Several tens of specimens of P. vancouverensis have been sampled and studied in the type-locality (Vancouver Island) and vicinities (British Columbia, Canada) and in Misaki, type-locality of P. ijimai. There is no doubt of the synonymy of P. vancouverensis with P. ijimaibecause all the taxonomic characteristics are similar (Emig, 1971, 1971, 1977, 1982).
The larva de P. ijimai has been described in 1964 by Zimmer as Actinotrocha vancouverensis.
Nevertheless, the use of the species name vancouverensis goes on in California, even in the Genbank, leading to confusion among the phoronid species, and recently by Santagata & Zimmer (2002):

Reply to Santagata & Zimmer (2002) ^{a, b, c}:

Actually, the point is not to discute the validity of Phoronis vancouverensis Pixell, 1912, which as been demonstrated as a junior synonym of P. ijimai Oka, 1897 by Emig (1971) but to propose new morphological character(s) to separate both "species", that is the lack in the paper of Santagata & Zimmer (2002). So until such information will be published, using at least the established phylogenetic characters (see Emig, 1985) and a new cladistic analysis, P. vancouverensis remains synonym of P. ijimai because the specimens collected in type-locality of each species cannot be distinguished.

Now about larvae, there is a point that Santagata & Zimmer (2002) have missed: the larva is unknown for three species of Phoronida, Phoronis australis, Phoronopsis albomaculata and Phoronopsis californica.
P. australis occurs in Japan (also near places in which P. ijimai has been collected) and in the western Pacific while the two other species of the "group" (see Emig, 1985), P. hippocrepia and P. ijimai have been recorded in many places of in the Pacific Ocean (see the geographic distribution for each of those species) and in particular along the East coast of America ^a.

The last point but not the least is related to identification of the specimens in Genbank : what are the taxonomic and phylogenetic characters of the listed specimens ?
For Phoronida, I agree that it is a bit difficult because histological slides are required to identify adult specimens. Specimens of various species may also be mixed in soft sediments (see for example ^b and many others have been published by Emig).

^a  One should argue that the recorded phoronid species along the East coast of North and Central America are... all known phoronid species except P. australis ! That are: Phoronis ovalis, P. hippocrepia, P. ijimai, P. muelleri, P. psammophila, P. pallida, Phoronopsis albomaculata, Phoronopsis harmeri, Phoronopsis californica.

^b  See also about Phoronis architecta (synonym of P. psammophila)

^c  See also about Phoronopsis viridis (synonym of Phoronopsis harmeri)

To know more about this synonymy, please read the papers which are cited below.

References

This species, recently described as a new species, appears to be only synonymous with Phoronis ijimai; in fact, the individuals recorded near Van Yên (Vân Dôn district, Quang Ninh province - 21°04'46"N, 107°34'18"E) have the same taxonomic characteristics as described mentioned by Temereva & Neklyudov (2017), including: :

• The biotope shown in Figure 2 to be compared in the album;
• The specific disposition and shape of nephridia (see also Emig, 1982, 1985);;
• The presence of two giant nerve fibers;
• The shape and arrangement of the lophophore and tentacles;
• The muscular formulas to compare with that of P. ijimai, as well as the shape of the longitudinal muscles:

Curiously, Temereva & Neklyudov (2017) do not discuss the validity of this species comparing the taxonomic characters with those of the two closely related species: P. hippocrepia and P. ijimai.

To know more about this synonymy, please read the papers which are cited below.

References

Temereva E. N. & B. V. Neklyudov, 2017. A new phoronid species, Phoronis savinkini sp. n., from the south China Sea and an analysis of the taxonomic diversity of Phoronida [in Russian]. Zoologicheskii Zhurnal, 96 (11), 1285-1308.

This recently described as a new species appears to be Phoronis ijimai during regeneration processes (see also Emig, 1972, 1973, 1982, about regerenation and systematics )

To know more about this synonymy, please read the papers which are cited below.

References

Temereva E. N. & V. V. Malakhov, 1999. A new rock dwelling phoronid species, Phoronis svetlanae (Lophophorata, Phoronida) from the Sea of Japan. Zool. Zhurn., 78 (5), 626-630.

Emig C. C., 2003. Phylum Phoronida. In: Protostomes. Grzimek's Animal Life Encyclopedia, (ed. 2) vol. 2, 491-497.