Amerianna

Amerianna
The shell of Amerianna carinata
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Mollusca
Class: Gastropoda
Superorder: Hygrophila
Family: Planorbidae
Subfamily: Miratestinae
Genus: Amerianna
Strand, 1928
Type species
Physa (Ameria) carinata H. Adams, 1861
Synonyms
  • Ameria H. Adams, 1861; junior homonym
  • Amerianna (Ameriella) Cotton, 1943; junior subjective synonym
  • Ameriella Cotton, 1943; junior subjective synonym
  • Physa (Ameria) H. Adams, 1861; junior homonym

Amerianna is a genus of freshwater snails in the family Planorbidae. These species typically possess shells with large openings and flat backs, and have grey skin. They may be found across a large area of the Southwest Pacific Ocean, most notably Australia.

Taxonomy

The genus Amerianna was first described in 1861 as a subgenus of Physa, as Physa (Ameria). It included 5 species, all of which were newly described. In 1928, it was promoted to a full genus, and was also moved to the family Planorbidae, where it remains today. A 1943 paper named the subgenus Amerianna (Ameriella), but it is no longer considered valid.

The type species is Amerianna carinata.

Description

The flat, angled spire of Amerianna reevii

Shell characteristics

Species in this genus have left-coiling (sinistral) shells, where each shell revolution (whorl) is usually flattened and angular at the posterior of the shell. Typically, a very short or concave spire is present. The shell opening (aperture) is nearly as long as the shell itself. The edge (lip) of the aperture is angled at the back of the animal, and rounded towards the front. The inside edge of the shell (the columella) is slightly folded. Hairs may be present on the outside of the shell in a spiral arrangement, especially in immature individuals.

Sometimes, the back of the shell will be rounded instead of angled, as in the case of Amerianna cumingii.

Other characteristics

The penis is not branched, and possesses a pore on either the tip or the side. The penis sheath is hardly distinguishable from the preputium, and there are no accessory organs. The preputium is folded along its internal wall. The bursa copulatrix (sperm-storing organ) is long and oval-shaped, and is located at the far end of the vagina.

The grey mantle of Amerianna compar

The skin (mantle) of the animal is typically highly pigmented, appearing grey in coloration. The gill (pseudobranch) is highly folded, and joins to the mantle towards the front of the animal.

The radula (toothy tongue-like appendage) has more than 24 teeth per row. The central (rachidian) tooth has two cusps of equal size. Bordering the rachidian tooth on each side are 12 lateral teeth. Each lateral tooth has three cusps, which are of unequal size. At the far edge of the radula lie the marginal teeth, which are similar to the lateral teeth, but with more branching of the cusps. The similarities between the radulae of Amerianna and the genus Planorbis were used as justification for its movement to the family Planorbidae.

Distribution and habitat

Species in this genus are found in fresh water, and though most are native to Australia, at least 3 species may be found on other islands in the Southwest Pacific.

Species

The number of species in the genus is debated, but nonetheless includes:

Synonyms

Subgenus:

Species:

References

  1. 1 2 Strand, Embrik (1928). "Miscellanea nomenclatorica zoologica et palaeontologica I–II". Archiv für Naturgeschichte (in German). 92A (8): 63.
  2. 1 2 3 4 5 6 Vinarski, Maxim (2020). "Amerianna Strand, 1928". WoRMS. World Register of Marine Species. Retrieved 2 June 2026.
  3. 1 2 Adams, H. (1861). "Descriptions of a New Genus and some New Species of Shells from the Collection of Hugh Cuming, Esq". Proceedings of the Zoological Society of London. 29: 144. ISSN 0370-2774. LCCN 86640225. OCLC 1779524.
  4. ↑ Cotton, Bernard C. (1943). "More Australian freshwater shells". Transactions of the Royal Society of South Australia. 67 (1): 143. ISSN 2204-0293. LCCN 95641252. OCLC 6271809.
  5. 1 2 3 4 5 6 7 8 9 Walker, J. C. (1988). "Classification of Australian Buliniform Planorbids (Mollusca: Pulmonata)" (PDF). Records of the Australian Museum. 40 (2): 75–78. Archived from the original (PDF) on 25 May 2024.
  6. ↑ Adams, H. (1861). "Descriptions of a New Genus and some New Species of Shells from the Collection of Hugh Cuming, Esq". Proceedings of the Zoological Society of London. 29: 143–144. ISSN 0370-2774. LCCN 86640225. OCLC 1779524.
  7. ↑ Cotton, Bernard C. (1942). "Some Australian freshwater Gasteropoda". Transactions of the Royal Society of South Australia. 66: 75–76.