Trivirostra edgari (Shaw, 1909)
|Maximum size: 9 mm shell length (Severns, 2011).
In mature animals, the mantle is rust-red blotched with brown and flecked with
white. It's studded with retractile, compound tubercles. The body is
translucent orange and its upper surface is irregularly reticulated with white. Shells are white and
typically larger (and with a higher profile) than in the similar-appearing
The apical margin is usually straight to slightly concave and there is
usually some sign of axial sculpture between the ribs. Size at
maturity is variable (5-9 mm shell length based on my material and Severns, 2011).
Natural history: Trivirostra edgari
is a moderately common species in
moderately exposed to exposed rocky habitats and Halimeda kanaloana beds from 3-30 m (10-98 ft).
Big Island, Maui, Oahu, Kauai and Maro Reef: widely distributed in the Indo-Pacific.
It's listed in Kay, 1979, as Trivia edgari. In addition it may be listed in Severns, 2011 as Trivirostra keehiensis, Trivirostra scabriuscula, Trivirostra pellucidula, and Trivirostra insularum. (Note 1)
CP: found by PF; Kapalua Bay, Maui; April 25, 2015.
Note 1: We have seen many living animals of both T. hordacea and T. edgari
with the characteristics of the living animals being quite consistent.
We have not seen any animals that would suggest the presence
of other species in the genus. Shells are much more ambiguous. Both
species show a wide size range at maturity with some overlap. (see photo)
And, they show substantial variation based on ontogeny and size at
maturity. Therefore, it seems more parsimonious to assign the Hawaiian
material to two variable species rather than to a multitude of more
narrowly defined species as suggested by Severns, 2011. We have
tentatively assigned the illustrations in that source to either T. hordacea or T. edgari
based on their dorsal margins, profiles and axial sculpture. This is
not intended to address the question of whether or not the
material in the original descriptions of those species is distinct.