Abstract
Octomeris is a chthamalid intertidal barnacle with eight shell plates. There are currently two species of such barnacles: O. brunnea Darwin, 1854 (type locality in the Philippines), common in the Indo-Pacific region, and O. angulosa Sowerby, 1825, only recorded in South Africa. Octomeris intermedia Nilsson-Cantell, 1921, identified from the Mergui Archipelago in Myanmar, was considered to be conspecific with O. brunnea by Hiro (1939) based on samples collected in Taiwan. The morphological differences in shell and opercular plates between O. brunnea and O. intermedia are believed to be intra-specific variations due to different degrees of shell erosion. In the present study, the genetic and morphological differentiations of Octomeris in the Indo-Pacific region were examined. This study found two molecular clades (with inter-specific differences) based on the divergence in the COI genes, and the species also have distinct geographical distributions. The Octomeris brunnea clade covers samples collected from the Philippines and Taiwan waters and the other clade, which we argue is O. intermedia, is distributed in Phuket and Krabi, Thailand and Langkawi, Malaysia. Phuket and Krabi are located approximately 300 km south of the Mergui Archipelago, the type locality of O. intermedia. The morphology of samples collected from Thailand fits the type description of O. intermedia in Nilsson-Cantell (1921). Our study concludes that O. intermedia is a valid species based on morphological and molecular evidence.
Highlights
Octomeris is a chthamalid intertidal barnacle with eight shell plates, in contrast to most of chthamalids which have four or six shell plates
Hiro (1939) did not include O. intermedia in the geographical range suggested by NilssonCantell (1921, 1938) (Java and the Mergui Archipelago), nor did the former compare the latter's samples of O. brunnea collected from Taiwan
We conclude that Octomeris intermedia is a valid species using integrative taxonomy
Summary
Octomeris is a chthamalid intertidal barnacle with eight shell plates, in contrast to most of chthamalids which have four or six shell plates. Octomeris intermedia was described by Nilsson-Cantell (1921) from Java (note the erratum on the type locality (South Atlantic Ocean in Nilsson-Cantell, 1921) stated in Nilsson-Cantell (1937); Fig. 1), having a depressed shell and sinuous tergal and scutal margin. Hiro (1939) did not include O. intermedia in the geographical range suggested by NilssonCantell (1921, 1938) (Java and the Mergui Archipelago), nor did the former compare the latter's samples of O. brunnea collected from Taiwan. We collected O. intermedia from Phuket and Krabi, Thailand (300 km south of the Mergui Archipelago) and Langkawi, Malaysia, and O. brunnea from Taiwan and the Philippines; these samples cover different sizes and degrees of erosion. The mitochondrial cytochrome C oxidase subunit I (COI) and 12S rRNA genes were used as genetic markers to test the hypothesis that O. intermedia is an eroded form of O. brunnea in the Indo-Pacific region
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