The 'Heteropoda', in modern systematics indicated as 'Superfamily Pterotracheoidea' [belonging to the Order Sorbeoconcha, Superorder Caenogastropoda, Subclass Orthogastropoda; compare Beesly, Ross & Wells, 1998: 607] comprise three families, viz. the Atlantidae, the Carinariidae and the Pterotracheidae, the species of which all have a holoplanktonic way of life. Heteropod shells are all dextral.
In the Atlantidae some 20-21 species are known from the Recent fauna, belonging to three genera. In Oxygyrus only the early part of the shell is calcified, whereas the younger parts are cartilaginous. The extant species O. inflatus (better known with the incorrect name O. keraudreni) is also known as a fossil from the Pliocene and younger. Its tiny shell is completely involute (see illustration below).
Of the genus Protatlanta only the type species, P. souleyeti (Smith, 1888) is still living. Various other species, some of these still undescribed, are known from the Miocene onwards.
The numerous Recent species of Atlanta are difficult to identify because of their very small and similar shells, and as some of the differences between the species were described on the soft parts (eyes, radula, operculum). See the many papers on this subject by e.g. Richter, and Seapy, and van der Spoel's (1976) book.. Fossil representatives of Atlanta are known for example from the Caribbean and the Mediterranean. Here, the identification is even more difficult, because of insufficient preservation to observe the protoconch micro-ornament. One of those marvellous colour pictures of Lalli & Gilmer, showing the living Atlanta animal with crystal-clear shell, is reproduced here, together with some examples of fossil species.
Many interesting details of this superfamily can be found in Roger Seapy's contributions to the Tree of Life website: http://tolweb.org/Atlanta/28752/2009.03.16
Oxygyrus inflatus Benson, 1835
Bowden, Jamaica (Pliocene). National Museum of
Natural History (Leiden, The Netherlands), reg. RGM 396.006
Published in Janssen (1998, pl. 1, fig. 3a-b); bar length = 1 mm\
Protatlanta rotundata (Gabb, 1873)
Dominican Republic, Río Gurabo, at mouth of Arroyo Bajón, Sta. 15903 (Late Miocene, Cercado Formation, Globorotalia humerosa Zone).
Naturhistorisches Museum (Basel, Switzerland), reg. NMB H 17618; published in Janssen (1999, pl. 2, fig, 4a-c), apical, frontal and umbilical view respectively; bar length = 1 mm
Atlanta peroni Lesueur, 1817
Living specimen, c. x 7.5. Reproduced from Lalli & Gilmer, 1989 (color fig. 2)
Atlanta diamesa Woodring, 1928, holotype
Bowden, Jamaica (Pliocene). United States national Museum (Smithsonian Institution), reg. USNM 369335. Published in Janssen (1998, pl. 1, fig. 1a-c); bar length = 1 mm
Miocene (Langhian), Upper Globigerina Limestone Formation, of Mdina (Malta), phosphatic internal mould. RGM collection (unregistered)
bar length is 1/10 mm
Carinariidae are beautiful animals with a reduced shell in which the soft parts do not fit. In life position the transparant shell is seen below the animal. Apart from the genus Carinaria (with 9 recent species) and the fossil genus Striocarinaria the genera Pterosoma and Cardiapoda are recognised. The latter two up to now are only known from the extant fauna. The shell of Pterosoma still is unknown to me, Cardiapoda has a very small shell with an enormous apertural flange.
Carinaria lamarcki de Blainville, 1817
Living specimen, c. actual size. Reproduced from Lalli & Gilmer, 1989 (color fig. 3)
Striocarinaria striata di Geronimo, 1973, holotype
Vetto d'Enza, near bridge on Torrente Enza (Miocene, Langhian, Bismantova Formation, Vetto Member). Coll. Istituta di Paleontologia dell'Università (Catania, Italy), not registered (leg. L.M.J.U. van Straaten, 1972). Published Di Geronimo (1973, pl. 1, fig. 4)
Cardiapoda placenta (Lesson, 1830)
Atlantic Ocean, 30° N, 60° W, magnification not indicated. Reproduced from van der Spoel (1976, p. 398, fig. 160a-b)
The Pterotracheidae family includes two genera, Pterotrachea and Firoloida. Adult Pterotrachea species have no shell and thus are exclusively known from the recent fauna. The monotypic genus Firoloida, with type species F. demarestia Lesueur, 1817 is found in tropical and subtropical areas of all oceans. Firoloida also is not yet known as a fossil. The protoconch of this species is beautifully granulated.
Firoloida demarestia Lesueur, 1817
Manihiki Plateau Expedition, Pacific Ocean, sta. 344 (recent). National Museum of Natural History (Leiden, The Netherlands), not yet registered
bar lengths = 0.1 mm (upper) and 0,01 mm (lower)
I thank Roger Seapy (in litt., 2001) for some data concerning systematics.