Nesochthamalus intertextus (Darwin, 1854) Figure 9a-h, Table 1: species no. 52

Chthamalus intertextus Darwin, 1854: 467, pl. 19 figs 1a, b; Dong et al. 1982: 82; Pope 1965: 29, pl. I figs 1f, 3a-d.

Euraphia intertextus: Newman & Ross, 1976: 41; Zevina et al. 1992: 79, fig. 53.

Nesochthamalus intertextus: Foster & Newman, 1987: 326, fig. 3; Southward et al. 1998: 120, fig. 1D, 1H; Chan et al. 2009a: 147, fig. 124.

Material examined.

Ambon Island: 5 specimens, MZB Cru Cir 070, Laha, 3°43'22.5"S, 128°05'02.5"E, coll. P. Pitriana & D. Tala, 7 Sep 2016; 5 specimens, MZB Cru Cir 071, Hila, 3°34'57.5"S, 128°05'31.9"E, coll. Adin, 20 Sep 2017.

GenBank accession numbers.

COI gene (MK995376), 18S (MK981389).

Diagnosis.

Shell depressed with large diamond-shaped orifice; scutum and tergum fused; external radii consist of oblique laminae arising on both sides of the sutures, standing nearly parallel to the parietes, interfolding with each other; cirri II and III with multi-cuspid setae.

Description.

Shell with six plates, oval, flattened, colour of external shell white to pale grey, interior of shell violet; orifice rhomboidal; parietal sutures with conspicuous interlocking pattern (Fig. 9a, b); basis membranous with partial secondary calcification with age; opercular plates fused but separable (Fig. 9c, d); cirrus I with rami unequal; mandible with three large teeth (Fig. 9e), mandibular palp with long setae on exterior basal margin (Fig. 9f); labrum strongly dentate (Fig. 9g). Basal length 8.9-12.1 mm, basal width 6.9-10.3 mm, height 1.3-3.1 mm. Orifice length 3.0-4.9 mm, orifice width 2.6-3.9 mm (measurements for ten specimens are presented in Suppl. material 1: Table S8).

Distribution.

Nesochthamalus intertextus is known from islands in the West and Central Pacific Ocean - Indonesia, New Guinea, Malaysia to Vietnam; China; Taiwan; Philippines; Japan; Hawaii; Pitcairn I (Pope 1965; Newman and Ross 1976; Chan et al. 2009; Jones and Hosie 2016). In this study, N. intertextus was found on Ambon Island at Laha and Hila on stone (a map with the occurrence of Nesochthamalus intertextus in the Moluccas is shown in Suppl. material 1: Fig. S2).

Remarks.

Nesochthamalus intertextus can be distinguished by the conspicuous interlocking pattern exhibited by the parietal sutures and features of the basis, which is membranous in young specimens but becomes secondarily calcified with age, leaving a membranous centre only (Poltarukha 2008; Pope 1965).