Contributions to Zoology, 85 (4) – 2016Deborah Wall-Palmer; Alice K. Burridge; Katja T.C.A. Peijnenburg; Arie Janssen; Erica Goetze; Richard Kirby; Malcolm B. Hart; Christopher W. Smart: Evidence for the validity of Protatlanta sculpta (Gastropoda: Pterotracheoidea)
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Systematic descriptions

Superfamily Pterotracheoidea Rafinesque, 1814 

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Family Atlantidae Rang, 1829

Genus Protatlanta Tesch, 1908

Type species. Protatlanta souleyeti (Smith, 1888). Originally named Atlanta lamanoni Gray, 1850 and subsequently renamed Atlanta souleyeti by E.A. Smith.

Diagnosis. Genus of Atlantidae with an aragonite shell and a conchiolin keel. The aperture is rounded and sub-triangular in shape without a slit in the shell periphery (as in Atlanta) where the keel ends.

Description. The shell is dextrally coiled and flattened, lenticular in shape, consisting of up to 4 ¼ whorls with a total shell diameter of up to 2 mm. The spire (central, juvenile part of the shell) is slightly elevated, with incised sutures and consists of 2 ½ to 3 ¼ whorls. The final adult whorl inflates rapidly and gives the shell an oval shape when viewed from the apical side. The shell is calcareous with a tall, extremely transparent and strongly truncated conchiolin keel.

Remarks. The keel of Protatlanta is extremely transparent and is often difficult to see in wet specimens. The keel in lost is fossil material, even in relatively recent sediments.

Protatlanta souleyeti (Smith, 1888)

(Fig. 5a-b, e-g, i-j)

Material examined. See supplementary Table S1.

Diagnosis. Protatlanta species with no shell ornamentation.

Description. The spire typically consists of 2 ½ to 3 whorls with a diameter of less than 450 μm. The spire has a smooth surface with no ornamentation. The shell is colourless, however the spire may vary in colour from white to dark brown due to the colour of the soft tissues (Fig. 3e-g). The complete adult shell consists of 3 ½ to 3 ¾ whorls. Eyes are type a and operculum is type a (Seapy, 2011).

Remarks. Juvenile specimens are particularly difficult to identify as their lack of ornamentation and distinctive features can cause confusion with juveniles of Atlanta peronii and Atlanta lesueurii. However, the aperture of juvenile P. souleyeti is more rounded than species in the genus Atlanta.

Distribution. Distribution in the Atlantic Ocean is mainly restricted to northern and southern oligotrophic subtropical gyre regions and equatorial waters. Specimens also found in the Pacific and Indian oceans. The overall latitudinal range is between 47°N to 40°S.

Protatlanta sculpta Issel, 1911

(Fig. 3c-d, h, k-l)

Material examined. See supplementary Table S1.

Diagnosis. Protatlanta species with shell ornamentation on the spire consisting of three irregular spiral lines.

Description. The spire typically consists of 3 to 3 ¼ whorls with a diameter of less than 450 μm. The spire surface is ornamented with three spiral lines, 2 on the spire and 1 along the edge of the shell, in line with the aperture. The spiral lines are present on the second and third whorls and may be partially irregular and interrupted. Scanning electron microscopy (SEM) reveals additional finer ornamentation, including lines of pores on the first whorl and numerous fine spiral lines in the third whorl. The final, adult whorl does not have any ornamentation. The spire shell and sutures has a brown colouration, even in fossil specimens. The final adult shell consists of 3 ¾ to 4 ¼ whorls. Eyes are type a and operculum is type a (Seapy, 2011).

Remarks. Ornamentation is similar to Atlanta gaudichaudi in the first whorls (Newman, 1990) and may cause confusion with juveniles. Atlanta plana also has similar ornamentation, however, the spire of P. sculpta is lower than that of A. plana and A gaudichaudi. Juveniles of P. sculpta have a light brown colouration.

Distribution. P. sculpta is found throughout the Atlantic Ocean from latitudes 41°N to 34°S, but rarely within the northern and southern oligotrophic subtropical gyre regions. Only a single specimen was found outside of the Atlantic Ocean close to the Marquesas Islands in the south Pacific.