Two Rare Costellarids

by Richard Salisbury

Costellaria mica Reeve, 1845 and Costellaria verecundulum Hervier, 1898. It's doubtful you'll ever have to worry about seperating these two shells. That is unless you like hunting for shells with a magnifying glass. Both are small 6 to 15mm. These tiny Costellarids (along with a half dozen other species) live in find silt beneath the rubble in Apra Harbor, Guam. There are many minute shells in this habitat. Most of these shells are covered with a find algae growth, which make them look even more like the silt they live in.

These two shells can be extremely difficult to seperate, especially the juveniles. Costellaria mica is the larger shell reaching about 3/8 inch. It is usually light green in color, sometimes tinged with brown or orange. A fairly wide white central band circles the body whorl. Rows of pustuals form the encircling ribs. This characteristic distinguishes this species from most other Costellarids. Costellaria verecundulum has basically the same color and pattern, except it is circled by many orange lines, which bisect the ribs, forming orange spots on each rib. The ribs are smooth and unbroken, except for a subsutural groove. It is a rather smooth shell, growing to only about half the size of mice. Both are rare, not because of their abundance, but because they are seldom collected. C. verecundulum, until found in Apra Harbor, has been effectively lost since it was described in 1898.