The pyram family is distributed worldwide with more than 6,000 named species in more than 350 nominal genera and subgenera.[2]
This family of micromolluscs has been little studied and the phylogenetic relationships within the family are not well worked out. There is an absence of a general consensus regarding which species belong to a specific genus or subgenus, contributing to much confusion. Schander (1999) names more than 300 supraspecific names.[3] As there has been no serious generic revision of the genera worldwide, generic polyphyly can be expected to be rampant throughout the family. However, the family itself is deemed monophyletic.[4] However a study in 2011 seems to indicate that this family is deeply nested within the Pulmonata instead of the Heterobranchia.[5]
The family is currently divided into 11 subfamilies (Ponder & Lindberg 1997).[6] An alternative interpretation is that the family Pyramidellidae is but one of six families within the superfamily Pyramidelloidea (Schander, van Aartsen & Corgan 1999).[7] Many species are rare or infrequently recorded.
Subfamilies
Subfamilies included within the family Pyramidellidae vary according to the taxonomy consulted. The currently leading taxonomy is the taxonomy of Bouchet & Rocroi (2005).
In 2010 the family Pyramidellidae has been recognized as monophyletic[9][10]
In 2017 the genera Helodiamea Peñas & Rolán, 2017 of deep-water Pyramidelloidea from the Central and South Pacific, and the Perheida Peñas & Rolán, 2017 were recognized.[11]
Problematic taxa
The following genera are currently difficult to place within existing subtaxa of the Pyramidellidae.
Partulida Schaufuss, 1869: synonym of Chrysallida Carpenter, 1856
Planipyrgiscus [sic]: synonym of Planpyrgiscus Laws, 1937
Plotia Röding, 1798: synonym of Pyramidella Lamarck, 1799
Ptychostomon Locard, 1886: synonym of Odostomia Fleming, 1813
Pyrgulina A. Adams, 1864: synonym of Chrysallida Carpenter, 1856
Raoulostraca Oliver, 1915: synonym of Eulimella Forbes & M'Andrew, 1846
Tragula Monterosato, 1884: synonym of Chrysallida Carpenter, 1856
Tropeas [sic]: synonym of Tropaeas Dall & Bartsch, 1904
Distribution
This family is found worldwide, but many species are only found in relatively small geographical ranges. The species found at the Cape Verdes are mainly endemic species.
[13]
Shell description
The length of the slender, elongated (turreted or conical) shells varies between 0.5 mm and 3.5 cm, but most species in the family have shells which are smaller than 13 mm.
The texture of these shells is smooth or sculptured in various forms such as ribs and spirals. Their color is mostly white, cream or yellowish, sometimes with red or brown lines.
The shell of these snails has a blunt, heterostrophic (i.e. whorls appear to be coiled in the opposite direction to those of the teleoconch) protoconch, which is often pointed sideways or wrapped up. The teleoconch is dextrally coiled, but the larval shells are sinistral. This results in a sinistrally coiled protoconch.
The operculum is ovoid and paucispiral, with the apex anterior, a thread-like arcuate ridge on the proximal side, the inner margin notched in harmony with the plaits of the pillar when prominent.
The species are characterized by the lack of jaw or radula, because they are ectoparasites (mostly on polychaetes or other molluscs).
They do not have a radula. Instead their long proboscis is used to pierce the skin of its prey and suck up its fluids and soft tissues. The eyes on the grooved tentacles are situated toward the base of the tentacles. These tentacles have a concave surface. Between the head and the propodium (the foremost division of the foot), a lobed process called the mentum (= thin projection) is visible. This mentum is slightly indented in midline.
The name of this taxonomic family comes from the shape of the shell, which is like a pyramid.[19] More specifically, the shape is like a right circular cone,[20] which is equivalent to a right pyramid whose base has many sides.[21]
References
^Gray, J. E. (1840). Synopsis of the contents of the British Museum, 42nd edition. London. p. 370 pp.
^Schander, Christoffer; Halanych, Kenneth M.; Dahlgren, Thomas; Sundberg, Per (2003). "Test of the monophyly of Odostomiinae and Turbonilliinae (Gastropoda, Heterobranchia, Pyramidellidae) based on 16S mtDNA sequences". Zoologica Scripta. 32 (3): 243–254. doi:10.1046/j.1463-6409.2003.00112.x. S2CID84249963.
^ abSchander, Christoffer; Hori, Shigeo; Lundberg, Joakim (2011). "Anatomy, phylogeny and biology of Odostomella and Herviera, with the description of a new species of Odostomella (Mollusca, Heterostropha, Pyramidellidae)". Ophelia. 51 (1): 39–76. doi:10.1080/00785326.1999.10409399.
^Dinapoli A, Zinssmeister C, Klussman-Kolb A. 2011. New insights into the phylogeny of the Pyramidellidae (Gastropoda). Journal of Molluscan Studies 77:1-7.
^Peñas A. & Rolán E. (2017). Deep water Pyramidelloidea from the central and South Pacific. The tribe Chrysallidini. ECIMAT (Estación de Ciencias Mariñas de Toralla), Universidade de Vigo. 412 pp.
^Høisæter, T. (1965). "Spermatophores in Chrysallida obtusa (Brown) (Opisthobranchia, Pyramidellidae)". Sarsia. 18: 63–68. doi:10.1080/00364827.1965.10409548.
^Robertson, R. (1967). "The life history of Odostomia bisuturalis and Odostomia spermatophores (Gastropoda: Pyramidellidae)". American Philosophical Society Yearbook. 1967: 368–370.
