Bistolida hirundo is uncommon in the Marshalls. At Kwajalein and Enewetak, it is found primarily on relatively shallow lagoon interisland and pinnacle reefs, where it hides beneath rocks at depths of 3-13m. It is similar in appearance to Bistolida kieneri and B. ursellus, two species that are also uncommon to rare but found primarily on the seaward reefs. All three species vary somewhat across their Indo-Pacific ranges and in some areas are difficult to tell apart, but those in the Marshalls are fairly distinct from one another. Bistolida hirundo when fresh tends to be light to darker bluish gray in color, which fades to a more purplish gray in older specimens. Also, the anterior white transverse band across the dorsum is nearly always shaped like a rough question mark and is often completely surrounded by the dorsal blue gray color. Its teeth are relatively coarse and extend a bit over half way across the base. In both B. kieneri and B. ursellus, the anterior band is irregular in shape and generally crosses completely through the dorsal coloration. The subspecies found in the Marshall Islands is Bistolida hirundo rouxi.
The dorsal bluish gray color fades in older empty shells. 12.3mm, 19 November 1990
14.4mm, 9 September 2002
17.2mm
Updated 1 June 2024