(photos of Dirk Schories, Germany: specimens from Sweden and Norway)
Metridium senile is a common species in northern seas. This species is subdivided into several subspecies or variants, although exact status of all forms is not quite clear and requires revision.
Two forms called "dianthus" and "pallidus" are recognized in European seas and at least two species (including Metridium senile fimbriatum and Metridium farcimen) occur in Pacific. On existing underwater photos European form "dianthus" appears to be very similar to Pacific Metridium farcimen, although Pacific specimens may be significantly larger, and the species delimitation in Metridium requires detailed study that should include careful comparison of many specimens collected from different localities.
