A redescription of Syncarpacomposita (Ascidiacea, Stolidobranchia) with an inference of its phylogenetic position within Styelidae.

Naohiro Hasegawa,Hiroshi Kajihara

doi:10.3897/zookeys.857.32654

Abstract

Two species of styelid colonial ascidians in the genus Syncarpa Redikorzev, 1913 are known from the northwest Pacific. The valid status of the lesser known species, Syncarpacomposita (Tokioka, 1951) (type locality: Akkeshi, Japan), is assessed here. To assess the taxonomic identity of S.composita, we compared one of the syntypes and freshly collected topotypes of S.composita with a syntype of S.oviformis Redikorzev, 1913 (type locality: Ul’banskij Bay, Russia). Specimens of S.composita consistently differed from the syntype of S.oviformis in the number of oral tentacles, the number of size-classes of transverse vessels, and the number of anal lobes. In this paper, S.composita is redescribed as distinct from S.oviformis, and its phylogenetic position inferred within Styelidae based on the 18S rRNA and cytochrome c oxidase subunit I gene sequences. In our phylogenetic tree, Syncarpa formed a well-supported clade together with Dendrodoa MacLeay, 1824. In Syncarpa and Dendrodoa, a single gonad is situated on the right side of the body, which is unique among Styelidae, and thus can be a synapomorphy for this clade.

Highlights

Syncarpa Redikorzev, 1913 is a member of the ascidian family Styelidae and consists of two species, Syncarpa composita (Tokioka, 1951) and S. oviformis Redikorzev, 1913
The two nominal species S. corticiformis Beniaminson, 1975 and S. longicaudata Skalkin, 1957, all from the Northwest Pacific, have been synonymized with S. oviformis by Sanamyan (2000). This genus is defined by the following four characters: i) colonial, with zooids reproducing asexually, ii) a single, well-developed fold is present on each side of the pharynx, iii) a single gonad is situated on the right side of the body, and iv) the gonad has several branches
Syncarpa composita is only known by the original description based on material from Akkeshi, Japan (Tokioka 1951)

Summary

Introduction

Syncarpa Redikorzev, 1913 is a member of the ascidian family Styelidae and consists of two species, Syncarpa composita (Tokioka, 1951) and S. oviformis Redikorzev, 1913. The two nominal species S. corticiformis Beniaminson, 1975 and S. longicaudata Skalkin, 1957, all from the Northwest Pacific, have been synonymized with S. oviformis by Sanamyan (2000) This genus is defined by the following four characters: i) colonial, with zooids reproducing asexually, ii) a single, well-developed fold is present on each side of the pharynx, iii) a single gonad is situated on the right side of the body, and iv) the gonad has several branches. Syncarpa composita is only known by the original description based on material from Akkeshi, Japan (Tokioka 1951) It was originally placed in a new monotypic genus Syndendrodoa Tokioka, 1951, which has been synonymized with Syncarpa by Nishikawa (1995). No member of Syncarpa has ever been placed on a phylogenetic context in any of the previous studies

Objectives

Methods