Quite common intertidally under stones on both the Pacific and Japan Sea coasts of Japan.
Shimoda, Izu Peninsula, Sagami Bay, Japan. In tide pool (Depth: 0.3m). 30 Sep 2001. Size: about 8-10mm. Photo: Jun Imamoto.
The skin of Herviella yatsui is translucent clear, with the colours of the viscera showing though. The main colour features of the animal include the head being marked by a black U with the arms extending into the basal half of the oral tentacles. There can also be a short black line on either side of the head beneath the rhinophores. The rhinophores have a black band about halfway along their length and the region above this band is partially or totally pigmeneted white. The dorsal part of the body is covered in irregularly shaped black spots but these are absent from the sides. There are also scattered white spots over the head, dorsum and sides of body. There is a white line or series of spots down the dorsal midline of the posterior foot ('tail').
The cerata have scattered black spots on the dorsal side, usually arranged in two clusters. The upper cluster is usually very dense and forms a black ring near the ceratal tip. The ceratal tip is colourless with a subapical band of white. There can also be a second band of white, or patch of white spots, midway along the cerata. It grows to approximately 15mm in length.
• Baba, K. (1930) Studies on Japanese nudibranchs 3. A. Phyllidiidae. B. Aeolididae. Venus, The Japanese Journal of Malacology, 2(3): 117-125. (Pl.4)
• Baba, K. (1966) The anatomy of Herviella yatsui (Baba, 1930) and H. affinis Baba, 1960 (Nudibranchia - Eolidoidea). Publications of the Seto Marine Biological Laboratory, 14: 1-6,Pls.1-2.
Rudman, W.B., 2001 (October 2) Herviella yatsui (Baba, 1930). [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/hervyats