Dendostrea folium ( Linnaeus, 1758 )

Lam, Katherine & Morton, Brian, 2009, Oysters (Bivalvia: Ostreidae And Gryphaeidae) Recorded From Malaysia And Singapore, Raffles Bulletin of Zoology 57 (2), pp. 481-494 : 488-490

Dendostrea folium ( Linnaeus, 1758)

Common name: Foliate oyster ( Fig. 5 )

Ostrea folium Linnaeus, 1758: 699 . Ostrea folium – Born, 1780: 112; Dodge, 1952: 190–191. Dendostrea glaucina Lamarck, 1819: 212 . Dendostrea folium – Swainson 1835: 39. Dendostrea folium – Sowerby 1839: 137: Fig. 181, Iredale, 1939:

402, Pl. 7, Fig. 11; Torigoe 1981: 315–316, 336–337, Pl. 5, Fig.

2, Pl. 26; Harry, 1985: 137–138, Fig. 18; Carriker & Gaffney,

1996: 8; Lam, 2003: 113–114, Pl. 14.

Ostrea (Pretostrea) bresia Iredale, 1939: 396–397 .

Lopha folium – Stenzel, 1971: N1157, Fig. J47.

Material examined. – Type not studied. The type material is in the University Museum , Uppsala, Sweden. This species is not represented in the Linnaean collection of the Linnean Society of London .

Voucher: [ NHM] 20090292, “ Dredged from off Pelangi Beach, ~ 2–3 m, Pulau Langkawi, Malaysia ”, coll. B. Morton, 7 Feb.2004, six individuals preserved in alcohol .

Description. – Shell of medium size, up to 55 mm in height, 30 in length and 10 in width. Outline oval, subequivalve.

Right valve lilac to dark purple externally, left valve white with thin purple stripes. Both valves with dichotomous ribs radiating from the umbones and ending ventrally as either a zig-zagged or rounded undulating margin. Rib tops rounded and bearing obsolete hyote spines at some growth increments. Reddish-purple streaks may radiate from the umbones. Usually, growth squamae on both valves eroded and shell thus often smooth. Attachment area of the left valve extending halfway from the umbo to the ventral margin. Right valve convex left valve attached to hard substratum with “claspers”, which are shelly processes that clasp the twig-like substratum ( Stenzel, 1971).

Commissural shelf not developed. Umbonal cavity shallow, ligament short. Chomata usually either not present or restricted to both sides of the ligament and to half the shell height as small elongate tubercles and corresponding pits. Interior of the shell lustrous white with iridescent bluish green patches particularly along ridges formed by the ribs. Adductor muscle scar either reniform or crescentric and the same colour as the interior of the shell. It is positioned posterior to the centre of the pallial region.

Distribution and Habitat. – Indo-West Pacific, Australia, the Philippines, South and East China Seas, Hainan, Taiwan to Kii Penisula, Japan. Usually shallow, from the sublittoral fringe to 8–10 m; it might extend to 50 m on rocks. Attached to other living sessile bivalves. The specimens collected were attached to the mussel Modiolus micropterus Deshayes, 1836 ( Fig. 4 ).

Remarks. – Sometimes, species of Hyotissa may be confused with Dendostrea folium especially in terms of external shell characters. Internal shell characters are more reliable in distinguishing these two species. For example, the shape of the adductor muscle scar is the most important feature for identification: that of Hyotissa is large and circular while that of Dendostrea folium is crescentric. Species of Hyotissa also have a well-developed commissural shelf and are whitish internally whereas Dendostrea does not have an obvious commissural shelf and internally the basal whiteness is always patterned with dark yellowish green patches showing the position of radial rays. The gryphaeid vesicular microstructure also readily distinguishes Hyotissa .

Figures

Fig. 5. Dendostrea folium (Linnaeus, 1758) from Pulau Langkawi, Malaysia (NHM20090292). A, external view of the right shell valve, B, external view of the left shell valve, C, anterior view of an individual, showing the “graspers” developed to hold on to a Modiolus micropterus shell, D, internal view of the right shell valve and E, internal view of the left shell valve.

Fig. 2. Saccostrea mordax (Gould, 1850) from Pulau Langkawi, Malaysia (NHM20090289). A, external view of the right shell valve, B, internal view of the right shell valve and C, internal view of the left shell valve.

Fig. 4. Planostrea pestigris (Hanley, 1846) from Pulau Langkawi, Malaysia (NHM20090291). A, external view of the right shell valve, B, external view of the left shell valve, C, internal view of the right shell valve and D, internal view of the left shellvalve.