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rhinophores retracted

 

underside

 

crawling

 

possible food?





 
Onchidoris
cf. depressa (Alder & Hancock, 1842)
 
Onchidoris cf. depressa
Maximum size:  4 mm.

Identification:  This is a flattened, firm species with elongate tubercles on its notum and elongate rhinophores with diagonal lamellae. The notum is cream, flecked with brown, and contains obvious spicules (at least when young).

Natural history:  Onchidoris cf. depressa is known from two young animals found in algae washes taken at a depth of  3-10 m (10-32 ft). The washes included both rubble and Halimeda kanaloana and the site was moderately exposed. It may be feeding on a large bryozoan, Schizoporella sp., that is common in the Halimeda beds. (Note 1)

Distribution:  Maui: may also be known from southern Australia and New Caledonia.

Taxonomic notes:  Animals superficially similar to this species were described from England as Onchidoris depressa. Since then, similar animals from southern Australia and New Caledonia were found to be genetically distinct (Gosliner, et. al., 2018). Whether the Hawaiian animals are the same as those from the western Pacific is an open question. It was first recorded in Hawaii from Kenolio Park, Maui by CP on Dec. 5, 2014.

Photo:  CP: 3 mm: Kenolio Park, Maui; Dec. 5, 2014.

Observations and comments:

Note 1:  Colonies of Schizoporella sp. were brushed or shaken during the washes. Also, the orange digestive glands of the animals match the color of the bryozoan colonies (see photo). That suggests they may be eating the Schizoporella sp. in Hawaii.
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