The Bellerophontida is a

taxonomic Taxonomy is the practice and science of categorization or classification. A taxonomy (or taxonomical classification) is a scheme of classification, especially a hierarchical classification, in which things are organized into groups or types. ...

order of extinct marine mollusks that are found in the

fossil record A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in ...

from the

Lower Cambrian The Cambrian Period ( ; sometimes symbolized Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million years ago (m ...

to the

Lower Triassic The Early Triassic is the first of three epochs of the Triassic Period of the geologic timescale. It spans the time between Ma and Ma (million years ago). Rocks from this epoch are collectively known as the Lower Triassic Series, which is a un ...

. They are considered by some experts to be primitive

sea snail Sea snail is a common name for slow-moving marine gastropod molluscs, usually with visible external shells, such as whelk or abalone. They share the taxonomic class Gastropoda with slugs, which are distinguished from snails primarily by the ...

s with primarily symmetrically coiled shells,

marine Marine is an adjective meaning of or pertaining to the sea or ocean. Marine or marines may refer to: Ocean * Maritime (disambiguation) * Marine art * Marine biology * Marine debris * Marine habitats * Marine life * Marine pollution Military * ...

gastropod The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. T ...

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 e ...

s. R.C Moore and J. Brooks Knight ''et al'' 1960 Treatise on Invertebrate Paleontology, Part I Mollusca 1 recognized bellerophonts as true gastropods, placing them as the suborder Bellerophontina in the subclass

Prosobranchia Prosobranchia was a large taxonomic subclass of sea snails, land snails and freshwater snails. This taxon of gastropods dates back to the 1920s. It has however been proven to be polyphyletic (consisting of more than one lineage of descent). Gene ...

, order

Archaeogastropoda Archaeogastropoda (also known as Aspidobranchia) was a taxonomic order of sea snails used in older classifications of gastropods, i.e. snails and slugs. Archeogastropoda are marine prosobranch gastropod mollusks, mainly herbivores, typically havi ...

. Some more recent workers in the field have expressed uncertainty as to the taxonomic placement of this group.

Shell morphology

Shells of bellerophontids are most commonly isotrophic (coiled symmetrically), rarely slightly asymmetric. Most are closely coiled with some general more openly coiled, cyrtiform; predominantly with a median slit in the upper lip of the aperture, or with a series of openings known as tremata, usually generating a

selenizone A selenizone (from the Greek "selene" meaning "moon", and "zone" meaning "girdle") is an anatomical structure that exists in the shells of some families of living sea snails: the slit shells, the little slit shells and the abalones, which are m ...

which was probably exhalant in function. The shell wall is of variable thickness and no evidence of

nacre Nacre ( , ), also known as mother of pearl, is an organicinorganic composite material produced by some molluscs as an inner shell layer; it is also the material of which pearls are composed. It is strong, resilient, and iridescent. Nacre is f ...

or of an operculum has been found. Nothing is known of soft part anatomy of the group, although a simple pair of retractor muscles is inferred from muscle scars. Isotrophic symmetry also suggests paired and equal

nephridia The nephridium (plural ''nephridia'') is an invertebrate organ, found in pairs and performing a function similar to the vertebrate kidneys (which originated from the chordate nephridia). Nephridia remove metabolic wastes from an animal's body. Neph ...

and ctenidia (kidneys and gills).

Taxonomy

According to Knight, ''et al'', the Bellerophontina, as then regarded, includes two superfamilies, the

Helcionellacea The Helcionellacea is one of two taxonomic superfamilies of extinct primitive marine molluscs within the order Bellerophontida. This superfamily is thought to be the more primitive of the two superfamilies, the other being the Bellerophontacea. ...

, and the Bellerphonitacea. The

are the more primitive, with more cap-like shells, that are limited to the Cambrian Period. Two small families, the

Helcionellidae Helcionellid or Helcionelliformes is an order of small fossil shells that are universally interpreted as molluscs, though no sources spell out why this taxonomic interpretation is preferred. These animals are first found about in the late Ne ...

and

Coreospiridae Coreospiridae is an extinct family of Paleozoic molluscs of uncertain position taxonomically. They might be snails ( Gastropoda), Helcionelloida, or they might be Monoplacophora. 2005 taxonomy The taxonomy of the Gastropoda by Bouchet & R ...

are included. The Bellerophontacea, which range from the Upper Cambrian to the Lower Triassic, are more developed and more diverse; that taxon contains three families, the

Cyrtolitidae Cyrtolitidae is an extinct family of monoplacophorans in the order Cyrtonellida. Genera * '' Cloudia'' * '' Cyclocyrtonella'' * '' Cyrtolites'' * '' Cyrtonellopsis'' * '' Kolihadiscus'' * '' Neocyrtolites'' * '' Paracyrtolites'' * '' Quasisin ...

Sinuitidae Sinuitidae is an extinct family of Paleozoic molluscs of uncertain position (they were either Gastropoda or Monoplacophora). They had isostrophically coiled shells. Taxonomy The taxonomy of the Gastropoda by Bouchet & Rocroi, 2005Bouchet P. & ...

, and

Bellerophontidae The Bellerophontidae are an extinct family of specialized globose bellerophontids, Paleozoic and early Triassic mollusks of the class Gastropoda. Geological range These mollusks appeared in the Late Cambrian and continued until the Early Triassi ...

, along with subfamilies and tribes. Ponder & Lindberg (1997) included the Bellerophontida, as the Bellerophontinaka, in with the Mimophserina, in the Class Gastropoda, ''incertæ sedis'', excluding them from the

Eogastropoda Eogastropoda was a previously used taxonomic category of snails or gastropods, a subclass which was erected by Ponder and Lindberg in 1997. It was one of two great divisions (subclasses) of the class Gastropoda, the snails. The other subclass of ...

, or

. Bouchet & Rocroi (2005) expressed greater uncertainty, placing the bellerophonts, as

Bellerophontoidea Bellerophontoidea, common name "bellerophonts",Bouchet P. & Rocroi J.-P. (Ed.); Frýda J., Hausdorf B., Ponder W., Valdes A. & Warén A. 2005. ''Classification and nomenclator of gastropod families''. Malacologia: International Journal of Malaco ...

in Paleozoic molluscs with isostrophically coiled shells of uncertain position (Gastropoda or Monoplacophora). More recently, J.P. Wager, 2011P. J. Wagner. 2011. Paleozoic Gastropod, Rostroconch, Helcionelloid and Tergomyan Databas

/ref> included the Bellerophontida as an order in the Gastropoda.

References

{{Taxonbar, from=Q606885 Prehistoric gastropods Prehistoric mollusc orders Early Triassic extinctions Cambrian first appearances