Pyramidellidae


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 regarding which species belong to a specific genus or subgenus, contributing to much confusion. Schander 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.. However a study in 2011 seems to indicate that this family is deeply nested within the Pulmonata instead of the Heterobranchia.
The family is currently divided into 11 subfamilies. An alternative interpretation is that the family Pyramidellidae is but one of six families within the superfamily Pyramidelloidea. 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.

1997 taxonomy

Taxonomy of Pyramidellidae by Ponder & Lindberg :
Taxonomy of Pyramidellidae by Schander, Van Aartsen & Corgan :
Taxonomy of Pyramidellidae by Bouchet & Rocroi :
In 2010 the family Pyramidellidae has been recognized as monophyletic
In 2017 the genus Helodiamea Peñas & Rolán, 2017 of deep-water Pyramidelloidea from the Central and South Pacific, was recognized.

Problematic taxa

The following genera are currently difficult to place within existing subtaxa of the Pyramidellidae.
The following species is of uncertain placement within Pyramidellidae.
The following genera have become synonyms :
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 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 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 oligogyrous 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.
The species are characterized by the lack of jaw or radula, because they are ectoparasites.

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, a lobed process called the mentum 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.