Sakuraeolis gerberina Y. Hirano, 1999

Location: Nodahama, Izu Oshima, Tokyo, Japan
Date: 2016/07/02
Length: 15mm
Depth: 8.0m
Water temperature: 21.0℃

Description

The general ground color is translucent white, with the pale-pink visceral mass clearly visible through the body wall. Oral tentacles and rhinophores are both smooth, with opaque-white distal tips; the oral tentacles are thicker and slightly longer than the rhinophores. The cerata are normally cylindrical with a small pointed tip when relaxed and become lanceolate when irritated. The digestive gland inside each ceras ranges from reddish orange to yellowish orange and shows through the translucent body wall. The most diagnostic feature is a wide subapical ring of opaque-white epidermal pigment capping each ceras. The reddish-orange jaws are visible through the translucent epidermis. Living animals reach 64 mm in length.

Distribution

Known only from Japan. Type locality: Kominato (35°07′N, 140°11′E), Boso Peninsula, Chiba Prefecture. Additional records include Sagami Bay, Yoichi (Hokkaido), Otsuchi (Iwate), and Mukaishima (Inland Sea of Japan).

Etymology

The specific epithet gerberina refers to the flower gerbera (family Asteraceae). The original description states only that the species is "named for the flower, gerbera."

Remarks

The species feeds on the hydroid Solanderia misakiensis, which grows in current-swept and wave-exposed habitats; Sakuraeolis gerberina consumes its polyps and lays its egg masses on the same colony. The egg mass is a thin, white, undulating coil with eggs 80–90 µm in diameter. The colour plate published by Baba 1949 (Plate 45, fig. 155) under the name Hervia japonica represents this species, and several later guidebooks identified it as Sakuraeolis modesta (Bergh, 1880). A 1999 paper re-examined 17 specimens kept under that label and found 15 to be S. gerberina and the remaining two to be the simultaneously described Sakuraeolis sakuracea; neither matches the original description of S. modesta. The Japanese vernacular name "ガーベラミノウミウシ", first proposed in Baba 1949, is retained.