Table 1 A summary of the morphology based species groups, key morphological characters for each group [31], and the phylogenetic support obtained for each group in our analyses

Atlanta brunnea

Atlanta brunnea Gray, 1850

I

Both aragonite

Small shell (< 2 mm) with a tall keel. Larval shell is tall, conical, covered with ornamentation and with a prominent carina slightly above mid-whorl height

Yes

Atlanta turriculata d’Orbigny, 1836

I

Atlanta vanderspoeli Wall-Palmer, Hegmann & Peijnenburg, 2019

I

Atlanta inflata

Atlanta ariejansseni Wall-Palmer, Burridge & Peijnenburg, 2016

I

Both aragonite

Small-medium sized shell (< 4 mm) with a short or tall keel. Larval shell is flattened, or low conical and either smooth, or ornamented with evenly spaced spiral ridges or punctae.

Yes

Atlanta californiensis Seapy & Richter, 1993

I

Atlanta helicinoidea (A and B) Gray, 1850

I

Atlanta inflata Gray, 1850

I

Atlanta selvagensis de Vera & Seapy, 2006

I

Atlanta lesueurii

Atlanta lesueurii Gray, 1850

I

Both aragonite

The larval shell is very small, with only 2.5 whorls.

Yes - species group together but node support is low (37%).

Atlanta oligogyra (A, B and C) Tesch, 1906

I

Atlanta gaudichaudi

Atlanta echinogyra Richter, 1972

I

Both aragonite

Small-medium shell (< 4 mm). Larval shell flattened to conical with varying numbers of spiral lines (only 1 in A. gaudichaudi).

Yes, but node support is moderate (75%).

Atlanta gaudichaudi Gray, 1850

I

Atlanta plana Richter, 1972

I

Atlanta peronii

Atlanta fragilis Richter, 1993

II

Both aragonite

Medium-large sized shell (< 10 mm). Larval shell is flattened or low conical with no ornamentation (except A. frontieri).

No - species do not group together. A. frontieri groups with A. gibbosa group.

Atlanta frontieri Richter, 1993

II

Atlanta peronii (A, B and C) Lesueur, 1817

II

Atlanta rosea (A, B and C) Gray, 1850

II

Atlanta inclinata

Atlanta inclinata Gray, 1850

II

Both aragonite

Large shell (< 6 mm) with a tall keel. Larval shell large, conical and globose, tilted relative to the adult shell. Larval shell covered with small tubercula.

Yes

Atlanta tokiokai van der Spoel & Troost, 1972

II

Atlanta gibbosa

Atlanta gibbosa Souleyet, 1852

II

Both aragonite

Medium shell (< 4 mm) with a tall keel that is very thin and transparent. Larval shell large, conical and globose, tilted relative to the adult shell. Larval shell smooth.

No - species group together with A. frontieri. Low node support (32%).

Atlanta meteori (A and B) Richter, 1972

II

Oxygyrus

Oxygyrus inflatus (A, B and C) Benson, 1835

I

Inner shell aragonite, outer shell and keel of conchiolin.

Large shell (< 14 mm) very rounded, almost spherical and involute with a tall conchiolin keel. Larval shell heavily ornamented with zig-zig spiral lines. The final whorl of the adult shell is partially composed of conchiolin.

Yes

Protatlanta

Protatlanta sculpta Issel, 1911

I

Aragonite shell, conchiolin keel

Small shell (< 2 mm) of aragonite with a tall conchiolin keel. Larval shell is low conical with 2.5–3 whorls.

Yes

Protatlanta souleyeti (Smith, 1888)

I