A morphological and molecular study of Ligia exotica Roux, 1828 (Crustacea: Isopoda: Ligiidae) from Japan, with descriptions of two new species

Abstract

Ligia exotica Roux, 1828 was originally described based on specimens collected on a ship that came from Cayenne in French Guiana, and has been known to be widely distributed in the world. In Japan this species is the most common in Ligia, and two forms of L. exotica inhabit Osaka Bay, central Japan. To reveal the accurate scientific names of the two forms, we examined not only the detailed morphology but also 16S rRNA and NaK nucleotide sequences, together with L. exotica from another Japanese locality and the related species, L. shinjiensis Tsuge, 2008. As a result, three species, Ligia exotica, L. furcata sp. nov. and L. laticarpa sp. nov., are recognized in four localities, and L. shinjiensis is synonymized with L. exotica. Ligia exotica is characterized by the dentate lacinia mobilis on the right mandible and the appendix masculina lacking a projection. Ligia furcata and L. laticarpa are also characterized by the furcate propodus of the male pereopod 1 and the appendix masculina with an angular projection, and the swollen carpus of the male pereopod 1 and the appendix masculina with a rounded projection, respectively. The three species are distinguishable from one another mainly based on the shapes of pereopods 1–3 in both sexes and the appendix masculina of male. The 16S rRNA analysis confirms the results of the morphological study, and reveals that L. exotica and L. laticarpa also inhabit all over the world (e.g., East Asia, Southeast Asia, India, Africa, the Americas and Hawaii), and China and South Korea, respectively.