Atys semistriatus Pease, 1860

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This species has been observed on Reunion and Mayotte Islands

Order : Cephalaspidea
Superfamily :  Haminoeidea
Family : Haminoeidae
Distribution : Indo-West Pacific
Maximal size (shell) : 17 mm
Abundance :

Species characteristics :

The shell is sculptured all over with finely incised spiral lines except for the centre which is smooth

The shell is transparent white and the head shield and short parapodia have numerous microscopic brown dots

Pink large spots show through the transparent shell which increase in prominence with age

atys semistriatus
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Photo Nathalie Rodrigues
Reunion, Terre Sainte lagoon, less 1 m , December 2014

See more about : Sightening and mating periods

Remarks :

Identification proposed by Nathalie Yonow and Raymond Huet "Atys semistriata seems to me the same as Bulla succisa from "Vie océane" but the form is closer to Bulla than Atys. If we follow Worms, Bulla succisa Ehrenberg, 1831 is a dubious species (taxon inquirendum) and could be Atys semistriata.
    The spelling of the specific name has to be semistriatus (and not semistriata) to agree with the generic name Atys which has been deemed to the masculine
    Synonymous (according worms):
              - Atys semistriata fordinsulae Pilsbry, 1921
              - Atys semistriata mua Pilsbry, 1921                             

Bibliographic data :

Various degrees of brown specking can be found on the headshield and parapodia.
    The parapodia are very thin and only their anterior sections wrap over the front on the shell
    The tail is large and rounded posteriorly
    All species of Atys are herbivores. It is most commonly found at night on algae covered material. During the day they can be occasionally found under rocks or coral rubble
    When the population is high, mating aggregations with copulating pairs can often be seen on top of coral rubble or rocks at night. It lays a spherical, white to pale pink egg mass that is usually anchored in algal turf in the field.

References :

Mollusques de l'île de la Réunion. Collection Jay: Bulla succisa
   Sea Slug Forum Atys semistriata
   Sea Slug of Hawai'i Atys semistriatus

Publications :

Pease, W.H. (1860) Descriptions of new species of mollusca from the Sandwich Islands. Proceedings of the Zoological Society of London, 28 : 18-36.
    Marshall, J.G. & Willan, R.C. 1999. Nudibranchs of Heron Island, Great Barrier Reef - A Survey of the Opisthobranchia (Sea Slugs) of Heron and Wistari Reefs. Backhuys Publishers Leiden

Other photos of Atys semistriatus :


Remy Eudeline

Mayotte, Sakouli, during the night, less 1 m, 30 November 2017



Maurice Jay

Réunion, Shell ref : 298 Collection Maurice Jay

Light and semitranslucent. Ovoid narrowed posteriorly, narrow aperture posteriorly enlarged. The last turn overlooking the turn. Fine spiral furrows on the anterior and posterior thirds, respecting the median part. Less slender silhouette than Atys cylindrica.

White .

Live in the sand from 10 to 70 m. Common enough.

Maximum height 9.9 mm.


Alexandre Laporte

Réunion, Etang Salé on the rocky coast, less 1 m, 24 November 2015, size : 2 mm



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