Apertural view of a shell of Pyramidella acus
Scientific classification
Kingdom: Animalia
Phylum: Mollusca
Class: Gastropoda
Clade: Heterobranchia
Clade: Euthyneura
Clade: Panpulmonata
Superfamily: Pyramidelloidea
Family: Pyramidellidae
J. E. Gray, 1840[1]

See text

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.[2]

This family of micromollusks has been little studied and the phylogenetic relationships within the family are not well worked out. There is a 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.[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]

The family is currently divided into 11 subfamilies (Ponder & Lindberg 1997).[5] An alternative interpretation is that the family Pyramidellidae is but one of six families within the superfamily Pyramidelloidea (Schander, van Aartsen & Corgan 1999).[6] Many species are rare or infrequently recorded.


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):[5]

1999 taxonomy

Taxonomy of Pyramidellidae by Schander, Van Aartsen & Corgan (1999):[6]

2005 taxonomy

Taxonomy of Pyramidellidae by Bouchet & Rocroi (2005):[7]

In 2010 the family Pyramidellidae has been recognized as monophyletic [8]

Problematic genera

The following genera are currently difficult to place within existing subtaxa of the Pyramidellidae.


The following genera have become synonyms (but some species in this genera have not yet been reassigned) :


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. [10]

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.[11][12] A few species in the family Pyramidellidae, such as Otopleura mitralis, are symbiotic with sea anemones, such as Neoaiptasia morbilla [13]

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.[14] [15] [16]

Name derived from shape

The name of this taxonomic family comes from the shape of the shell, which is like a pyramid.[17] More specifically, the shape is like a right circular cone,[18] which is equivalent to a right pyramid whose base has many sides.[19]


  1. Gray, J. E. (1840). Synopsis of the contents of the British Museum, 42nd edition. London. p. 370 pp.
  2. Schander C.; Halanych K.M.; Dahlgren T.; Sundberg P (May 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.
  3. Schander C., Hori S. & Lundberg J. (1999), 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
  4. Angela Dinapoli, Carmen Zinssmeister and Annette Klussmann-Kolb (2010), New insights into the phylogeny of the Pyramidellidae (Gastropoda), Journal of Molluscan Studies Volume 77, Issue 1 Pp. 1-7
  5. 1 2 Ponder, W.F. & Lindberg, D. R. (1997). "Towards a phylogeny of gastropod molluscs: an analysis using morphological characters". Zoological Journal of the Linnean Society. 119 (2): 88–265. doi:10.1111/j.1096-3642.1997.tb00137.x.
  6. 1 2 Schander C., van Aartsen J. J. & Corgan, J. C. (1999). "Families and genera of the Pyramidelloidea (Mollusca: Gastropoda)". Bollettino Malacologico. 34 (9–12): 145–166.
  7. Bouchet, P. & Rocroi, J.-P. (2005). "Classification and Nomenclator of Gastropod Families". Malacologia. 47 (1–2): 1–397.
  8. Dinapoli, Angela; Carmen Zinnsmeister; Annette Klussmann-Kolb (10 September 2010). "New insights into the phylogeny of the Pyramidellidae (Gastropoda)". Journal of Molluscan Studies. 77 (1): 1–7. doi:10.1093/mollus/eyq027. Retrieved 2011-10-25.
  9. WoRMS (2010). Peristichia. In: Bouchet, P.; Gofas, S.; Rosenberg, G. (2010) World Marine Mollusca database. Accessed through: World Register of Marine Species at on 2011-03-15
  10. J.J. van Aartsen, E. Gittenberger & J. Goud, Pyramidellidae (Mollusca, Gastropoda, Heterobranchia) collected during the Dutch CANCAP and MAURITANIA expeditions in the south-eastern part of the North Atlantic Ocean (part 2)
  11. Sneli, J.-A. (1972). "Odostomia turrita found on Hommarus gammarus". Nautilus. 86 (1): 23–24.
  12. Robertson, R.; Mau-Lastovicka, Terry (1979). "The ectoparasitism of Boonea and Fargoa (Gastropoda: Pyramidellidae)". Biological Bulletin. Marine Biological Laboratory. 157 (2): 320–333. doi:10.2307/1541058. JSTOR 1541058.
  13. Roger H. Goodwill et. al. (2009), A sea anemone symbiotic with gastropods of eight species in the Mariana Islands; Micronesica 41(1): 117–130, 2009
  14. Høisæter, T. (1965). "Spermatophores in Chrysallida obtusa (Brown) (Opisthobranchia, Pyramidellidae)". Sarsia. 18: 63–68.
  15. Robertson, R. (1967). "The life history of Odostomia bisuturalis and Odostomia spermatophores (Gastropoda: Pyramidellidae)". American Philosophical Society Yearbook. 1967: 368–370.
  16. Schander C., Hori, S., Lundberg, J. (1999). "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.
  17. Tenney, Sanborn and Tenney, Abby. Natural history of animals; Containing brief descriptions of the animals figured on Tenney's Natural history tablets, but complete without the tablets, p. 202 (Scribner, Armstrong & Co., 1875): "The Pyramid-Shells are so named from their shape"
  18. Step, Edward. Shell Life: An Introduction to the British Mollusca, p. 250 (F. Warne & Company, 1901).
  19. Robbins, Edward. Plane and Solid Geometry, p. 349 (American Book Company, 1907).

Further reading

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