young, 9 mm
on food sponge
Aldisa sp. #2
|Maximum size: 24 mm.
dorid with red gills frosted in white. There are three crater-like
depressions on the notum. The
rhinophores and gills are flanked by irregular patches of white pigment
and there are usually smaller patches midway
between them. The notum is covered by a network of
tall, sharply delineated ridges with papillae confined to their junctions. The
white pigment is dense and usually crosses the ridges while the bottoms of
the pits between the ridges are reticulated with lighter pigment. It may
be distinguished from Aldisa pikokai by
its sharply delineated ridges, its denser white pigment and the
presence of reticulated pigment in the pits between the ridges. It may
distinguished from Aldisa sp. #1 by the presence
of three crater-like depressions on its mid-notum (in contrast to two
in the latter species).
Aldisa sp. #2 is
a moderately common nocturnal dorid found under rocks at moderately
highly exposed rocky sites. It may occur at depths of 1-24 m (3-80 ft)
but photos confirm a minimum range of 1-8 m (3-26 ft). It apparently
feeds on an orange-red encrusting sponge. (see photos)
Big Island, Maui, Oahu, Niihau and Pearl & Hermes Reef : may also be known from Kwajalein and Moorea. (Note 1)
sp. in Kay, 1979 (on p. 456) is actually of this species, instead. It
listed as Aldisa sp. in
Bertsch and Johnson, 1981 (top photo). It's referred to as the "pitted nudibranch"
in Hoover, 1998 & 2006 (under the name Aldisa pikokai). It's listed on many other sites as Aldisa pikokai
and was probably lumped with that species in the original description. It's also possible that examination of the holotype of A. pikokai
will ultimately result in assigning the name to this form, instead. It may
have been first reported from Hawaii in Kay & Young, 1969 (as Halgerda rubra).
Photo: CP: 24
mm: Kapalua Bay, Maui; April 24, 2008.
Observations and comments:
1: Both Aldisa sp. #2 and Aldisa pikokai
probably represent widespread Indo-Pacific lineages that tend to mimic
other in any particular region. Conceivably, both may be composed of
multiple allopatric species. The populations that occur in Kwajalein and
Moorea appear very similar to the Hawaiian animals but determining
their precise relationships will require further work.