Thordisa bimaculata Lance, 1966

What is the two-spotted dorid?

The two-spotted dorid (Thordisa bimaculata) is a small, velvety dorid nudibranch of the northeastern Pacific, easily recognised by two clusters of dark brown spots on its mantle — one behind the rhinophores and one in front of the gills.

Description

A dorid nudibranch usually about 3 cm long, occasionally reaching around 5 cm. The body colour is variable, ranging from translucent white through pale yellow to orange. The mantle is densely covered with long, tapering papillae, giving it a velvety texture. Its most distinctive feature is a pair of concentrated patches of small dark brown spots — one just behind the rhinophores and the other just in front of the gill circle.

Distribution

Recorded in the northeastern Pacific from California, USA, south to Baja California, Mexico, with most records from the southern California coast. It occurs from the rocky intertidal down to about 30 m.

Etymology

The specific epithet bimaculata is Latin for "two-spotted" (bi-, "two" + macula, "spot"), referring to the two patches of dark spots on the mantle. The common name "two-spotted dorid" reflects the same feature.

Remarks

Like other members of the genus Thordisa, it is thought to feed on sponges.

---

References

• Thordisa bimaculata n.sp., Lance J.R. (1966). New distributional records of some northeastern Pacific Opisthobranchiata (Mollusca: Gastropoda) with descriptions of two new species. The Veliger. 9(1): 69-81.
• Thordisa bimaculata, Chan J.M. & Gosliner T.M. (2007). Preliminary phylogeny of Thordisa (Nudibranchia: Discodorididae), with descriptions of five new species. The Veliger. 48(4): 284-308.
• Thordisa bimaculata, Behrens D.W., Hermosillo A., Fletcher K. & Jensen G.C. (2022). Nudibranchs & Sea Slugs of the Eastern Pacific. Molamarine.