Tylodina sp. #1
|Maximum size: 6.3 mm
(extrapolated from shell length).
a yellow body and a cap-shaped external shell. The
flexible, translucent, periostracum extends well beyond the margin of
calcified portion of the shell and the apparent radial ridges represent
thickened portions of the periostracum. (Note 1)
Tylodina sp. #1
is known from only four live animals found in moderately protected
to moderately exposed rocky habitats at depths of 3-4 m (10-13
ft). However, several thousand shells have been found in sand samples
taken near rocky areas suggesting that it's actually a common species.
It's nocturnal in habit
and appears to be restricted to the undersides of rocks while its periostracum acquires a thin layer of
detritus making it extremely difficult to see in the field. (Note 2) It probably
feeds on sponges.
Maui, French Frigate Shoals, and Midway: possibly known from French
first recorded in Hawaii from Napili Bay, Maui by CP
Sept. 12, 1998.
found by CP: Kapalua Bay, Maui; Oct. 1, 1999.
Observations and comments:
A minority of shells from beach
drift and subtidal sand samples showed strong green florescence under
ultraviolet light (395 nM). There was no obvious correlation of
florescence with shell morphology or wear. Perhaps, the difference is
due to diet (different minerals/proteins incorporated into the shell?).
Note 2: When held in a dish with a lid,
this species consistently crawls upwards onto the underside of the lid,
then settles and clings tenaciously to the surface. That suggests that
it's "programed" behaviorally for an upside-down orientation.