Hydrocenidae is a poorly-known taxonomic family

Family (biology)

In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 of minute land snail

Land snail

A land snail is any of the many species of snail that live on land, as opposed to those that live in salt water and fresh water. Land snails are terrestrial gastropod mollusks that have shells, It is not always an easy matter to say which species are terrestrial, because some are more or less...

s or cave

Cave

A cave or cavern is a natural underground space large enough for a human to enter. The term applies to natural cavities some part of which is in total darkness. The word cave also includes smaller spaces like rock shelters, sea caves, and grottos.Speleology is the science of exploration and study...

 snails with an operculum

Operculum (gastropod)

The operculum, meaning little lid, is a corneous or calcareous anatomical structure which exists in many groups of sea snails and freshwater snails, and also in a few groups of land snails...

, terrestrial

Terrestrial animal

Terrestrial animals are animals that live predominantly or entirely on land , as compared with aquatic animals, which live predominantly or entirely in the water , or amphibians, which rely on a combination of aquatic and terrestrial habitats...

 gastropod mollusks or micromollusk

Micromollusk

A micromollusk is a descriptive term for a shelled mollusk which is extremely small, even at full adult size. The word is usually, but not exclusively, applied to marine mollusks, although in addition, numerous species of land snails and freshwater mollusks also reach adult size at very small...

s in the clade

Clade

A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...

 Cycloneritimorpha

Cycloneritimorpha

Cycloneritimorpha is a clade of land snails, freshwater snails, and sea snails. These are gastropod molluscs within the larger clade Neritimorpha...

.

These tiny cave snails are not closely related at all to the air-breathing or pulmonate land snails. These hydrocenid snails are more closely related to the marine and freshwater snails known as nerites, the Neritidae

Neritidae

Neritidae, common name the nerites, is a taxonomic family of small to medium-sized saltwater and freshwater snails which have a gill and a distinctive operculum, marine, brackish water and freshwater gastropod mollusks in the order Neritoida....

.

Hydrocenidae is the only family in the superfamily Hydrocenoidea. This family has no subfamilies according to the taxonomy of the Gastropoda by Bouchet & Rocroi, 2005

Taxonomy of the Gastropoda (Bouchet & Rocroi, 2005)

The taxonomy of the Gastropoda as it was revised by Philippe Bouchet and Jean-Pierre Rocroi is currently the most up-to-date overall system for classifying gastropod mollusks...

.

Description

The animal have no gill, but a pulmonary cavity. Tentacles are short and large. The eyes are prominent, situated at the upper or outer base of the tentacles. The foot is short, oval and obtuse. The denticle (tiny teeth) of radula

Radula

The radula is an anatomical structure that is used by molluscs for feeding, sometimes compared rather inaccurately to a tongue. It is a minutely toothed, chitinous ribbon, which is typically used for scraping or cutting food before the food enters the esophagus...

 have the formula ∞ 1, (1 + 1 + 1), 1 ∞. The central denticles are small and elongated. The lateral tooth is rather large, straight, without a cusp. The numerous lateral teeth are denticulate, and arranged in very oblique series.

The shell

Gastropod shell

The gastropod shell is a shell which is part of the body of a gastropod or snail, one kind of mollusc. The gastropod shell is an external skeleton or exoskeleton, which serves not only for muscle attachment, but also for protection from predators and from mechanical damage...

 is imperforate, conic and globular. Whorls

Whorl (mollusc)

A whorl is a single, complete 360° revolution or turn in the spiral growth of a mollusc shell. A spiral configuration of the shell is found in of numerous gastropods, but it is also found in shelled cephalopods including Nautilus, Spirula and the large extinct subclass of cephalopods known as the...

 are convex. The spire

Spire (mollusc)

A spire is a descriptive term for part of the coiled shell of mollusks. The word is a convenient aid in describing shells, but it does not refer to a very precise part of shell anatomy: the spire consists of all of the whorls except for the body whorl...

 is short. The peristome is continuous. The columella is callous. The lip is not reflexed. The operculum

Operculum (gastropod)

The operculum, meaning little lid, is a corneous or calcareous anatomical structure which exists in many groups of sea snails and freshwater snails, and also in a few groups of land snails...

 is calcareous, ornamented with striae which are concentric to the nucleus. The inner side od the operculum is with a prominent apophysis arising from the nucleus.

Genera

Genera and species within the family Hydrocenidae include:

• Genus Georissa
  Georissa
  Georissa is a genus of minute cave snails, terrestrial gastropod mollusks in the family Hydrocenidae.-Species:Species within the genus Georissa include:* Georissa bangueyensis* Georissa biangulata* Georissa borneensis...
  
  Blanford, 1884
• Genus Hydrocena Pfeiffer, 1841
  • Hydrocena cattaroense (Pfeiffer, 1841)
• Genus Omphalorissa Iredale
  Tom Iredale
  Tom Iredale was an English-born ornithologist and malacologist who had a long association with Australia, where he lived for most of his life. He was an autodidact who never went to university and lacked formal training...
  
  , 1933
  • Omphalorissa purchasi
    Omphalorissa purchasi
    Omphalorissa purchasi is a species of small land snail, a terrestrial gastropod mollusc in the family Hydrocenidae.The type specimen is stored in the Imperial Natural History Museum, Vienna.- Description :...
    
    (Pfeiffer, 1862)
• Monterissa
  Monterissa
  Monterissa is a genus of minute cave snails with an operculum, gastropod mollusks in the family Hydrocenidae.-References:*...
  
  Iredale, 1944
  • Monterissa gowerensis
    Monterissa gowerensis
    Monterissa gowerensis is a species of minute cave snails with an operculum, gastropod mollusks in the family Hydrocenidae.-References:* Ponder, W.F. & Stanisic, J 1996. . Downloaded on 7 August 2007....