Dendostrea folium ( Linnaeus, 1758 )

Lam, Katherine & Morton, Brian, 2004, The Oysters Of Hong Kong (Bivalvia: Ostreidae And Gryphaeidae), Raffles Bulletin of Zoology 52 (1), pp. 11-28 : 22

Dendostrea folium ( Linnaeus, 1758)

Common name: Foliate oyster ( Figs. 5 A-C)

Ostrea folium Linnaeus, 1758: 699 ; Born, 1780: 112; Dodge, 1952:

190-191. Dendostrea glaucina Lamarck, 1819: 212 . Dendostrea folium Swainson 1835: 39 ; 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 (561, 991, 1043). This species is not represented in the Linnaean collection of the Linnean Society of London .

Description. – Shell of medium size, up to 80mm in height. Outline orbicular to oval, subequivalve. Both valves concave with dichotomous ribs radiating from the umbones and ending ventrally as either a zig-zagged or rounded undulating margin. Rib tops are rounded and bear obsolete hyote spines at some growth increments. There are two colour morphs, i.e. dark yellow and dark purple. Reddish-purple streaks may radiate from the umbones. Usually, the growth squamae on both valves are eroded and the shell is thus often smooth. The attachment area of the left valve extends halfway from the umbo to the ventral margin. Commissural shelf not developed. Umbonal cavity shallow. The ligament is short. Ligamental area not extended. 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. The interior of the shell is lustrous white with iridescent bluish green patches particularly along ridges formed by the ribs. The interior shell margin is the same as that of the exterior. The adductor muscle scar is either reniform or crescentic and the same colour as the interior of the shell. It is positioned posterior to the centre of the pallial area.

Distribution. – Usually shallow sublittoral fringe to 8-10m; might extend to 50m on rocks. Attached to other living sessile bivalves such as fan shells ( Pinna atropurpurea ) and Isognomon ephippium . Indo-West Pacific, Australia, the Philippines, South and East China Seas, Hainan, Taiwan to Kii Penisula, Japan. Hong Kong; shallow sublittoral fringe to 8-10m in Tolo Channel and Mirs Bay.

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 crescentic. 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.

Figures

Fig. 5. Dendostrea and Ostrea from Hong Kong showing external and internal views of the right valves and the internal views of left valves. A-C. D. folium (SBMNH 345717). D-F. D. crenulifera (NHM 20030493). G-I. O. denselamellosa (AM 108985). Scale bar = 20 mm.

Fig. 2. Neighbour-joining tree based on Kimura 2-parameter distances with 1000 bootstraps using COI mtDNA partial sequences (~618 nt) of Crassostrea. The bootstrap percentages supporting each node of the neighbour-joining and most parsimonious trees are indicated above and below the branches, respectively.Only values>70 are shown.The scale represents percentage substitutions.Ostrea chilensis is employed as outgroups. YSO1 to 6, HHW1 to 6 and TT1 to 3 are samples collected from Yung Shue O, Hoi Ha Wan and Tai Tam, Hong Kong, respectively.