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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 or 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.

The family is currently divided into 11 subfamilies (Ponder & Lindberg 1997).^[4] An alternative interpretation is that the family Pyramidellidae is but one of six families within the superfamily Pyramidelloidea (Schander, van Aartsen & Corgan 1999).^[5] 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):^[4]

• 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):^[5]

• Superfamily Pyramidelloidea Gray, 1840
  • Family Amathinidae Ponder, 1987
  • Family Ebalidae War?n, 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):^[6]

• Subfamily Pyramidellinae Gray, 1840
  • Tribe Pyramidellini Gray, 1840 - synonyms: Obeliscidae A. Adams, 1863 (inv.); Plotiidae Focart, 1951 (inv.)
  • Tribe Sayellini Wise, 1996 - formerly subfamily Sayellinae
• Subfamily Odostomiinae Pelseneer, 1928
  • Tribe Odostomiini Pelseneer, 1928 - synonyms: Ptychostomonidae Locard, 1886; Liostomiini Schander, Halanych, Dahlgren & Sundberg, 2003 (n.a.)
  • Tribe Chrysallidini Saurin, 1958 - formerly subfamily Chrysallidinae, synonyms: Menesthinae Saurin, 1958; Pyrgulininae Saurin, 1959
  • Tribe Cyclostremellini D. R. Moore, 1966 - formerly subfamily Cyclostremellinae
  • Tribe Odostomellini Saurin, 1959 - formerly subfamily Odostomellinae
• Subfamily Syrnolinae Saurin, 1958 - formerly subfamily Syrnolinae
  • Tribe Syrnolini Saurin, 1958
  • Tribe Tiberiini Saurin, 1958 - formerly subfamily Tiberiinae
• Subfamily Turbonillinae Bronn, 1849
  • Tribe Turbonillini Bronn, 1849 - synonym: Chemnitziinae Stoliczka, 1868
  • Tribe Cingulinini Saurin, 1958 - formerly subfamily Cingulininae
  • Tribe Eulimellini Saurin, 1958 - formerly subfamily Eulimellinae

In 2010 the family Pyramidellidae has been recognized as monophyletic ^[7]

Problematic genera

• Contraxalia Laseron, 1956^{[citation needed]}
• Cossmannica Dall & Bartsch, 1904^{[citation needed]}
• Eulimotibera Nomura, 1939^{[citation needed]}
• Morrisonetta Brandt, 1968^{[citation needed]}
• Peristichia Dall, 1889^[8]
• Ulfa Dall & Bartsch, 1904^{[citation needed]}
• Vagna Dall & Bartsch, 1904^{[citation needed]}

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. ^[9]

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.^[10][11] A few species in the family Pyramidellidae, such as Otopleura mitralis, are symbiotic with sea anemones, such as Neoaiptasia morbilla ^[12]

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.^{[13] [14] [15]}

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. ^[9]

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.^[10][11] A few species in the family Pyramidellida e, such as Otopleura mitralis, are symbiotic with sea anemones, such as Neoaiptasia morbilla ^[12]

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.^{[13] [14] [15]}

References

The Family Pyramidellidae is a member of the Superfamily Pyramidelloidea. Here is the complete "parentage" of Pyramidellidae:

• Domain: Eukaryota Whittaker & Margulis,1978 - eukaryotes
  • Kingdom: Animalia C. Linnaeus, 1758 - animals
    • Subkingdom: Bilateria (Hatschek, 1888) Cavalier-Smith, 1983 - bilaterians
      • Branch: Protostomia Grobben, 1908 - protostomes
        • Infrakingdom: Lophotrochozoa - Lophotrochozoans
          • Superphylum: Eutrochozoa
            • Phylum: Mollusca (C. Linnaeus, 1758) Cuvier, 1795 - Molluscs
              • Class: Gastropoda Cuvier, 1795 - Snails and Slugs
                • Subclass: Orthogastropoda Ponder & Lindberg, 1996
                  • Superorder: Heterobranchia J.E. Gray, 1840
                    • Order: Heterostropha P. Fischer, 1885
                      • Superfamily: Pyramidelloidea J.E. Gray, 1840
                        • Family: Pyramidellidae J.E. Gray, 1840