Morphological and molecular data based on the COI gene were used to describe a new species of the colonial ascidian
genus
Pycnoclavella. The new species,
P. stolonialis, is widespread sublittorally in the Irish Sea and also occurs on the
western Irish coast, Wales and eastern England and may be locally common. It has been commonly known as the ‘pin
head’ sea squirt since first recorded from Northern Ireland in 1984 but has not yet been formally described.
P. stolonialis
is the only described species of
Pycnoclavella combining the presence of stolons, peribranchial incubation mode and a
larva lacking an otolith. In addition, it features ca. 10% sequence divergence with the closest species of the genus in our
phylogenetic trees.
P. stolonialis showed intermediate characters between two groups of
Pycnoclavella; the
stanleyi and
the
aurilucens groups. Larval morphology and molecular data supported the inclusion of
P. stolonialis within the
aurilucens group, but the stolonial colony structure is characteristic of the
stanleyi group. This implies that colony
structure may not be a good character for separating these two groups. New information on distribution is given for
P.
atlantica,
P. aurilucens and
P. communis.
