Supplemental re-description of a deep-sea ascidian, Fimbrora calsubia (Ascidiacea, Enterogona), with an inference of its phylogenetic position

By

Hasegawa, Naohiro
Hookabe, Natsumi
Fujiwara, Yoshihiro
Jimi, Naoto
Kajihara, Hiroshi

Type

Article

Date of Publication

2024

Original Publication

Zoosystematics and evolution

Volume

100

Series / Issue

Issue: 1

Pages

129--140

Subjects

bathyal zone , Biogeography , Chordata , Phylogeny , taxonomy , Tunicata , Urochordata

Contributed by

Pensoft Publishers

Language

English

Published by

Sofia Pensoft

Identifiers

DOI: https://doi.org/10.3897/zse.100.113132

 

Abstract

Fimbrora Monniot & Monniot, 1991, a macrophagous ascidian genus within the family Ascidiidae Adams & Adams, 1858, is currently monotypic, represented by F. calsubia Monniot & Monniot, 1991, a species previously recorded from the bottom of the South Pacific at depths of 1000–1860 m. The taxonomic status of Fimbrora has remained ambiguous because characteristics in its branchial papillae and neural-gland opening are incompletely known in previous studies, while these traits are essential for distinguishing other ascidiid genera. So far, no nucleotide sequence representing F. calsubia is available. In this study, we collected a single specimen of F. calsubia at a depth of 2027 m, about 400 km off the Pacific coast of Honshu, Japan. This is the deepest record, as well as the first report from the North Pacific, for the species. Our examination indicates that Fimbrora is morphologically similar to another ascidiid genus, Psammascidia Monniot, 1962, by having only secondary branchial papillae in the pharynx. Our phylogenetic analysis, based on the 18S ribosomal RNA and cytochrome c oxidase subunit I genes, along with those of 27 ascidian species available in public databases, showed that F. calsubia was more closely related to Ascidia zara Oka, 1935, Phallusia fumigata (Grube, 1864) and Phallusia mammilata (Cuvier, 1815) than to Ascidia ceratodes (Huntsman, 1912), Ascidiella aspersa (Müller, 1776) and Ascidiella scabra (Müller, 1776). Our results also indicated that acquisitions of macrophagous feeding by deep-sea members happened independently at least three times in the evolutionary history of the entire Ascidiacea.