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.

The transparency of animals is an important biological feature. Ascidian eggs have various degrees of transparency, but this characteristic has not yet been measured quantitatively and comprehensively. In this study, we established a method for evaluating the transparency of eggs to first characterize the transparency of ascidian eggs across different species and to infer a phylogenetic relationship among multiple taxa in the class Ascidiacea. We measured the transmittance of 199 eggs from 21 individuals using a hyperspectral camera. The spectrum of the visual range of wavelengths (400–760 nm) varied among individuals and we calculated each average transmittance of the visual range as bio-transparency. When combined with phylogenetic analysis based on the nuclear 18S rRNA and the mitochondrial cytochrome c oxidase subunit I gene sequences, the bio-transparencies of 13 species were derived from four different families: Ascidiidae, Cionidae, Pyuridae, and Styelidae. The bio-transparency varied 10–90% and likely evolved independently in each family. Ascidiella aspersa showed extremely high (88.0 ± 1.6%) bio-transparency in eggs that was maintained in the “invisible” larva. In addition, it was indicated that species of the Ascidiidae family may have a phylogenetic constraint of egg transparency.

Nemerteans, or ribbon worms, have been reported from intertidal to hadal depths, often showing bathymetrically wide distribution in genus levels. Although current nemertean systematics practices require to provide DNA sequences and infer phylogenetic relationships with suitable molecular markers, previous molecular systematics on nemerteans are mostly biased toward shallow-water species. Members in the genus Nipponnemertes occur worldwide, from tropical to polar waters and intertidal to bathyal waters. Molecular phylogenetic studies are scarce for the genus; only six shallow-water species of 18 species in the genus were subject to molecular phylogeny. Thus, Nipponnemertes is one candidate that needs to be assessed by genetic approaches. In this study, we performed molecular phylogenetic analyses using 59 specimens in 23 species based on partial sequences of two mitochondrial (16S rRNA and cytochrome c oxidase subunit I) and three nuclear gene markers (18S rRNA, 28S rRNA, and histone H3). Our extensive sampling from intertidal to bathyal waters in the Northwest Pacific significantly updated the fauna of Nipponnemertes in this region from four to 17 species. We herein establish 10 new species and provide an updated species list concisely summarizing all the congeners known from the world. Our phylogenetic tree indicated three major lineages within the genus (herein referred to as “Clade A, B, and C”), each presumably characterized by the combination of morphological characters in the head region. Members in Clade A are: Nipponnemertes pulchra (Johnston, 1837), Nipponnemertes ogumai (Yamaoka, 1947), and several unidentified congeners, characterized by having demarcated head without cephalic patches; members in Clade B are: Nipponnemertes crypta sp. nov., Nipponnemertes jambio sp. nov., Nipponnemertes neonilae sp. nov., and Nipponnemertes ojimaorum sp. nov., species having demarcated head with cephalic patches; members in Clade C are: Nipponnemertes ganahai sp. nov., Nipponnemertes kozaensis sp. nov., Nipponnemertes lactea sp. nov., Nipponnemertes notoensis sp. nov., Nipponnemertes ornata sp. nov., Nipponnemertes sugashimaensis sp. nov., and two unidentified forms collected off Jogashima (Japan) and Guam (USA), species with non-demarcated head lacking cephalic patches. Furthermore, we discuss the evolution of remarkably small body size retained among Clade C.

Members of the family Flabelligeridae are distributed worldwide, inhabiting the underside of rocks or within mixed sand sediments. Some genera of the family have gelatinous tunics with hooked chaetae. The genus Flabelligera Sars, 1829 is one of the members of the gelatinous free-living groups of Flabelligeridae. A fan-shaped cephalic cage, thick gelatinous tunic, and hooked neurohooks distinguish members of this genus. In Japan, Flabelligera affinis Sars, 1829 [Japanese name: Kanten-habouki] has been known as the sole Japanese species of Flabelligera inhabiting several locations. We reviewed Japanese species of Flabelligera from several sites from Hokkaido to Honshu and concluded that the Japanese "F. affinis" contained at least five different species under the specific name. In this study, we described them as five new species. All new species were collected from the underside of rocks in shallow to deep-sea depths. We have also provided mitochondrial cytochrome c oxidase subunit I sequences for DNA barcodes of the new species.