young, about 20 mm
Umbraculum sp. #1
|Maximum size: 65 mm.
This is a moderately large species with a broad, cap-shaped external shell
covering the center of the notum. The mantle has small, relatively
simple tubercles and its
color is uniform bright yellow. Shells of
animals are usually overgrown with algae and remnants of a hairy
periostracum may be present around their margins. They are less heavily
than the shells of Umbraculum sp. #2 and Umbraculum sp. #3. (Note 1)
Umbraculum sp. #1
is a rare nocturnal species. Five of the six live animals recorded were
found in tide pools at moderately exposed sites. The sixth was found at
about 4 m (13 ft) in a similar habitat. It probably
feeds on sponges and lays a large, frilly egg mass similar to
of other Umbraculum spp. (Note 2)
Big Island, Maui, Molokai and Oahu: widely distributed in the Indo-Pacific. (Note 3)
This species is lumped with Umbraculum sp. #2 and Umbraculum sp. #3 as Umbraculum sinicum (Gmelin, 1791) in Kay, 1979 and as Umbraculum umbraculum
in Hoover, 1998 & 2006. It's referred to as the "umbrella shell" by
Kay and the "umbrella slug" by Hoover in that context.
However, it seems likely that it's a distinct species
based on its smaller, simpler tubercles; less heavily calcified shell
and uniform yellow color. All three characters appear to be consistently
associated with each other in photos from throughout the Indo-Pacific.
Based on shell calcification and tubercle form, it's probably more
related to the Umbraculum
population found in the Eastern Pacific (also likely distinct) than to
the other Indo-Pacific and Atlantic forms. (Note 4) Pilsbry, 1917 states that "Umbraculum sinicum aurantiacum (Pse.) which Mr. Thaanum has taken at Hilo, appears to be sufficiently distinct from U. sinicum by characters of the shell to warrant a subspecific name." The name suggests that it might refer to this species but Umbraculum sp. #3 is also a possibility. The shells labelled U. sinicum in Morris, 1974 and Tinker, 1958 may be this species but their assignment is ambiguous.
Photo: CP: 65
mm: tide pool; Napili Bay, Maui; Dec. 12, 2004.
Observations and comments:
1: The shell illustrated here (see photo)
showed moderately strong red fluorescence under ultraviolet light (395
nM), mostly on its interior surface. Some juvenile shells identifiable
only to "Umbraculum sp." also showed a hint of red fluorescence.
Note 2: It's been photographed elsewhere in the Indo-Pacific laying a yellow egg mass.
Note 3: There is little variation in color or tubercles throughout its range from Hawaii to Reunion.
The Eastern Pacific population has a uniform background color in any
particular animal and a lightly calcified shell. However, its background
color is variable and its tubercles are tentacular (particularly in
young animals). The Atlantic population has very large, cauliflower-like
tubercles and a moderately calcified shell.