Talonostrea talonata X.-X. Li & Z.-Y. Qi, 1994

Crassostrea zhanjiangensis X.-Y. Wu, S. Xiao & Z. Yu, 2013

The genus Talonostrea was first defined on morphological characters alone and was then monotypic, the type species T. talonata being described simultaneously by Li and Qi (1994). The oyster took the common name of the ‘cat’s paw oyster’ referring to the folded and broadly digitate margin of the upper valve. This contrasts with T. zhanjiangensis and T. salpinx (described below), where the upper valve is flat with or without narrow fluted extensions. Talonostrea salpinx has the unique feature of possessing trumpet-shaped marginal projections. The shell, therefore, offers few if any defining characters. The anatomical character of a separated style sac observed in T. talonata has not been confirmed in T. zhanjiangensis and at this time, we cannot be sure if this character is an apomorphy of T. talonata or a synapomorphy of the genus as a whole. The anatomical arrangement in T. salpinx (see below) agrees with that of T. talonata as illustrated in Cavaleiro et al. (2019) and therefore does suggest that this is a defining feature of Talonostrea. As the anatomy of T. zhanjiangensis has not been described, the genus Talonostrea is confirmed on molecular data alone (Salvi and Mariottini 2017) but it is possible that the separate style sac/mid gut character will prove to be a synapomorphy of the genus.

All type material deposited in the National Museum of Wales (NMW.Z) Kuwait • 20 + specimens in two clumps; Kuwait Bay, between Ashairij and Umm Al-Namil Island; 29.382423°N, 47.851735°E; intertidal as clumps on rocks and stones; 30 Nov 2019; PG Oliver leg. (Fig. 4). Holotype (Shell h in Fig. 4A–C) Kuwait • 1 shell; same collection data as for preceding; NMW.Z.2021.009.001; lower valve length 39.1mm, upper valve length 33.1 mm. Paratypes (Fig. 4D, to illustrate variation in internal colouration only) Kuwait • 11 specimens used in sequencing; collection data as for preceding; NMW.Z. 2021. 009.002/1–11.

Kuwait • remainder of shells in clumps; same collection data as for preceding; NMW.Z.2021.009.003. Kuwait • 20 + specimens in three clumps; Khor Al-Subiyah, Al Maghasil; 29.74127°N, 48.09567°E; upper intertidal reef forming on beach rock; 15 Nov 2015 and Dec 2019; PG Oliver leg. (Fig. 5). Paratypes. Kuwait • 12 specimens used in sequencing; collection data as for preceding; NMW.Z.2021.009.004/1–12. Paratypes. Kuwait • remainder of shells in clumps; same collection data as for preceding, NMW.Z.2021.009.005 (Fig. 5A, B, E). Kuwait • 50 + specimens; Kuwait Bay, Umm Al-Namil island; 29.38687°N, 47.87075°E; on stones, cobbles and rock in the upper intertidal; 29 March 2021; Manal Al-Kandari leg. Paratypes. Kuwait • 12 specimens; collection data as for preceding; NMW.Z.2021.009.006 (Fig. 6A–C) including shells from dissections.

Kuwait, Kuwait Bay, between Ashairij and Umm Al-Namil Island, 29.382423°N, 47.851735°E, intertidal attached to rocks and cobbles, 30 Nov 2019, PG Oliver leg.

salpinx, Greek, a trumpet; referring to the marginal trumpet-shaped projections typical of this species

(Type series from Ashairij) Maximum size recorded 41 mm. Specimens of all sizes found growing on or among others creating dense clumps. Shells thin but robust. The lower (left) valve openly cupped, umbonal cavity shallow (Fig. 4B). Margins undulating, slightly raised, roundly digitate and occasionally drawn out into blunt spines. The attachment area is large, furnished with spines and foliations. The inner shell layer is white with brown to black pigmented adductor scars.

Upper (right) valve smaller than and fitting into lower valve (Fig. 4A). Rather flat but undulating, nacreous free margin very narrow. Outline variable, mostly oval some irregularly subquadrate to lingulate. External surface often worn smooth, or weakly foliaceous but not raised into commarginal frills. Occasional shells have open trumpet-shaped projections arising from the margins (Fig. 4E); these are formed by convoluted folding and do not form an entire tube. These trumpet-shaped spines are found mostly in small shells in sheltered sites. Hinge relatively narrow, ligament alivincular, amphidetic; dorsal area not greatly elongated. Chomata absent. External colouration mostly obscured by surface algae but pale grey, some with traces of purple radial streaks, these more prominent in small shells (Fig. 4F). The inner shell layer mostly white, inner margin frequently tinged with pale orange and dark grey, crescentic adductor scar mostly black, some brown, some lacking colour except for a dark ventral rim (Fig. 4C, D)

(Paratype series from Khor Al-Subiyah) (Fig. 5A–E) Maximum size recorded 30 mm. Specimens of all sizes forming a continuous reef over beach rock. The shells are thin but not fragile.

The lower valve is deeply cupped often with a deeper umbonal cavity related to the extension of the dorsal hinge plate. Attachment area over most of lower valve with interlocking spines and foliations. Outline is mostly oval but can be distorted into many shapes from lingulate to subcircular; the free margin is upturned, weakly convoluted with short blunt spines; except where growing in sheltered or uncrowded condition where the margins can be greatly extended into spathulate spines (Fig. 5C). Chomata are absent. The ligament is alivincular, the dorsal plate often elongated usually amphidetic but coiling in some. The inner shell layer colour white; adductor scar crescentic reddish-brown to dark brown/black in colour, colouration often extending into the umbonal cavity.

Upper valve smaller than, and fitting into lower valve. Rather flat but undulating, nacreous free margin very narrow slightly elevated. External surface weakly foliaceous but not raised into commarginal frills. Shells sheltered among others and juveniles frequently display open trumpet-shaped projections as above (Fig. 5D). External colouration is mostly obscured by algal growth but is underlying greyish-beige; juvenile shells and those in sheltered positions may have coloured radial bands of a purple-black hue (Fig. 5C). Chomata are absent. The inner shell layer is white with the crescentic adductor scar brown to brown-black in colour (Fig. 5E).

(Paratype series from Umm Al-Namil) (Fig. 6A–D) Maximum size recorded 35 mm. Specimens of all sizes are found attached in clumps (Fig. 6E) to stones and cobbles or encrusting rocks (Fig. 6F). While most of these are identical to the type series (Fig. 6F) those from sheltered sites are rather thin, may have marginal extensions that are easily broken and often exhibit a more vivid colouration.

Attachment area small, free area with 5–7 prominent folds extending as furrowed spines (Fig. 6B). Outline is mostly oval but can be distorted into many shapes from lingulate to subcircular. Chomata absent. The ligament alivincular, dorsal plate often elongated usually amphidetic but coiling in some. The inner shell layer colour white: adductor scar crescentic reddish-brown to dark brown/black in colour, colouration often extending into the umbonal cavity (Fig. 6B).

Upper valve smaller than, and fitting into lower valve. Rather flat but undulating, nacreous free margin narrow, slightly elevated and extended as spines (Fig. 6A) fitting into furrows of lower valve. External surface weakly foliaceous, not raised into commarginal frills. External colouration ranging from uniformly dull grey, dirty white, to beige with purple-brown radial stripes extending onto spines (Fig. 6A); few golden brown (Fig. 6D) to purple-black all over (Fig. 6C). Chomata absent. Nacreous layer white with the crescentic adductor scar brown to brown-black in colour (Fig. 6A).

Anatomy (Fig. 7). Preserved specimens from Umm Al-Namil were opened by severing the ligament, levering the upper valve open slightly and then slicing the adductor muscle to free the upper valve. The animals were then dissected by sequentially removing the mantle (Fig. 7A), the ctenidia and finally dissecting into the visceral mass removing gonad and digestive diverticula tissue to reveal the alimentary system (Fig. 7B). Tissues have been stained in Methyl Blue to aid contrast.

The mantle in its preserved and contracted condition shows an array of radial folds (Fig. 7B). Mantle edge free except at the ventral margin where it is joined to the ctenidium. Mantle edge with three folds, middle fold with short pigmented, tuberculated, tentacles typically arranged with a one large one small pattern (Fig. 7C), inner fold with simple smooth unpigmented tentacles all of equal size and shape (Fig. 7C).

Adductor muscle crescent shaped in a posterior ventral position; pericardium immediately dorsal to it (Fig. 7A). Ctenidium of two reflected demibranchs (Fig. 7A), filamental rods bundled into groups of 10–12 by longitudinal and transverse junctions (Fig. 7F). Labial palps triangular, inner faces entirely with sorting ridges, oral groove smooth, short (Fig. 7E).

Alimentary system (Fig. 7B) of large stomach within visceral mass dorsal of pericardium, surrounded by digestive diverticula; oesophagus enters dorsally; mid gut and style sac open on lower anterior side of visceral mass; style sac long, curving ventrally towards adductor muscle; mid gut running towards the posterior below the stomach and then hind gut travels on the posterior side dorsally before plunging under the stomach, curving ventrally, appearing through the pericardium and running as rectum around posterior of adductor muscle; anus simple slightly elevated (Fig. 7D).

Talonostrea salpinx is an oyster of the upper and middle shores living attached to exposed hard substrates. Extensive oyster growth is seen in Khor Al-Subiyah and the western end of Kuwait Bay. The waters of these localities are highly turbid and often hypersaline (Al-Yamani et al. 2004), the intertidal environment is further stressed by experiencing a summer air temperature maximum of 50°C and a winter minimum occasionally as low as 0°C. The summer salinity at Ashairij has been measured at 47 ppt whereas to the south it is around 45 ppt (Pokavinich et al. 2013). In Khor Al-Subiyah the salinity can be variable depending on the discharge from the Tigris and Euphrates rivers through the Shatt el Arab (Omar and Roy 2014). The indications are that T. salpinx can survive multiple extremes of turbidity, air temperature and salinity.

Talonostrea salpinx has been found or recorded from a number of locations other than that cited in Material examined. The current distribution can be summarised as the south-eastern area of Kuwait Bay, from Raz Kazmah to Umm Al-Namil Island where extensive fields are present, and the oysters are attached to low rocks and loose cobbles. Throughout Khor Al-Subiyah, including Khor Al-Milh adjacent to Warbah Island in the very north of Boubyan, where oysters form intertidal reefs and mounds. It has also been found at an unlisted locality in Iran (see Discussion).

The shell morphology of T. salpinx is in keeping with other crassostreines in lacking any chomata. Unusual for the subfamily is the presence of the trumpet-shaped marginal projections as these are not recorded for any other Indo-Pacific Magallana or Talonostrea nor indeed for any Atlantic Crassostrea (Inaba and Torigoe 2004). The adductor scar is strongly pigmented in the larger shells, a character not shared by T. talonata but present in T. zhanjiangensis.

Talonostrea talonata is known as the ‘cat’s paw oyster’ (Li and Qi 1994; Cavaleiro et al. 2019) due to it having a strongly ridged and digitate upper valve and in this feature is very different from T. salpinx. The only other Talonostrea is T. zhanjiangensis Wu et al. 2013. and here there is greater similarity with T. salpinx in having a weakly undulating cupped lower valve and a rather flat featureless upper valve but lacking trumpet-shaped marginal projections. Due to the more rounded upper valve, T. zhanjiangensis has been given the common name of the “cats ear oyster” (Wu et al. 2013), perhaps T. salpinx should be known as the ‘tufted cat’s ear oyster’ in reference to the marginal projections.

The morphology and molecular results of T. salpinx clearly indicate that this new species belongs to the Pacific cupped oyster lineage, with a closer affinity to the Chinese species of Talonostrea rather than to the more widespread Magallana species. This is supported also in the morphology where both T. salpinx and T. talonata share the character of the style sac and mid gut being separate for most of their lengths while in Magallana and Crassostrea the mid gut and style sac run together. A discrepancy between the route of the mid gut as illustrated by Li and Qi (1994) and that of Cavaleiro et al. (2019) for T. talonata exists. In Li and Qi (1994) the mid gut of T. talonata is shown running to the anterior before curving over the face of the stomach whereas in Cavaleiro et al. (2019), and in T. salpinx, the mid gut runs toward the posterior. Without Chinese specimens to dissect we are unable to tell if the difference is real or an artifact in the illustration by Li and Qi (1994). The detailed anatomy of T. zhanjiangensis has never been described. Torigoe (1981) described the mantle tentacles of the major genera noting that for the inner fold of Crassostreinae the tentacles are arranged in an alternating large-small pattern but in T. salpinx the inner mantle fold tentacles are all of the same size. The mantle tentacle arrangement has not been described for other Talonostrea species. Genetic distance between T. salpinx and the other two Talonostrea species is remarkably high (~20% and ~7% for cox1 and 16S genes respectively). Such a high genetic divergence combined with a unique morphology might justify the assignment of this new species to a distinct genus of Crassostreinae. However, we believe that its assignment to the genus Talonostrea is a more conservative approach as it avoids erecting a monotypic genus. This study emphasizes once again that our knowledge of the evolutionary diversity of oysters is far from complete and that molecular data are essential for a robust taxonomic identification and classification of oyster taxa.