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less white

more white

few papillae

ocelli detail

young, 5 mm


egg mass

(?) sp. #1
Stylocheilus(?) sp. #1
Maximum size:  22 mm.

Identification:  This is a small, translucent-cream sea hare frosted with white and brown flecks. It's decorated with prominent blue and gold ocelli at all sizes. Although superficially similar to Stylocheilus striatus, it can be distinguished from that species by its more prominent blue and gold ocelli, more elaborate villi and brown flecks that are random rather than arranged in lines. The ornateness of the villi and amount of white pigment are variable.

Natural history:  Stylocheilus(?) sp. #1 is a moderately common species found in moderately protected to highly exposed rocky habitats from < 1 to 11 m (< 3 to 36 ft). It may also be found in Halimeda kanaloana beds. It feeds on cyanobacteria (blue-green algae). As in S. striatus, the blue and gold ocelli may represent aposematic coloration "advertising" the presence of toxins concentrated from its food. (Note 1) It lays a tangled, golden-brown egg string that hatches in six to seven days in the laboratory.

Distribution:  Big Island, Maui, Oahu, Kauai and Pearl & Hermes Reef: may be widely distributed in the Indo-Pacific (pending further work to determine whether the Hawaii population is the same as others in the Indo-Pacific).

Taxonomic notes:  Carlo Cunha (pers. com.) suggested that this species may be a Stylocheilus rather than a Bursatella since the latter genus lacks a shell and the widely distributed Bursatella leachii is much larger. (Note 2) However, further work will be needed to confirm the genus. It was first recorded in Hawaii from Maliko Bay, Maui by PF in Aug., 1992.

Photo:  CP: 16 mm:  Ulua Beach, Maui; April 2, 2005.

Observations and comments:

Note 1:  This species, Stylocheilus straitus, other ocellate sea hares that aren't present in Hawaii and most of their various mimics such as Aegires exeches and Scyllae sp. #1 appear highly cryptic from a distance but have very similar blue and gold ocelli when viewed at close range. Perhaps, they're under simultaneous selective pressure from two groups of predators with very different visual systems (maybe, fish and crustaceans such as mantis shrimp?). Together, they seem to represent a large mimicry complex similar to the "black-and-yellow" terrestrial insects (associated with stinging bees and wasps) and including both batesian and mullerian components (maybe, with the sea hares representing the primary models?). As with its terrestrial analog, there are other species in the complex that combine the colors in a less precise manner (such as Stylocheilus longicauda, Dendrodoris krusensternii, Miamira sinuata, Odontoglaja sp. #1 and Lobiger viridis). At least three Hawaiian crab species, the prosobranch Sulcerato sandwichensis, several small fish and the urchin Astropyga radiata (another possible model) may also be involved.

Note 2:  The largest of 99 animals from algae washes was only 22 mm in length and the few animals seen in the field weren't noticeably larger. Also, an 11 mm animal laid eggs while held. This contrasts with 150 to 200 mm for large Bursatella leachii.
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