Two brachiopod Lingula species, L. anatina Lamarck 1801 and L. reevii Davidson, 1880, collected from Japanese waters were compared morphologically and phylogenetically in terms of shell morphology, shell elemental compositions, and 18S rRNA gene sequences. Specimens of L. anatine and L. reevii were collected from Amami-Ohshima Island and Ariake Sea, respectively, and used for comparison. Shells of these species were distinguied by allometric morphology and fresh tissue coloration.
Elemental compositions, as revealed by electron-probe microanalysis (EPMA), of the shells were distinct, too. Higher amounts of sulfur, fluorine and iron were found in the shells of L. anatine, while the L. reevii shells were more enriched with phosphorus, calcium, manganese and magnesium. Layers of calcium phosphate were commonly found in the shell cross-sections of both species, and bromine and iodine were specifically detected in the inter-layer organic matrix. More bromine were present in the L. anatine shells, while more iodine was found in the L. reevii shells.
Comparison of the 18S rRNA gene sequences of L. anatine and L. reevii, along with those from other species registered in a DNA database, resulted in construction of a phylogenetic tree. The two brachiopod Lingula species were placed in two separate clades, which suggests that they be regarded as not-closely related species.