Tridacna noae (Röding, 1798)

Su, Y., Hung, J. - H., Kubo, H. & Liu, L. - L., 2014, Tridacna noae (Röding, 1798) - a valid giant clam species separated from T. maxima (Röding, 1798) by morphological and genetic data, Raffles Bulletin of Zoology 62, pp. 124-135 : 130-131

Tridacna noae (Röding, 1798)

Types. Species figures were provided in Chemnitz, 1784, vol. 7, pl. 49, fig. 494 and McLean, 1947, fig. 12. Since no type material is extant and no types have been designated to date, a neotype of Tridacna noae is hereby designated. The neotype specimen (length 94.4 mm; height 58.4 mm) was collected on 28 August 2007 by Jhih-Hui Hung at Naliao, Green Island, Taiwan. The specimen is deposited in the National Museum of Natural Science, Taiwan, with catalogue number NMNS-6928-001 ( Fig. 6G–L ). The soft body parts were preserved in 70% alcohol. Two additional specimens (NMNS-6928-002, length, 97.9mm; height, 52.5mm and NMNS-6928-003, length, 87.7mm; height, 45.6mm) were collected on 1 November 2008 by Jhih-Hui Hung at Chuanfanshr, Taiwan and the soft body parts were preserved in 70% alcohol.

Description. Shell inflated, strongly inequilateral, usually elongate-ovate. Shell length commonly between 6–20 cm. Umbo markedly anterior in position, margin with a moderately wide byssal orifice. Shell has 5–7 radial ribs, mostly 6, with round to sharp projections on the upper margins. Scales are relatively abundant and the intervals between them on each rib are narrow. In the living animal, mantle colours vary considerably from brilliant to subdued brown yellow, bluish green, blackish blue, blue, and brown. The mantle pattern has one to several obvious layers of oval patches bounded by white margins. Black hyaline organs (eyes) along the border of the mantle are relatively sparse forming a discontinuous line.

Distribution and ecology. Known from northern and Southern Taiwan, Orchid Island, Green Island, Hsiaoliuchiu, Penghu ( Fig. 1 ; Tang, 2005 and this study), Okinawa, and the Ishigaki Islands of Japan ( Kubo & Iwai, 2007). Individuals are attached by a byssus and bore into coral, living in littoral and shallow waters to a depth of 20 m.

Remarks. The shell of this species ( Fig. 6G–L ) is very similar in general appearance to Tridacna maxima (e.g., NMNS- 6928-004, length, 93.0 mm; height, 77.3 mm) ( Fig. 6A–F ). Both species are extremely variable in outline as well as in the number and form of the ribs, and the abundance and shape of the scales. Key characters that distinguish T. noae and T. maxima are the mantle pattern and the appearance/ arrangement of hyaline organs (eyes). Tridacna maxima often has a peripheral-banded pattern with a different colour on the mantle margin. However, the mantle pattern of T. noae is characterised by having one to several obvious layers of oval patches bounded by white margins ( Fig. 7 ). The eyes are concentrated as a continuous line along the mantle margin in maxima but are discontinuous in noae .

Figures

Fig. 6. Shell morphology of Tridacna maxima from Hongchia with prominent rib scales on right valve (A–F) and Tridacna noae from Naliao (G–L). R: rib; S: scale.

Fig. 1. Map of Taiwan showing sampling sites for giant clams.

Fig. 7. Mantle colour pattern and hyaline organs of Tridacna maxima (A, B) and Tridacna noae (C, D). E, Enlarged hyaline organs of T. maxima; F, Enlarged hyaline organs of T. noae. →: Hyaline organs.