Chthamalus malayensis Chthamalus stellatus Chthamalus challenger Chthamalus antennatus The diversity of acorn barnacles (Cirripedia, Balanomorpha) across Thailand's coasts: The Andaman Sea and the Gulf of Thailand Pochai, Ashitapol Kingtong, Sutin Sukparangsi, Woranop Khachonpisitsak, Salinee Zoosystematics and Evolution 2017 2017-01-11 93 1 13 34 Pilsbry, 1916 Pilsbry 1916 Maxillopoda Chthamalidae Chthamalus CoL Animalia Chthamalus malayensis Sessilia 1 14 Arthropoda species malayensis   Chthamalus malayensisPilsbry, 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, Panwabeach, 16.VII.2015, S. Khachonpisitsak(BUU16. CH.CM06).  3 specimens, Phuket province, Katu district, Kalimbeach, 15.VII.2015, A. Pochai(BUU16. CH.CM07-09).  Gulf of  Thailand: 2 specimens, Chon Buri province, Ko Si Chang district, Ko Kham Yaibeach, 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 malayensisis 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 malayensispresented in both the Andaman Sea (Phuket) and the Gulf of Thailand (Si Chang and Samui Islands) ( Tsang et al. 2012). In this study,  Chthamalus malayensiswere also found in both coastlines: the Andaman Sea (Na Tai, Kalim, Ao Yon, Panwa) and the Gulf of Thailand (Ko Kham Yai) (Table 2).   Table 2.Species list and distribution of acorn barnacles found in ten sampling sites along the coastlines of the Andaman Sea and the Gulf of Thailand. Abbreviations: +, presence; abs, absence. See Table 1for acronyms of sampling sites.    Species Sampling sites  Andaman Sea Gulf of Thailand  AK NT KL AY PW KS SR KK BK HN    Chthamalus malayensis abs + + + + abs abs + abs abs    Euraphia depressa abs abs abs abs abs + abs abs abs abs    Euraphia hembeli abs + abs abs abs abs abs abs abs abs    Newmanella spinosus abs + abs abs abs abs abs abs abs abs    Tetraclita kuroshioensis + + + + abs abs abs + + abs    Tetraclita singaporensis abs + abs abs abs abs abs abs abs abs    Tetraclita squamosa abs abs abs abs abs abs abs abs abs +    Amphibalanus amphitrite + + + + + + + + + +    Amphibalanus reticulatus abs + abs abs abs + + + abs abs    Megabalanus tintinnabulum abs + abs abs abs abs abs abs abs abs   Total number of species  2  8  3  3  2  3  2  4  2  2  Remarks.   Chthamalus malayensishas usually 4 crests for lateral depressor muscles while  Euraphia hembeliand  Euraphia depressacontains distinct 10-12 crests at the tergum and 3 small crests, respectively. The size of  Chthamalus malayensisranges from 3-10 mm similar to  Euraphia depressawhile that of  Euraphia hembeliis much bigger (10-33 mm). In addition,  Chthamalus malayensisdiffers from  Euraphia depressain 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 malayensisshows a distinct and rather uniform ribbed surface from the lower region to the apex; on the other hand,  Euraphia depressaexhibits smooth surface that is never ribbed. Secondly, marked articulation and sinous jointing of tergum and scutum can be clearly noticed in  Chthamalus malayensiswhile  Euraphia depressashows 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  Chthamalushas four teeth on the mandible while  Euraphiahas three teeth on the mandible. In addition, to further identify  Chthamalusinto 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.   Figure 2.  Chthamalus malayensiscollected from Ka Lim beach, Phuket (BUU16.CH.CM07). 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. Moreover,  Chthamalus malayensisdistributes above the vertical zonation of  Tetraclitapopulation. The overlapping of habitats can be seen among these species and even  Chthamalus malayensiswere found to attach to  Tetraclitaat the overlapping regions of high shore and middle shore. 2015-05-16 A. Pochai CH Phang-nga province 3 2015-07-15 A. Pochai CH Phuket province 2 2015-07-16 S. Khachonpisitsak CH Panwa Phuket province Mueang Phuket district 1 2015-07-15 A. Pochai CH Kalim Phuket province Katu district 3 2015-07-05 S. Khachonpisitsak Thailand Ko Kham Yai Ko Si Chang district 2 Chon Buri province