Hermissenda opalescens

Location: Six Fathoms, San Diego, California, United States
Date: 2019/11/09
Length: ??mm
Depth: ??m
Water temperature: ??℃

Description

A colourful aeolid with a translucent body marked with orange patches and iridescent blue lines. Numerous orange cerata are clustered along the back, each with a white tip. It grows to about 5 cm. It is distinguished from the similar Hermissenda crassicornis by its cerata, which lack the white longitudinal stripe present in that species.

Distribution

A more southern species of the northeastern Pacific, ranging from Baja California, Mexico, north to about Bodega Bay, central California. Its range overlaps with the more northern Hermissenda crassicornis in central and northern California. It lives on rocky reefs, sandy bottoms and eelgrass beds from the intertidal to the shallow subtidal. The type locality is San Diego, California.

Etymology

The specific epithet opalescens is Latin for “opalescent,” after the shimmering, iridescent blue lines on the body.

Remarks

A voracious aeolid predator. It was long treated as the same species as Hermissenda crassicornis, but a 2016 study recognised the southern eastern-Pacific populations as this distinct species. Western Pacific and Japanese animals belong to yet another species, Hermissenda emurai.