young, 7 mm
Melibe engeli Risbec, 1937
|Maximum size: 60 mm (an animal that was probably over 100 mm was seen but not measured).
has a transparent body lightly frosted with brown flecks.
Because of its transparency, the brown branches of the digestive gland
and globular gizzards can be seen through the body wall. (see photo of same animal on white).
The cerata are cylindrical and tuberculate with flattened, leaf-like
tips (tubercles may be compound in some animals). The notum is covered with elongate papillae and there are
leaf-like crests on the posterior margins of the rhinophore sheaths.
The tips of the tubercles, cerata and papillae are tinged with blueish
Melibe engeli is a
common species found in Halimeda
kanaloana beds at depths of 5-18 m (16-49 ft). In that
habitat, it is one of the most numerous opisthobranchs, sometimes
occurring in large blooms. (Note 1) In
addition, it is occasionally found in protected to moderately exposed
rocky habitats at depths of as little as 1 m (3 ft). However, it can
swim readily by lateral flexing and most animals found in rocky
habitats were in "catchment" areas down-current of Halimeda beds suggesting that they
may have been carried in from deeper water. (Note 2)
to feed primarily at night when it moves to the tips of the
algae and sweeps the water rhythmically with its hood. (Note 3) During the day, it conceals itself in the
algae rather than under rubble. (Note 4) It lays
a delicate, telescoping coil of white to tan eggs with 3 to 5 whorls
(usually on algae). Hatching may occur in as little as
two days in the laboratory.
Big Island, Maui, Oahu and French Frigate Shoals: widely distributed in the
Taxonomic notes: It was first
in Hawaii from Hekili Point, Maui by CP on Sept. 27,
Black Rock, Maui; Nov. 11, 2003.
Observations and comments:
Note 1: The largest
bloom we've encountered was in the Halimeda
kanaloana beds at Wahikuli, Maui on Oct. 25, 1995. Many
thousands of animals were visible covering the Halimeda and we spent the entire
dive in a cloud of swimming Melibe
engeli disturbed be our passage.
Note 2: Of the few dozen
animals we've seen in rocky habitats, only four were 3 to 11 mm in length. In contrast, animals as small as 3-4 mm are
common in Halimeda kanaloana beds.
That suggests that larval settlement may be largely confined to Halimeda kanaloana (perhaps, with the few small juveniles found in rocky habitats settling on other Halimeda spp.). Also, an aggregation of
about 14 large animals was observed on multiple occasions in a
catchment area at Hekili Point, Maui between Sept 27 and Oct 16, 1993.
When checked after a period of high surf on Oct. 27, only one could be
located. On Nov. 1, there were 12 animals at the site but they
appeared to be smaller than the animals in the previous aggregation
suggesting turnover. On Nov. 9 only one could be found. This supports
the idea that drifting/swimming animals are being deposited and
dispersed by currents and surf.
Note 3: On multiple
occasions in fall, 1993 we observed large animals actively feeding at
night. Despite an extensive search we couldn't find any by day
suggesting that they'd concealed themselves deeply within the algae.
None were found under rubble although a comprehensive search wasn't
Note 4: Its transparent
body with fine brown flecks combined with its habit of feeding at night
while resting in algae (rather than under rubble) during the day
supports the suggestion that M.
engeli may supplement its food with
zooxanthellae in the manner of Melibe
megaceras. (see photos)