Umbraculum sp. #2
|Maximum size: about 127 mm
large species with a broad, cap-shaped external shell
covering the center of the notum. The mantle is covered with large, conical tubercles and its
color varies from white (in small juveniles) through pale brown to dark brown, usually
with contrasting cream pigment of the tips of the tubercles. Very young animals may
have less well developed tubercles than adults. Shells of shallow water
animals are usually overgrown with algae but remnants of a hairy
periostracum may be present around their margins. Its shell is more
calcified than the shell of Umbraculum sp. #1.
Umbraculum sp. #2
is a moderately rare nocturnal species found in moderately exposed to
rocky habitats. It occurs in tide pools and to depths of at least 162 m
(532 ft). The record depth is based on photographs taken from HURL
submersibles. It feeds on sponges and lays a frilly, cream egg mass
(although the color of the egg mass may turn out to be variable). (Note 1)
Big Island, Maui, Oahu and Midway: perhaps, known from the western Pacific and South Africa? (Note 2)
species is illustrated as Umbraculum sinicum (Gmelin, 1791) in Kay, 1979 and Johnson, 1982 as well as Umbraculum umbraculum
1998 & 2006. It's referred to as the "umbrella shell" by Kay and the "umbrella slug" by Hoover. In both Kay and
Hoover, however, the text implies that it's being lumped with Umbraculum sp. #1 and Umbraculum sp. #3. The illustration of Umbraculum sinicum in Edmondson, 1946 also appears to be of this species. It may have been
first reported from Hawaii in Eydoux & Souleyet, 1852 (as Umbrella indica). The shells labelled U. sinicum in Morris, 1974 and Tinker, 1958 may be this species but their assignment is ambiguous.
Photo: CP: 94
mm, brown; found by student; tide pool, Napili Bay, Maui; Sept. 8, 1995.
Observations and comments:
1: The one egg mass we've seen
associated with this species was white but related West Pacific animals
have been photographed laying (or in
association with) egg masses ranging from white to peach to yellow, perhaps reflecting differences in diet.
Note 2: This species appears to be closest to populations of Umbraculum from the Western Pacific and South Africa.
The Western Pacific population has a variable background color with tubercles that lack
cream tips but have darker pigment around their bases. In structure,
its tubercles are closer to those of the sympatric population of Umbraculum sp. #3 making it more difficult to separate the two (without reference to color) than in Hawaii. It's possible that Umbraculum
sp. #2 will ultimately fall within the range of variation of the
Western Pacific population. However, its
smaller tubercles, lack of variation in background color and the
presence of cream tips on its tubercles suggest that it's had a substantial period of
isolation and support the possibility that it's a regional endemic. The South African population may or may not represent a third species in the lineage.