Aldisa pikokai Bertsch & S. Johnson, 1982

Description

A small dorid nudibranch reaching about 20 mm in length. Body colouration is highly variable, ranging from yellow through orange to bright red, providing close camouflage against the red encrusting sponges on which the slug feeds. The dorsum is covered by a network of sharp longitudinal and transverse ridges, with scattered white speckles on the raised ridges. Three deep, crater-like pits are arranged along the mid-dorsal line, each containing a small dark patch inside. The pits and the reticulate ridges resemble the inhalant ostia and uneven surface of a sponge colony. The mantle margin bears radiating, irregular greyish-white blotches. Rhinophores match the body colour. The gills are red with white markings.

Distribution

Type locality: Oahu Island, Hawaiian Islands. The original description recorded the species from the Hawaiian Islands and from Kwajalein Atoll in the Marshall Islands. Subsequent records extend its range to Japanese waters (e.g. Okinawa), and the species is now considered to occur broadly across the central and western Pacific.

Etymology

The specific epithet is a compound of the Hawaiian words piko (navel; pit) and kai (sea); the species was described from Oahu, Hawaiian Islands.

Remarks

Nocturnal in habit. Feeds on red to orange encrusting sponges on shallow reef substrates, hiding by day and emerging on exposed rock at night to graze. The mid-dorsal pits and reticulate ridges echo the small openings (ostia) and surface texture of its sponge prey, making the slug remarkably cryptic while feeding.

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References

• Aldisa pikokai n. sp., Bertsch H. & Johnson S. (1982). Three new species of dorid nudibranchs (Mollusca, Opisthobranchia) from Hawaii. Veliger. 24(3): 208-218.
• アルディサ・ピコカイ, 小野篤司. (2004). 沖縄のウミウシ. ラトルズ.
• アルディサ・ピコカイ, 中野理枝. (2004). 本州のウミウシ. ラトルズ.
• Aldisa pikokai, Terrence Gosliner, Ángel Valdés and David Behrens. (2015). Nudibranch and Sea Slug Identification Indo-Pacific. New World Pubns Inc.
• ピコチシオウミウシ, 中野理枝. (2018). 日本のウミウシ. 文一総合出版.