Opisthobranch of the Week Data
I've not personally seen Berghia chaka here in the waters of Okinawa's main island, however Atsushi Ono mentions (pers. comm.) that the above featured animal is one of two collected animals he has found in the Keramas*. Atsushi reports seeing in excess of ten individuals and considers the species to be uncommon there. Atsushi collected the above aeolid from a rock of a shallow reef. I've added a second page with Atsushi's second collected specimen of B. chaka.
On these pages I've previously featured several images (2 Feb '04) of Berghia chaka, kindly furnished by Jun Imamoto, also photographed from the waters of Gahi Island in the Kerama Islands.
Berghia chaka was described by Gosliner (1985) based on specimens from Jesser Point, Sodwana Bay National Park, Natal, southern Africa. The following description of external morphology and coloration are taken from Gosliner (1985):
The living animals reach 10 mm in length. The oral tentacles are slender and tapered. The rhinophores are approximately equal to the oral tentacles in length and possess scattered, elongate papillae. The foot is moderately broad. Anteriorly it is deeply incised and slightly more posteriorly a transverse groove is present. The anterior end of the foot is broad and rounded, without angular or tentacular extensions. The cerata are irregularly shaped with a few tubercles along their lengths. The anterior right digestive branch consists of a single arch of eight cerata. The first branch of the right posterior digestive system is also an arch composed of ten cerata. The two to three branches posterior to this may consist of partial arches or linear rows of two to six cerata. The gonopores are situated ventral to the first ceratal arch while the anus is located within the second arch. The nephroproct is immediately anterior to the second ceratal arch.
The living animals were translucent white covered with a dense pattern of opaque white pigment over much of the body. The head and basal halves of the rhinophores and oral tentacles are covered with chocolate brown pigment. Brown is also present at the bases of the cerata and more diffusely on the dorsal portion of the foot. The digestive gland within the cerata is rusty brown. The cerata are ornamented with opaque white pigment, which is most dense on their anterior side and on the irregular tubercles. The tips of the cerata are opaque white. A thin subapical band of chocolate brown is present, as is a wider band of opaque white.
* Keramas = the Kerama Islands Group, located 30 ~ 40 kilometers west of the Okinawa capitol, Naha.