Introduction

Atlanta echinogyra is a small species (to 2.5 mm shell diameter). The shell is colorless, although the tissues underlying the shell spire give it a red-violet to red-brown color. The spire is low conical and consists of 3-3/4 whorls. The spire whorls have incised sutures and bear low spiral ridges on the second through most of the fourth whorls. The outer edge of the third and fourth whorls have a raised ridge (seen best in the larval shell). The keel is moderately elevated with a slightly truncate leading edge. The keel does not insert between the last two shell whorls. The keel base is either clear or brown. Eyes type a. Operculum type c, with a gyre that bears a raised spiral row of strong, distally-tapering spines (hence the specific epithet, "echinogyra"). Radula type I, with unlimited numbers of tooth rows and lacking sexual dimorphism. Geographic distribution Indo-Pacific. Vertical distribution limited to the upper 100 m in Hawaiian waters.

Diagnosis

• Shell small, with a maximal diameter of 2.5 mm elevated spiral row of outwardly-directed spines that taper distally
• Shell colorless
• Spire region of shell red-violet to red-brown due to underlying tissues
  
• Spire of 3-3/4 whorls, with low conical shape and deep sutures
• Low spiral ridges present on the second through most of the fourth spire whorls
• Outer edge of third and fourth whorls with a raised ridge
  
• Keel moderately elevated, with a slightly truncate leading edge
  
• Keel does not insert between last two whorls
• Keel base clear (North Pacific Ocean) or dark to yellow-brown (northern Indian Ocean)
  
• Eyes type a
  
• Operculum type c; gyre bears a raised spiral row of distally-tapering spines
  
• Radula type I