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Polybranchia orientalis
(Kelaart, 1858)
 
Polybranchia orientalis
Maximum size:  70 mm.

Identification:  This species has broad, thin, leaf-like cerata with serrated edges. The body is cream with white flecks. The cerata are usually edged with white flecks and often have greenish centers.

Natural history:  Polybranchia orientalis is a moderately common species found in the low intertidal and subtidally to depths of 5 m (16 ft). It occurs in highly protected to moderately protected rocky habitats. It's nocturnal but can be found under rocks during the day. When disturbed, it can autotomize its central cerata. (Note 1) According to Kay (1979) the egg mass consists of "cylindrical, transparent, gelatinous coils".

Distribution:  Maui, Oahu and Midway: widely distributed in the Indo-Pacific.

Taxonomic notes:  This is the species listed as Branchophyllum pellucida (Pease, 1860) in Kay, 1979. There is some possibility that animals with and without greenish centers in there cerata are different species. It was probably first reported from Hawaii in Pease, 1860 (as Polybranchia pellucida). It may also be the animal referenced in the text at the bottom of page 185 in Edmondson, 1946.

Photo:  PF: found by CP; Hekili Point, Maui; Sept. 1990.

Observations and comments:

Note 1:  Two animals found in 1985 and 1988 autotomized their central cerata abruptly when touched with a bare finger. In one case, the cerata were observed to exude a rubber glue-like mucus and twitch for at least half an hour after being dropped, presumably serving to distract or entangle a potential predator. Two other animals of the "greenish centered form" that were handled with probes or spoons didn't autotomize there cerata suggesting that they can discriminate between casual contact and a potential threat. Branches of the digestive gland appear to be concentrated in the lateral cerata that aren't autotomized. Specimens of the pale form (lacking greenish centers in their cerata) seem to be less sensitive, seldom (if ever?) autotomizing their cerata during handling.
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