Chthamalus malayensis Pilsbry, 1916

Pochai, Ashitapol, Kingtong, Sutin, Sukparangsi, Woranop & Khachonpisitsak, Salinee, 2017, The diversity of acorn barnacles (Cirripedia, Balanomorpha) across Thailand's coasts: The Andaman Sea and the Gulf of Thailand, Zoosystematics and Evolution 93 (1), pp. 13-34 : 14

Chthamalus malayensis Pilsbry, 1916 Figure 2 ; Tables 2, 3

Chthamalus malayensis Pilsbry, 1916: 310-311; Hiro 1939: 249-251; Utinomi 1954: 18; Karande and Palekar 1963: 231; Pope 1965: 51-63; Newman and Ross 1976: 42; Dong et al. 1980: 125; Ren 1984: 151-153; Southward et al. 1998: 123.

Chthamalus stellatus : Hoek 1913: 267-269.

Chthamalus challenger : Broch 1931: 53-55; 1947: 5.

Chthamalus antennatus : Rossel 1972: 174, pl. 13, figs. 1-7, pl. 14, fig. 1-5.

Non-type material examined.

Andaman Sea: 3 specimens, Phang-nga province , Takua Thung district, Na Tai beach, 16.V.2015, A. Pochai (BUU16. CH.CM01-03) . 2 specimens, Phuket province , Mueang Phuket district, Ao Yon beach, 15.VII.2015, A. Pochai (BUU16. CH.CM04-05) . 1 specimen, Phuket province , Mueang Phuket district, Panwa beach, 16.VII.2015, S. Khachonpisitsak (BUU16. CH.CM06) . 3 specimens, Phuket province , Katu district, Kalim beach, 15.VII.2015, A. Pochai (BUU16. CH.CM07-09) .

Gulf of Thailand: 2 specimens, Chon Buri province, Ko Si Chang district, Ko Kham Yai beach, 05.VII.2015, S. Khachonpisitsak (BUU16.CH.CM10-11) .

Description.

Peduncle absent; body length 3-10 mm; base membranous. Shell elongated oval/shield-shaped, shell white to grey with 6 plates (1 carina, 2 carinal latus, 2 latus and 1 rostrum), carina bigger than rostrum, parietes symmetrical, calcareous and solid, radii solid, inner surface of parietes smooth and white-grey to pale-violet; orifice kite-shaped. Operculum plates symmetrical, articulation of opercular valves deep, scutum and tergum separable. Tergum smaller than scutum, tergum higher than wide, tergum with 4 distinct crests for lateral depressor muscles. Scutum elongated and triangular, adductor pit deep. Mandible with 4 teeth, lower margin pectinated, three large setae at the edge; cirri I with conical spines; cirri II with multi-cuspidate setae and basal guard.

Distribution.

Chthamalus malayensis is widely distributed in the Indo-West Pacific region. It has been previously recorded in Taiwan, Thailand, China, Philippines, Vietnam, Malaysia, India and Australia ( Jones 2004; Tsang et al. 2008; Tsang et al. 2012). From the previous observation, Chthamalus malayensis presented in both the Andaman Sea (Phuket) and the Gulf of Thailand (Si Chang and Samui Islands) ( Tsang et al. 2012). In this study, Chthamalus malayensis were also found in both coastlines: the Andaman Sea (Na Tai, Kalim, Ao Yon, Panwa) and the Gulf of Thailand (Ko Kham Yai) (Table 2 ).

Remarks.

Chthamalus malayensis has usually 4 crests for lateral depressor muscles while Euraphia hembeli and Euraphia depressa contains distinct 10-12 crests at the tergum and 3 small crests, respectively. The size of Chthamalus malayensis ranges from 3-10 mm similar to Euraphia depressa while that of Euraphia hembeli is much bigger (10-33 mm). In addition, Chthamalus malayensis differs from Euraphia depressa in two main characters diagnosed in this study: shape of external shell and jointing pattern of tergum and scutum. The shape of the external shell of Chthamalus malayensis shows a distinct and rather uniform ribbed surface from the lower region to the apex; on the other hand, Euraphia depressa exhibits smooth surface that is never ribbed. Secondly, marked articulation and sinous jointing of tergum and scutum can be clearly noticed in Chthamalus malayensis while Euraphia depressa shows less articulation. However, these shell morphology is not reliable tool for species identification among Chthamalids; hence, we further investigate arthropodal characters. It is clear that Chthamalus has four teeth on the mandible while Euraphia has three teeth on the mandible. In addition, to further identify Chthamalus into the correct species, setae on cirri I and cirri II were observed. Our specimens of Chthamalids have conical spines on cirri I and multi-cuspidate setae with basal guard on cirri II (Figure 2F ); hence, our specimens are confirmed as Chthamalus malayensis .

Moreover, Chthamalus malayensis distributes above the vertical zonation of Tetraclita population. The overlapping of habitats can be seen among these species and even Chthamalus malayensis were found to attach to Tetraclita at the overlapping regions of high shore and middle shore.

Figures

Figure 2. Chthamalus malayensis collected from Ka Lim beach, Phuket (BUU 16. CH. CM 07). A. Dorsal and ventral view of external shell, B. External (left panel) and internal (right panel) view of tergum (upper panel) and scutum (lower panel), C. External (upper panel) and internal (lower panel) view of shell plates, D-G. Light microscopy on mouthparts, D. Close up of cirri I showing conical spines (↑), E. Cirri II, F. Close up on cirri II showing multi-cuspidate setae with basal guard (↓), G. Mandible with four large teeth. D-G. Scale bars in µm. Abbreviations: c, carina; cl, carinal latus; l, latus; r, rostrum.