''Pebasiconcha immanis'' is an extinct

species In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of ...

of air-breathing land snail, a

terrestrial Terrestrial refers to things related to land or the planet Earth. Terrestrial may also refer to: * Terrestrial animal, an animal that lives on land opposed to living in water, or sometimes an animal that lives on or near the ground, as opposed to ...

pulmonate gastropod

mollusk Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is es ...

in the family

Acavidae Acavidae is a taxonomic family of air-breathing land snails, terrestrial pulmonate gastropod molluscs in the superfamily Acavoidea (according to the taxonomy of the Gastropoda by Bouchet & Rocroi, 2005). Anatomy In this family, the numbe ...

. The type locality of ''Pebasiconcha immanis'' is the

Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recent" ...

Pebas Formation The Pebas Formation is a lithostratigraphic unit of Miocene age, found in western Amazonia. The formation extends over , including parts of Brazil, Peru, Ecuador and Colombia.Wesselingh et al., 2006 It is interpreted as representing the deposits ...

in the Colombian and Peruvian Amazonia.Wesselingh F. P. (2006). "Molluscs from the Miocene Pebas Formation of Peruvian and Colombian Amazonia". ''

Scripta Geologica ''Scripta Geologica'' is a peer-reviewed scientific journal that publishes on vertebrate and invertebrate palaeontology, palaeobotany/palynology, stratigraphy, petrology, and mineralogy, including gemmology with a focus on systematics. It is publi ...

'' 133: 19-290. Figure 274
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Discovery and naming

Initially believed to belong to the genus ''

Strophocheilus ''Strophocheilus'' is a genus of gastropods belonging to the family Strophocheilidae Strophocheilidae is a taxonomic family of air-breathing land snails, terrestrial pulmonate gastropod mollusks in the superfamily Acavoidea (according to t ...

'' by Spix (1827), ''Pebasiconcha'' is a common fossil shell from western Amazonia. Fieldwork in the autumn of 1991 recovered several exceptionally large specimens, however working conditions of the time did not allow the safe transport of entire specimens, which were subsequently broken and disintegrated. However researchers did manage to take photographs of the complete specimens in situ. Later expeditions also failed to produce intact specimens, with the second visit in 1996 only recovering further shell fragments. During this visit researchers also discovered another well preserved specimen in a shop in

Iquitos Iquitos (; ) is the capital city of Peru's Maynas Province and Loreto Region. It is the largest metropolis in the Peruvian Amazon, east of the Andes, as well as the ninth-most populous city of Peru. Iquitos is the largest city in the world tha ...

, Peru, which was however not for sale. While unable to purchase the fossil, photos could be taken. Due to this the description of ''Pebasiconcha'' was based on photographs and shell fragments. The generic name is derived from the Pebas Formation where the fossils have been found and the Latin word "concha" meaning shell. The species name immanis, meaning huge or enormous, was chosen to reflect the animals massive size.

Description

The height of the

shell Shell may refer to: Architecture and design * Shell (structure), a thin structure ** Concrete shell, a thin shell of concrete, usually with no interior columns or exterior buttresses ** Thin-shell structure Science Biology * Seashell, a hard o ...

is more than 25 cm (more than 250 mm) making ''Pebasiconcha'' one of the largest known land snails. "''Amazoniconcha immanis''"
accessed 13 September. The shell is ovoid in shape with up to six moderately convex whorls. The body whorl has a markedly constricted aperture and a prominent asymmetrical knob on the upper half of the body whorl.The border of the outer lip is neither reflected nor thickened. One specimen with a particularly large mytoid knob may indicate a specimen which either possessed a shell higher than 30 cm or simply a proportionally larger knob than the holotype specimen.

Paleoenvironment

''Pebasiconcha'' lived in the Pebas Mega-Wetlands that covered large parts of northern South America during the middle Miocene period, an environment known for its rich freshwater mollusc fauna. The Mega-Wetland included swamps, marshes, embayments, rivers and forested riverbanks. The terrestrial areas of the wetlands were inhabited by a minimum of two land snails, ''Pebasiconcha'' and ''

Orthalicus linteus ''Orthalicus'' is a genus of land snails in the family Orthalicidae. MolluscaBase eds. (2021). MolluscaBase. Orthalicus H. Beck, 1837. Accessed through: World Register of Marine Species at: http://marinespecies.org/aphia.php?p=taxdetails&id=995 ...

''. While the later most likely inhabited the tree trunks and branches as its extant relatives, ''Pebasiconcha'' is hypothesized to have lived in the humid bottom layers.

References

Acavidae Miocene gastropods {{Paleo-gastropod-stub