American cephalaspidean sea slug now established in Roskilde
Fjord
The non-indigenous cephalaspidean sea slug Haminella solitaria
was discovered for the first time in Danish waters in August 2020.
It was collected near the marina in Kulhuse at the northern end
of Roskilde Fjord in shallow water, where it occurred through
September along with its gelatinous egg masses, In the summer
of 2021 it was found from late July through September, but not in
May or June. Further localities in 2021, Norsminde Fjord (N Belt
Sea), Gyldensteen Lagune (north coast Fyn), Lendrup Lagune
(Limfjord) and Helnæs (SW coast of Fyn) have been obtained
from colleagues in Aarhus, Odense and Roskilde, and a photo-
graphic record of egg masses from the Limfjord indicates that it
has been present since 2018. Haminella solitaria is a Northwest
Atlantic species, which was first observed in European waters in
the summer of 2016 at the Baltic coast of Germany. It is a small
greyish sea slug, called “paper (or glass) bubble-shell”, with a thin,
fragile, white, partly transparent shell, which is almost completely
covered by tissue folds from the head, foot and mantle. The shell
length in specimens from Kulhuse ranged from 4 to 11 mm. Its
egg mass is gelatinous, almost spherical and attached to the sub-
strate by a short stalk.