Pyramidellidae, common name the pyram family, or pyramid shells, is a voluminous taxonomic family of mostly small and minute ectoparasitic sea snails, marine heterobranch gastropod molluscs. The great majority of species of pyrams are micromolluscs.
The pyram family is distributed worldwide with more than 6,000 named species in more than 350 nominal genera and subgenera.
This family of micromollusks has been little studied and the phylogenetic relationships within the family are not well worked out. There is an absence of a general consensus which species belong to a specific genus or subgenus, contributing to much confusion. Schander (1999) names more than 300 supraspecific names. 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.
The family is currently divided into 11 subfamilies (Ponder & Lindberg 1997). An alternative interpretation is that the family Pyramidellidae is but one of six families within the superfamily Pyramidelloidea (Schander, van Aartsen & Corgan 1999). 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).
1997 taxonomy
Taxonomy of Pyramidellidae by Ponder & Lindberg (1997):
Chrysallidinae Saurin, 1958
Cingulininae Saurin, 1959
Cyclostremellinae Moore, 1966
Eulimellinae Saurin, 1958
Odostomellinae Saurin, 1959
Odostomiinae Pelseneer, 1928
Pyramidellinae J.E. Gray, 1840
Sayellinae Wise, 1996
Syrnolinae Saurin, 1958
Tiberiinae Saurin, 1958
Turbonillinae Bronn, 1849
1999 taxonomy
Taxonomy of Pyramidellidae by Schander, Van Aartsen & Corgan (1999):
Superfamily Pyramidelloidea Gray, 1840
Family Amathinidae Ponder, 1987
Family Ebalidae Warén, 1994 - synonym: Anisocyclidae van Aartsen, 1995
Family Odostomiidae Pelseneer, 1928
Subfamily Odostomiinae Pelseneer, 1928
Subfamily Chrysallidinae Saurin, 1958
Subfamily Odostomellinae Saurin, 1958
Subfamily Cyclostremellinae Moore, 1966
Family Pyramidellidae J. E. Gray, 1840
Subfamily Pyramidellinae J. E. Gray, 1840
Subfamily Sayellinae Wise, 1996
Family Syrnolidae Saurin, 1958
Subfamily Syrnolinae Saurin, 1958
Subfamily Tiberiinae Saurin, 1958
Family Turbonillidae Bronn, 1849
Subfamily Turbonillinae Bronn, 1849
Subfamily Eulimellinae Saurin, 1958
Subfamily Cingulininae Saurin, 1959
2005 taxonomy
Taxonomy of Pyramidellidae by Bouchet & Rocroi (2005):
Partulida Schaufuss, 1869: synonym of Chrysallida Carpenter, 1856
Planipyrgiscus [sic] accepted as Planpyrgiscus Laws, 1937
Plotia Röding, 1798: synonym of Pyramidella Lamarck, 1799
Ptychostomon Locard, 1886 accepted as Odostomia Fleming, 1813
Pyrgulina A. Adams, 1864: synonym of Chrysallida Carpenter, 1856
Raoulostraca Oliver, 1915 accepted as Eulimella Forbes & M'Andrew, 1846
Tragula Monterosato, 1884: synonym of Chrysallida Carpenter, 1856
Tropeas [sic] accepted as 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.
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 columella has usually one, but sometimes several, spiral folds. The aperture is closed by an operculum.
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.
Life habits
The Pyramidellidae are ectoparasites, feeding mainly on other molluscs and on annelid worms, but some are known to feed on peanut worms and crustaceans. A few species in the family Pyramidellidae, such as Otopleura mitralis, are symbiotic with sea anemones, such as Neoaiptasia morbilla
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.
These gastropods are hermaphrodites, laying eggs in jelly-like masses on the shell of its host. Some species have spermatophores.
Name derived from shape
The name of this taxonomic family comes from the shape of the shell, which is like a pyramid. More specifically, the shape is like a right circular cone, which is equivalent to a right pyramid whose base has many sides.
