| Hydrobiidae | |
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| Peringia ulvae | |
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Gastropoda |
| Subclass: | Caenogastropoda |
| Order: | Littorinimorpha |
| Superfamily: | Truncatelloidea |
| Family: | Hydrobiidae Stimpson, 1865 |
| Synonyms | |
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Hydrobiidae, commonly known as mud snails, is a large cosmopolitan family of very small freshwater and brackish water snails with an operculum; they are in the order Littorinimorpha. [1]
Hydrobiidae are found in much of the world, inhabiting all continents except Antarctica. In Australia alone there are over 260 species in the family. [2]
These are very small or minute snails, with a shell height of less than 8 mm. The dextrally-coiled shells are smooth (except for growth lines conforming to the shape of the outer lip) and are usually rather nondescript. The shell offers very few robust characteristics to the systematist who is attempting to classify the species within this family. This difficulty is compounded by a high degree of intraspecific variation. Descriptions often have to be based on the characteristics of the operculum, radula and penis.
The shell of species within this family varies from planispiral to needle-shaped. The shell may have an open umbilicus or a plugged umbilicus. The thickness of the shell can vary from thin to fairly solid. The shell may be transparent and horn-colored, or colorless.
The number of whorls in the shell varies between two and eight. The shell can sometimes even assume a corkscrew or hornlike shape by loosening of the attachment of body whorl. The periostracum (outer layer of the shell) is usually thin, and is often colored. It can sometimes show hair-like projections.
The sinuous aperture is entire, not interrupted by a siphonal canal or other extensions. It is sometimes thickened. The protoconch is usually shaped like a dome, and usually shows a few spirals.
The corneous operculum is usually well-formed and shows only a few spirals.
The head, foot, mantle and visceral coil are colored pale gray to dark purple-black with melanin pigments. Subterranean species are often unpigmented.
The strong foot can be retracted into the shell. The mucous glands are situated at the anterior edge of the foot. There are no posterior mucous glands. The symmetrical cephalic tentacles are threadlike, with blunt or rounded tips. The eyes are located at the base of the tentacles.
The ctenidium (a comblike respiratory apparatus) goes along most of the length of the pallial cavity. This respiratory gill consists of 10 to 200 triangular filaments. The osphradium, the olfactory organ linked with the respiration organ, is usually relatively small.
The taenioglossate radula consists of more than fifty rows of teeth. The central tooth is trapezoidal. The lateral teeth have few to numerous cusps. The marginal teeth are usually with numerous cusps.
The species usually have both male and female individuals, but very rarely reproduction may be parthenogenic, caused by internal fertilization. The females lay eggs in single capsules on the leaves or stems of water plants. But sometimes they produce eggs that are hatched within the pallial gonoduct of the body, and in these cases the young are born alive. Species that inhabit estuaries sometimes produce veliger larvae.
The fossil record of this family extends back to the Early Carboniferous. [3]
Most species of this family live in freshwater (lakes, ponds, rivers, streams), but some are found in brackish water or at the borders between freshwater and brackish water. A few occur in marine environments on sandy or muddy bottoms between algae and sea grass.
This is the largest family within the superfamily Truncatelloidea. At one time or another some 400 genera have been assigned to this family, and probably more than 1,000 species. [3] The Hydrobiidae family is the most widespread and diverse family of freshwater molluscs in the world, occupying a range of habitats from streams and estuarine creeks to alpine bogs.
This family was originally named by Troschel in 1857, as the group Hydrobiae. Troschel was not certain of their rank, and he placed them in the Taenioglossata: Ctenobranchiata between the Lithoglyphi and Ancyloti. [3] Over the years there have been numerous attempts to give an adequate and more finely divided classification. Thiele (1925, 1929 and 1931) set up the most comprehensive classification, with a review of the family at generic level.
Notable works about taxonomy of Hydrobiidae includes works by Radoman, for example Radoman (1983). [4]
The classification, as specified by Kabat and Hershler (1993), [3] does not form a monophyletic group, and was in need of revision.
A study by Wilke et al. (2001) [5] using molecular data from COI (Cytochrome c oxidase subunit I) and 18S genes has resulted in a new tentative set of subfamilies: Hydrobiinae, Pseudamnicolinae, Nymphophilinae, Islamiinae and Horatiinae.
The following subfamilies are recognized in the gastropod taxonomy of Bouchet & Rocroi from 2005: [6]
The Amnicolidae and Cochliopidae are considered as distinct families according to the taxonomy of Bouchet & Rocroi (2005). [6]
Gyraulus is a genus of small, mostly air-breathing, freshwater snails, aquatic pulmonate gastropod mollusks in the family Planorbidae, the ram's horn snails.
Alzoniella is a genus of minute freshwater spring snails, aquatic gastropod mollusks or micromollusks in the subfamily Islamiinae of the family Hydrobiidae.
Belgrandiella is a genus of minute freshwater snails with a gill and an operculum, aquatic gastropod mollusks in the family Hydrobiidae.
Bythinella is a genus of very small freshwater snails, an aquatic gastropod mollusk in the family Bythinellidae.
Pseudamnicola is a genus of small brackish water snails with an operculum, aquatic gastropod mollusks in the subfamily Pseudamnicolinae of the family Hydrobiidae.
Theodoxus is a genus of nerites, small water snails with an operculum, some of which live in freshwater, and some in both freshwater and brackish water, aquatic gastropod mollusks in the family Neritidae, the nerites.
Islamia is a genus of small freshwater snails with a gill and an operculum, aquatic gastropod mollusks in the family Hydrobiidae.
Pyrgula is a genus of freshwater snail with a gill and an operculum, an aquatic gastropod mollusk in the family Hydrobiidae.
Navarriella elliptica is a species of very small aquatic snail, a spring snail, an operculate gastropod mollusc in the family Hydrobiidae.
Truncatelloidea is a superfamily of snails, gastropod mollusks in the clade Caenogastropoda.
Horatia is a genus of gastropod molluscs, comprising a small group of minute stygobiont freshwater snails with valvatoid shells, belonging to the subfamily Horatiinae of the family Hydrobiidae.
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