text-Fig. 3).

Internal shell characters: The cordiform or slightly bilobed ventral valve has a roughly striated surface valve floor without a median ridge and exhibits large and irregular endopunctae (Pl. 3, Fig. 5a). The commissure is limited internally by a row of more or less regular, strong tubercles, and externally a smooth rim is developed. The cyrtomatodont strong teeth are short and relatively thick and covered with secondary shell material. Their surface is corrugated. The hemispondylium consists of two pointed lateral prongs and a prominent median myophragma (Pl. 3, Fig. 5b). A supporting septum of the hemispondylium cannot be observed in adult or young specimens. However, in juveniles a temporary very small supporting structure is developed in a few cases (“s.s.” in Pl. 6, Fig. 7b). No median ridge is present in the ventral valve. Two calcitic oval pads covering the gonads are clearly visible in the posterior part of the ventral valve floor (“GP” in Pl. 3, Fig. 4a). In large (“female”) specimens a median brood pouch containing several larvae (“L” = larvae in Pl. 3, Fig. 4a) is situated between these gonad pads.

In the dorsal valve the subperipheral rim is heavily papillose, with strong irregular tubercles. These tubercles are generally ornamented with striated secondary shell fibres on their tips (Pl. 5, Fig. 7). A very narrow smooth flange is present along the commissure. The dental sockets are strong and formed by a thick, curved inner socket ridge and a flat depressed outer socket ridge (Pl.5, Fig.1c). The trilobed cardinal process (Pl. 5, Fig. 3c) is wide, massive but relatively short and slightly curved dorsally. The development of the median lobe is variable as it appears sometimes very prominent (Pl. 5, Fig. 1h) or sometimes rather weak (Pl. 5, Fig. 3g). Shell structures developed in the dorsal valve are raised towards the posterior part of the valve (Pl. 5, Figs 1c, 2c, 3f, 5c). A thin and relatively narrow brachial bridge (Pl. 5, Fig. 1h) is built by the fusion of the posterior parts of the inner rim margin (similar to a fusion of crural processes as proposed by Logan 2008, p. 411). This brachial bridge remains complete in small specimens (Pl. 5, Figs. 5e, 6d) but is interrupted in larger specimens by a prominent marsupial notch (Pl. 5, Figs 1h, 2d, 3h). The marsupial notch is a small circular hole open on its ventral side. The posterior face of the marsupial notch exhibits a small platform with a small convex median ridge prolonged by a small pointed spur (Pl. 5, Figs 1h, 4a, 4b). The inner surface of the marsupial notch exhibits the muscle scars of the specialized filaments. Between the cardinal process and the brachial bridge a heart-shaped visceral foramen (Pl. 5, Fig. 1h), free of a calcitic pole, is apparent. On each side of the visceral foramen, on the posterior part of the inner rim margin, the PLATE 3. Ospreyella mutiara n. sp. Size of the specimens indicated with scale bars.

Fig. 1. RBINS-RI-BRA 21, paratype. This fully grown adult is still attached to the substrate. 1a: Dorsal view. 1b: Anterior view showing the ventribiconvex shell. 1c: Oblique lateral view. The shell is curved upwards and is more elevated in its anterior part. Irregular growth lines are visible.

Fig. 2. RBINS-RI-BRA 22, paratype. Young specimen attached to the substrate (shell of Neopycnodonte ). At this stage of growth the shell is mainly attached by the posterior ventral side of the ventral valve. 2a: Dorsal view. The pseudodeltidium and the prominent protegulum with its wrinkled surface are clearly visible. 2b: Anterior view. A weak sulcus in the anterior part of the ventral valve is visible. 2c: Oblique lateral view.

Fig. 3. RBINS-RI-BRA 23. A piece of metallic substrate from the store in the shipwreck with several juvenile specimens of O. mutiara n. sp. (arrows) 3a: Overview. 3b: Detailed view of two juvenile specimens attached to the substrate. At this stage of growth, the posterior part of the ventral valve is very prominent. 3c: Detailed view of one juvenile specimen. The pseudodeltidium exhibits irregular cavities at its anterior margin. The surface of the protegulum is wrinkled. Fig. 4. RBINS-RI-BRA 24, holotype. The specimen is an adult specimen with a median brood pouch and larvae (L). Critical point dried. 4a: Opened complete articulated specimen showing the lophophore in living position. Specialized tentacles are located at the posterior part of the lophophore. 4b: Dorsal view of ventral valve showing detached fibres of the adductor and diductor muscles in the posterior part of the specimen. Two calcitic oval pads cover the gonads in the visceral cavity. Exposed larvae are visible between the calcitic pads in the posterior part of the valve.

Fig. 5. RBINS-RI-BRA 25, paratype. Adult ventral valve attached to the substrate. The two calcitic oval pads covering the gonads are missing. 5a: Dorsal view showing the peripheral ridge, the surface of the valve floor, the interarea, the pseudodeltidium and one tooth. The left tooth is broken. 5b: Detailed view of the hemispondylium which consists of two pointed lateral lobes and a prominent median myophragm.

Fig. 6. RBINS – RI – BRA 26, paratype. Juvenile ventral valve attached to the substrate. The sculptured surface of the anterior part of the pseudodeltidium is very apparent. The ventral valve is coalesced with the substrate.

Fig. 7. RBINS-RI-BRA 27, paratype. Dorsal view of the posterior part of the ventral valve. The interarea exhibits fine sub-parallel growth lines. The pseudodeltidium is convex. The hinge line is straight. The prominent protegulum exhibits a wrinkled surface.

Fig. 8. RBINS-RI-BRA 22, paratype. Dorsal view of the pseudodeltidium and the hinge line of the ventral valve.

reniform lateral adductor muscle scars are clearly visible (Pl. 5, Figs 1d, 2d, 3g, 5d, 5c). The diductor muscle scars are sometimes visible on the posterior margin of the cardinal process (Pl. 5, Figs 1h, 5d) but they are often poorly defined. The median adductor muscle scars are present in the visceral cavity on either side of the visceral foramen (Pl. 5, Fig. 1f). The margins of the intrabrachial ridges exhibit short strong spines. Underneath the intrabrachial ridges a pair of residual small holes (Pl. 5, Fig. 1a) is present which is filled by shell material in most adults during growth (Pl. 5, Fig. 2a). The outer margins of the major interbrachial lobes are connected to the jugum (Pl. 5, Fig. 1g) and exhibit dentate margins. The two subparallel minor interbrachial lobes are relatively short, thick and never divided or furcated in any specimens observed. The development of the minor interbrachial lobes is often asymmetrical (Pl. 5, Figs 2a, 3a). The pointed median ramus has a slightly concave upper surface, subparallel and frilled lateral margins and is connected posteriorly by the small jugum (Pl. 5, Fig. 1g) to the intrabrachial ridges. The length of the median ramus is variable and terminates in the middle of the valve or sometimes at about twothirds of the valve length. The median ramus is attached to the valve floor by a triangular base developed in the anterior part of the valve (Pl. 6, Figs 5b, 6b, 6c). Two strong lateral ramuli are well-developed. Each ramulus is relatively narrow but as wide as the median ramus and their upper surface is slightly concave. The lateral margins of the ramuli are ornamented with four to six strong spines on both sides. The concavity of the upper surface of the ramuli tends to decrease with progressive growth. In most adult stage the concavity observed is rather weak as shell material fills this cavity progressively during growth (Pl. 5, Fig. 3c). A narrow median anterior depression is developed, its anterior margin being invaded by strong tubercles. Sometimes, this median depression is absent (Pl. 5, Fig. 2a). This is especially observed when the growth of the anterior part of the valve is disrupted (Pl. 5, Fig. 3a).The ascending apparatus and the descending apparatus can be developed symmetrically (Pl. 5, Fig. 1a) but frequently a strong dissymmetrical development of the dorsal valve structures is observed (Pl. 5, Fig. 2a). The adult PLATE 4. Ospreyella mutiara n. sp. Size of the specimens indicated with scale bars.

Fig. 1. RBINS-RI-BRA 28, paratype. Very early juvenile stage with a trocholophe lophophore possessing 27 tentacles. Lateral adductor and median adductor muscles visible on the left side of the shell.

Fig. 2. RBINS-RI-BRA 29, paratype. Early juvenile stage with a schizolophe lophophore possessing 48 tentacles. The median ramus precursor is developed.

Fig. 3. RBINS-RI-BRA 30, paratype. Juvenile with schizolophe lophophore consisting of 55 tentacles. The median ramus is widening. Detached lateral adductor and median adductor muscle fibres are visible.

Fig. 4. RBINS-RI-BRA 31, paratype. Developmental stage with ptycholophe lophophore. Detached lateral adductor and median adductor muscle fibres are visible.

Fig. 5. RBINS-RI-BRA 32, paratype. Specimen considered as “male” with further developed median ramus and ramuli. A marsupial notch is missing.

Fig. 6. RBINS-RI-BRA 33, paratype. One of the largest specimens with male features. No marsupial notch is apparent. 6a: Ventral view. 6b: Oblique anterior view pointing out the narrow median anterior depression. 6c: Oblique lateral view. 6d: Posterior view. The brachial bridge exhibits no marsupial notch. 6e: Detailed view of the entire median portion of the brachial bridge.

Fig. 7. RBINS-RI-BRA 34, paratype. One of the smallest specimens with female features. This specimen considered as “female” possesses a brooding apparatus. Two larvae are attached to the specialized tentacles, which are removed from the median brood pouch in the ventral valve. 7a: Ventral view. The median ramus and the ramuli are further developed than in the largest shell with male features. 7b: Detailed view of the larvae attached to the specialized tentacles. Fragments of the broken brood pouch are still covering the larvae.

Fig. 8. RBINS-RI-BRA 35, paratype. Specimen with female features. Three larvae are attached to the specialized tentacles. The median ramus and the ramuli are well developed. 8a: Ventral view. 8b: Detailed view of the marsupial notch with specialized tentacles and attached larvae.

Fig. 9. RBINS-RI-BRA 36, paratype. A larger specimen with female features. Marsupial notch and specialized tentacles are present. No larvae are attached to the tip of the tentacles. The tentacles of the lophophore are perfectly spaced by spines on top of the major interbrachial lobe. 9a: Ventral view. Noteworthy is the strong ventral concavity of the ramuli at this stage of growth. 9b: Oblique lateral view. The narrow smooth flange running along the outer margin of the valve is perfectly preserved in this sample. 9c: Oblique anterior view with lifted median ramus and ramuli. The anterior median depression is inconspicuous. 9d: Posterior view.

Fig. 10. RBINS-RI-BRA 37, paratype. Fully grown specimen with female features. The median ramus is uplifted and exhibits a very narrow concave crest. The anterior median depression is inconspicuous. 10a: Ventral view. 10b: Detailed anterior view of the marsupial notch with specialized tentacles. 10c: Detailed posterior view of the marsupial notch with specialized tentacles.

lophophore is ptycholophous with 140/150 tentacles observed in an adult female specimen (Pl. 4, Fig. 9a). Male specimens are smaller and their lophophore consists of a lower number (± 50) of tentacles (Pl. 4, Fig. 6a). The lophophore is attached to the lophophore groove which follows the internal side of the peribrachial ridge, the external sides of the ramuli and the lateral sides of the median ramus (Pl. 5, Figs 3b, 3d). Lophophore muscle scars are parallel and clearly defined. At the trocholophe stage, the lophophore possesses 27 tentacles (Pl. 4, Fig. 1) but this number increases rapidly and 46 tentacles are observed in a young schizolophe developmental stage (Pl. 4, Fig. 2). In smaller adult specimens, the lophophore is developed regularly (Pl. 4, Fig. 6a). In larger adult specimen (females), the lophophore is interrupted posteriorly, allowing the development of a pair of specialized median tentacles (Pl. 4, Figs 7a, 8a, 9a, 10a).

Remarks. A comparison of morphological characters which vary between accepted Ospreyella species is given in Table 4. A detailed comparison of O. mutiara with unidentified Ospreyella species from Lizard Island and New Caledonia is given below.

PLATE 5. Ospreyella mutiara n. sp. Size of the specimens indicated with scale bar.

Specimens with female features:

Fig. 1. RBINS-RI-BRA 38, paratype. A subrectangular valve with two symmetrical minor interbrachial lobes of equal length. 1a: Ventral view. 1b: Oblique anterior view. The two ramuli are still relatively incised and they exhibit spiny margins. The median depression is reduced and quite shallow. 1c: Oblique lateral view. The minor interbrachial lobes are rather wide. Parallel lophophore muscle scars are clearly visible. 1d: Posterior view. The brachial bridge is narrow and exhibits a marsupial notch. The cardinal process is trilobed. The reniform lateral adductor muscle scars are well defined. 1e: Oblique latero-posterior view. 1f: Detailed oblique latero-posterior view showing the brachial bridge with marsupial notch, the cardinal process and the sockets. 1g: Detailed oblique antero-posterior view illustrating the anterior structure of the marsupial notch, the jugum and anterior structure of intrabrachial ridges. 1h: Detailed posterior view of the cardinal process and the brachial bridge with marsupial notch. The marsupial notch is a small platform with a small convex median bridge prolonged by a small pointed spur. The inner surface of the marsupial notch exhibits muscle scars of the tentacles muscle fibres.

Fig. 2. RBINS – RI – BRA 39, paratype. A subrectangular valve with strongly asymmetrical structure and with a development of two very unequal minor interbrachial lobes. The median ramus grew obliquely because the unusual development of the right ramulus was more rapid in this ontogenetic process. The median depression is nearly absent in this specimen. 2a: Ventral view. 2b: Oblique anterior view. 2c: Oblique lateral view. 2d: Oblique posterior view. Fig. 3. RBINS-RI-BRA 40, paratype. A subrectangular valve with slightly asymmetrical minor interbrachial lobes. The anterior part of the valve is modified which is supposedly caused by environmental influence. The growth has been impaired by a barrier on the substrate. The median depression is inconspicuous. The narrow smooth commissural flange is now located near the anterior part of the median ramus. The space between this flange and the median ramus is heavily tuberculated. 3a: Ventral view. 3b: Oblique anterior view. 3c: Oblique latero-posterior. 3d: Detailed view of a minor interbrachial lobe and associated ramulus. 3e: Oblique anterior view showing the modification of the anterior part of the shell. 3f: Oblique lateral view. 3g: Oblique posterior view. 3h: Detailed oblique anterior view of the marsupial notch and of jugum. 3i: A detailed ventral view of the median ramus and ramuli.

Fig. 4. RBINS.-RI-BRA 41, paratype. A detailed illustration of the marsupial notch. 4a: Oblique antero-posterior view. The brachial bridge is interrupted medially by an incomplete notch which is opened ventrally. A longitudinal median ridge is perceptible on the platform of the marsupial notch and a relatively long spur is visible. 4b: Oblique posterior view of the same marsupial notch with the specialized tentacles muscle scars.

Specimens with male features:

Fig. 5 – RBINS-RI-BRA 33, paratype. One of the largest specimens found in the material with a transversely ovate dorsal valve. The ontogenetic development has just produced a small median ramus and very short ramuli. The residual holes in the intrabrachial ridges are still large. The brachial bridge is complete without marsupial notch. 5a: Ventral view. 5b: Oblique anterior view. The large spines on the intrabrachial ridges are clearly visible. 5c: Oblique lateral view. 5d: Oblique posterior view. 5e: Detailed oblique posterior view of the visceral gap with complete brachial bridge. Fig. 6 – RBINS-RI-BRA 42, paratypes. A smaller specimen with a transversely ovate dorsal valve and strong asymmetrical shell structure (only one ramulus has been produced here). The ontogenetic development is still less advanced in this specimen. The jugum and the complete brachial bridge are clearly visible. 6a: Ventral view. 6b: Oblique anterior view. 6c: Oblique posterior view showing complete brachial bridge.

Details of shell structure:

Fig. 7 – RBINS-RI-BRA 36, paratype. Tubercles covering the outer shell margin. The tip of the tubercles is ornamented with vertical ridges formed by secondary shell fibres. The number of ridges is relatively variable (the specimen illustrated here is also visible on Pl. 4, Fig. 9).

The Ospreyella specimen from Lizard Island ( Australia) has many juvenile aspects (Hoffmann et al. 2009). However, these specimens seem to be adult as the shell illustrated a mature specimen with a marsupial notch (width: 1.75 mm; Hoffmann et al. 2009, Fig. 4j). In this specific case, this mature specimen (female) did not develop any minor interbrachial lobes. It seems to have shortened its shell development and its morphological structures are even more ephebic than in O. mutiara n. sp.

The material of “ Lacazella ” sp. from New Caledonia dredged at a water depth of 105–110 m (Bitner 2010, Fig. 6) is a collection of dead shells and resembles O. mutiara n. sp. to a large degree. The shape and the size of the shells are very similar. The minor interbrachial lobes are straight, without furcations, and asymmetrical. However, some differences with O. mutiara n. sp. are perceptible. The median depression in “ Lacazella ” sp. is wider and smooth. The ramuli are further developed, wider, strongly incised and their margins are not dentate. In O. mutiara n. sp. the ramuli are quite narrow, not deeply incised and their margins are strongly frilled. It is assumed that “ Lacazella ” sp. is actually a representative of the genus Ospreyella (pers. comm. J. Hoffmann).

PLATE 6. Ontogenetic stages of Ospreyella mutiara n. sp. Size of the specimens indicated with scale bars. Fig. 1. RBINS-RI-BRA 43, paratype. The earliest stage of growth found in this study. The cardinal process is bilobed and very short. Lateral adductor muscle scars already visible. The brachial bridge is incomplete. The valve floor is smooth. 1a: Ventral view. 1b: Oblique lateral view. 1c: Oblique anterior view. 1d: Oblique posterior view. Fig. 2. RBINS-RI-BRA 44, paratype. Early juvenile stage of growth with complete brachial bridge. The V-shaped structure is made of two separate spikes emerges in the middle of the valve floor. The peribrachial ridge is well-defined in the posterior part of the shell, whereas the lateral parts of the peribrachial ridge are represented only by single tubercles. 2a: Ventral view. 2b: Oblique lateral view. 2c: Oblique anterior view. 2d: Oblique posterior view. Fig. 3. RBINS-RI-BRA 45, paratype. At this stage of growth the cardinal process is trilobed and the two spikes in the middle of the valve floor are fused at their base. The brachial bridge is entire. The peribrachial ridge is defined by a row of fused tubercles. 3a: Ventral view. 3b: Oblique antero-lateral view. 3c: Oblique anterior view. 3d: Oblique posterior view.

Fig. 4. RBINS-RI-BRA 46, paratype. In this developmental stage the major interbrachial lobes are spreading laterally and turn down anteriorly building the first stage of the “apparatus descendens”. A median structure, made of two smooth ridges, is emerging on the valve floor at the base of the joined spikes. 4a: Ventral view. 4b: Detailed ventral view of the joined spikes. 4c: Oblique anterior view. 4d: Oblique antero-lateral view. 4e: Oblique lateral view. The median ridges are clearly visible. 4f: Oblique posterior view with the intrabrachial ridges, the slender brachial bridge and the lateral adductor muscle scars. 4g: Detailed oblique posterior view. 4h: Detailed oblique lateral view.

Fig. 5. RBINS-RI-BRA 47, paratype. In this growth stage the median ramus precursor emerges from the anterior part of the median ridges. A second trianglular structure appears with its base against the two central spikes and its top against the median ramus precursor (present as a knob). 5a: Ventral view. 5b: Detailed ventral view of the median ramus precursor. 5c: Oblique antero-lateral view. 5d: Oblique anterior view. 5e: Detailed oblique anterior view. 5f: Detailed lateral view of the major interbrachial lobe. 5g: Oblique posterior view.

Fig. 6. RBINS-RI-BRA 48, paratype. At this stage of growth the peripheral tubercles are more or less fused and form an elevated tuberculated peribrachial ridge. Pointed processes are secreted from the central part of the interbrachial lobes reaching towards the pointed processes secreted from the spoon-like structures. The median ramus is now a wide triangle and fuse between the interbrachial lobes at the jugum. 6a: Ventral view. 6b: Oblique lateral view. 6c: Oblique anterior view. 6d: Detailed view of the pointed processes. 6e: Oblique posterior view. 6f: Detailed view of the jugum and the brachial bridge.

Fig. 7. RBINS-RI-BRA 49, paratype. An articulated specimen with a complete jugum. The hemispondylium is visible in the ventral valve. 7a: Ventral view. 7 b: Detailed view of the hemispondylium. At this stage of growth the hemispondylium is attached to the ventral valve floor with a very small supporting structure (s.s.). This supporting structure is resorbed in later stages of growth. 7c: Detailed view of the intrabrachial ridges, the major interbrachial lobes and the precursor of the median ramus.

Fig. 8. RBINS-RI-BRA 50, paratype. Detailed ventral view of a specimen with reduced residual holes in the intrabrachial ridges.

Tables

TABLE 3. Ospreyella mutiara n. sp. Morphometric measurements were taken from 44 specimens extracted from the sieved sediments exhibiting a marsupial notch and 14 specimens with male features collected alive in the wreck lacking a marsupial notch. L: length (mm); W: width (mm); T: thickness (mm); LDV: length of dorsal valve (mm); WH: width of the hinge line (mm). L / W = ratio length to width, T / W = ratio thickness to width, LDV / W = ratio length of dorsal valve to width, WH / W = ratio width of hinge line to width. n. m.: value not measured.

“Female” specimens1 L[mm]	W[mm] T[mm]	LDV[mm] WH	L/W	T/W	LDV/W	WH/W
Holotype RBINS - RI -BRA 24 2.4	2.8 1.6	1.8 1.34	0.86	0.57	0.64	0.48
Paratype RBINS - RI - BRA 39 2.6	3.0 n.m.	2.4 2.09	0.87	n.m.	0.81	0.70
Paratype RBINS - RI - BRA 27 3.1	3.0 1.9	2.1 1.7	1.04	0.65	0.71	0.58
Paratype RBINS - RI - BRA 25 2.6	2.7 n.m.	1.8 1.4	0.95	n.m.	0.66	0.53
Paratype RBINS - RI -BRA 54 3.2	3.2 n.m.	2.3 2.2	0.98	n.m.	0.70	0.68
Paratype RBINS - RI - BRA 21 3.0	3.0 1.9	2.2 1.9	1.01	0.63	0.72	0.63
Paratype RBINS - RI - BRA 22 2.4	2.8 1.6	1.9 1.4	0.87	0.58	0.68	0.50
N ♀ (Total) 44	44 41	44 44	44	41	44	44
N (collected alive) 13	13 10	13 13	13	10	13	13
N (dead shells in sediment) 31	31 31	31 31	31	31	31	31
MIN 2.4	2.7 1.3	1.8 1.3	0.83	0.40	0.58	0.44
MAX 4.0	3.9 2.4	2.6 2.7	1.18	0.80	0.81	0.83
MEAN 3.2	3.2 1.9	2.2 2.0	1.02	0.59	0.69	0.63
Standard error ±0.06	±0.04 ±0.05	±0.03 ±0.05	±0.02	±0.02	±0.01	±0.01
“Male” specimens2 L[mm]	W[mm] T[mm]	LDV [mm] WH	L/W	T/W	LDV/W	WH/W
Paratype RBINS - RI - BRA 33 2.3	2.7 n.m.	1.8 1.5	0.87	n.m.	0.68	0.54
Paratype RBINS - RI - BRA 52 1.9	2.2 n.m.	1.6 1.0	0.85	n.m.	0.71	0.45
Paratype RBINS - RI - BRA 49 1.7	2.0 n.m.	1.4 1.0	0.86	n.m.	0.71	0.48
Paratype RBINS - RI - BRA 42 n.m.	2.1 n.m.	1.6 0.9	n.m.	n.m.	0.79	0.43
N ♂ (Total) 14	16 9	16 16	14	9	16	16
N (collected alive) 11	13 6	13 13	11	6	13	13
N (dead shells on Neopycnodonte ) 3	3 3	3 3	3	3	3	3
MIN 1.7	2.0 0.5	1.4 0.7	0.81	0.18	0.60	0.35
MAX 2.7	3.0 1.7	2.2 2.0	1.00	0.64	0.90	0.70
MEAN 2.3	2.4 1.0	1.7 1.3	0.9	0.36	0.73	0.52
Standard error ±0.09	±0.14 ±0.15	±0.10 ±0.05	±0.02	±0.06	±0.02	±0.03