young, 1.4 mm
Julia exquisita (Gould, 1862)
|Maximum size: 7.2 mm
(extrapolated from shell length).
to greenish-brown shell marked by radiating
rows of green or brown spots that increase in number with age. The
larger spots are associated with "comet tails" of cloudy white. The
hinge tooth is proportionately larger and more oval than in Julia zebra
but smaller than in Julia sp. #2. The animals are
green, sometimes frosted with brown, and flecked with white. There are
usually irregular white patches between the eye spots and at the
midpoint of each rhinophore. Several broad bands of white show
through the weekly translucent shell along the hinge line. Rarely, the
green or brown spots on the shell may be lacking. (Note 1)
Julia exquisita is
a common (though rarely seen) diurnal species found in moderately
protected to exposed rocky habitats. It occurs at depths of < 1 to 5
m (< 3 to 16 ft). Bright green animals predominate at the shallower
end of the range while brownish animals predominate at the deeper end. (Note 2) According to Kawaguti and Yamasu (1966),
it feeds on Caulerpa ambigua
and spawns on Microdictyon
(as Julia japonica). (Note 3)
Alison Kay also found it in association with Microdictyon on Kauai in 1962. (Kay, 1962c) It lays an irregularly cylindrical orange
egg mass that hatches
in about eight days in the laboratory.
Big Island, Maui, Oahu, Kauai, French Frigate Shoals, Laysan and Midway: widely
distributed in the
Kuroda & Habe, 1951 may
be a synonym of this species. Live animals were first recorded in
Hawaii from Koloa, Kauai by
Allison Kay on Feb. 2, 1962. (Kay, 1962b) The first shell material was
reported in Gould, 1862. In southern Japan, the number of rows of
radiating spots appears to be much more variable than in Hawaii.
However, the absence of a "butterfly-shaped" marking on the hinge in
live animals and the larger hinge size in shells still appear to
distinguish those animals from J.
green; 4.8 mm: Hekili Point, Maui; March 23, 2007.
Observations and comments:
1: Shells of this species show
moderately strong red fluorescence under ultraviolet light (395 nM),
most prominently when worn.
Note 2: There's some possibility that
the bright green and brown forms might be different species. However, a
bright green and a brown animal held together spawned and produced
fertile eggs after 14 days in isolation. Although some sacoglossids may
retain sperm for such periods, this observation provides some support
for lumping them. In addition, some animals might be
interpreted as intergrades
and the underlying pattern of white pigment, as well as shell
are identical in the two forms. Perhaps, the association of different
colors with specific depths reflects a difference in diet?
Note 3: Although it's found widely in habitats with mixed algal
turf, we haven't found this species in association with any particular
species of Caulerpa in
Hawaii. Also, the various species of Caulerpa
seem too patchy in distribution for any single one (or combination?) to account for the
distribution of Julia exquisita. Perhaps,
a somewhat broader diet?