nflata. The shell is oriented with the embryonic shell directed upward; the whorls are then counted based on an imaginary line directed upward from the center of the embryonic shell. The numbers in the sketch denote the end of one whorl and the beginning of the next one. The arrow indicates the number of whorls (4-1/2) comprising the spire. © 2009 Roger R. Seapy
Click on an image to view larger version & data in a new window
Click on an image to view larger version & data in a new windowFigure. Sketches of the whorl sutures on the shell spire and extending onto the first adult shell whorl in Atlanta lesueurii (left) and A. peronii (right). The dashed line in each sketch denotes the ending and beginning point for each spire whorl. The arrow at the bottom of each sketch indicates the number of whorls comprising the shell spire. © 2009
- The shape of the spire is highly variable among Atlanta species and can often serve as a distinctive character (see below). Examples include the tall, turreted spire of A. turriculata, the conical spire of A. brunnea, and the tilted (or "inclined") spires in the A. inclinata and A. gibbosa species groups.
- In addition to spire shape, spire ornamentation can also be very distinctive; ranging from smooth (e.g., the A. lesueurii species group and three of the members of the A. peronii species group) to ornamented by low, elevated spiral ridges (e.g., A. inflata, A. helicinoidea, and A. plana), to highly ornate and elevated sculpture (e.g., A. brunnea, A. echinogyra and A. turriculata).
- Nineteen species are currently regarded as valid in the genus Atlanta. These species are partitioned into seven species groups (see table below). Tesch (1908) was the first to group together the species of Atlanta sharing similar morphologies. He recognized four species groups; the A. peronii-, A. inflata-, A. turriculata-, and A. inclinata-groups. In addition to these, three additional ones are currently recognized; the A. lesueurii-, A. gaudichaudi- and A. gibbosa groups. Except for Tesch's (1908) A. turriculata-group, the composition of Tesch's species groups has changed by species invalidations, the addition of new species over time, and addition of three new species groups. The main changes in Tesch's species groups have occurred in the A. peronii-group (with A. gaudichaudi and A. lesueurii now forming their own species groups) and the A. inclinata-group (with A. gibbosa now forming its own group).
The geographic distribution of the species in the genus are summarized in the last three columns of the table below. The highest number of species occurs in the Pacific (17), followed by the Indian (16) and the Atlantic (12) Oceans. Ten species are cosmopolitan, recorded from all three major oceans, five (A. turriculata, A. frontieri, A. plana, A. echinogyra, and A.gibbosa) are Indo-Pacific, two (Atlanta inflata and A. californiensis) occur only in the Pacific, one (A. selvagensis) is Indo-Atlantic, and one (A. fragilis) has only been recorded from the Atlantic; no species are unique to the Indian Ocean. It should be noted that one species, A. meteori was previously regarded as Indo-Pacific, but was recorded from the northeastern Atlantic by de Vera, Seapy and Hernandez (2006) and must now be regarded as cosmopolitan.
The seven species groups, their contained species, the distinguishing features of each group and species, and each species' geographic distribution are presented in the table below. The species comprising each species group share the same radular type, usually the same opercular type, and, in many cases, the same eye type. Note that the Group Characteristics are not repeated under the Species Characteristics where they are shared by the members of that Species Group.
|Species Group||Group Characteristics||Species*||Species Characteristics||Maximal Shell Diameter (mm)||Number of Spire Whorls||Eye Type||Opercular Type||Radular Type||Atlantic Ocean ||Pacific Ocean ||Indian Ocean |
|A. brunnea- |
|Shell small; keel tall with rounded leading edge; spire tall conical or turreted, sculpted with complex 