Melibe megaceras Gosliner, 1987
|Maximum size: about 76 mm.
species has a nearly transparent body decorated with brown flecks and cream patches. The cerata are smooth to weakly papillate and slender with long,
extending from their tips. The branch tips range from transparent to red-brown or blue. (Note 1) The notum and oral hood have scattered elongate
papillae and the rhinophores are slender.
Melibe megaceras was rarely seen on
Maui until 2020 when many animals and their egg masses were seen in Halimeda kanaloana patches at a depth of 7-8 m (24-27 ft). Gosliner (1987) reports that it may be seasonally abundant on shallow
sand flats on Oahu where it typically rests with the cerata spread flat
against the sand. It may derive much of its nutrition
zooxanthellae (Symbiodinium microadriaticum) that it retains in its tissues. (Kempf, 1984) (Note 2) Like most Melibe spp, it can swim by lateral flexing, if disturbed. It lays a small, tightly-coiled, cream egg mass. (Note 3)
Maui and Oahu: widely distributed in the Indo-Pacific.
was first recorded in Hawaii from Kaneohe Bay, Oahu by Terry
Gosliner on July 3, 1981.
Photo: Daniel Jennings-Kam: 52 mm: found in HIMB sea tanks, Coconut Island, Oahu; July 18, 2012.
Observations and comments:
1: Presumably, differences in
transparency are due to variation in the density of zooxanthellae in its
tissues. However, variation in the color of the branch tips might
reflect retention of different pigments from the animals it eats.
Note 2: The typical posture of these animals while resting on sand may have evolved to maximize exposure of the zooxanthellae to light. However, to a human eye, resting animals look much like the swimming anemone, Boloceroides mcmurrichi, (a species that is also common in the same habitat) with the long, branched cerata resembling its tentacles. Mesacmae
sp. and at least one other unidentified, sand-dwelling anemone are also
similar in appearance. So, perhaps, the form of the cerata evolved as mimicry?
Note 3: The egg masses laid in the HIMB
sea tanks differ somewhat in form from those found associated with
animals in the field by Kelly Mccaffrey and others in 2020. The latter
appear thicker, contain larger eggs and have a long anchoring filament
extending into the sand. This may be due to differences in development
stage and substrate. However, there's some chance that the species lays
both planktotrophic and lecithotrophic eggs depending on circumstance,
that the animals lumped under this name include two cryptic species or
that the egg masses were actually laid by something else in the field.