Worm snails

from Wikipedia, the free encyclopedia
Worm snails
Thylacodes squamigerus in situ

Thylacodes squamigerus in situ

Systematics
Superordinate : Caenogastropoda
Order : Sorbeoconcha
Subordination : Hypsogastropoda
Partial order : Littorinimorpha
Superfamily : Vermetoidea
Family : Worm snails
Scientific name
Vermetidae
Rafinesque , 1815

The worm screw (Vermetidae) are a family from the group of Caenogastropoda with irregular, tubular-shaped worm-grown housings fixed to bedrock in warmer and warm seas of all three major oceans are common. They feed the filter feeders of plankton .

features

The worm snails differ greatly from other shell snails in the shape of their snail shells , which consist of an irregularly wound tube and are therefore often confused with the lime dwellings of tube- forming polychaetes, especially of the Serpulidae family . They differ from these mainly in the three layers typical of mollusc shells , of which the innermost, mother-of-pearl (Hypostracum), has a clear sheen, while the annelid tubes are only two-layered and matt on the inside. Most of these tubular snail shells are fixed to the rocky substrate by a cement-like substance, and in many species also to conspecifics, so that colony formation occurs. In adult worm snails, the mouth of the shell is exposed and is usually directed upwards. An operculum can be present or absent; it is often only half the diameter of the tube. If necessary, damaged sections of the tubular house are separated by a chalky septum and thus abandoned. The shape of the house varies greatly within the family and often within a species, which makes it difficult to determine.

The worm snails feed on detritus and plankton , which are filtered out of the seawater that flows in with the help of the gills , whereby a mucous web produced by the foot is often used to catch the food particles.

Worm snails are separate sexes, with the males being aphallic, meaning they have no penis. The spermatophores are released into the open water during mating and are caught by the female's mucous network, which also serves as food, and transferred to the female sexual opening for internal fertilization. The fertilized females release the egg capsules into their mantle cavity in order to incubate them there. In many species, such as the genus Vermetus , free-swimming Veliger larvae hatch from the capsules , which after a pelagic phase metamorphose into small snails as zooplankton . In the species Dendropoma petraeum, which lives in the western Mediterranean , up to 86 capsules are incubated at the same time, the highest number known to date in worm snails. One capsule contains one egg rich in yolk (rarely 2 or 3) and no scrub eggs. The development through the Veliger stage takes place in the capsule, so that finally finished small snails hatch out of the capsule, the protoconch of which measures up to a millimeter. This juvenile snail shell is still regularly coiled, but now the worm-shaped shell growth begins.

Genera

The following 14 genera belong to the Vermetidae family:

literature

Web links

Commons : Worm snails (Vermetidae)  - Collection of images, videos and audio files

Individual evidence

  1. ↑ Klaus Bandel (2006): Families of the Cerithioidea and related superfamilies (Palaeo-Caenogastropoda; Mollusca) from the Triassic to the Recent characterized by protoconch morphology - including the description of new taxa. Paläontologie, Stratigraphie, Fazies (14), Freiberger Forschungshefte, C 511, pp. 59–138, here p. 100.
  2. ↑ Marta Calvo Revuelta, J. Templado, Pablo E. Penchaszadeh (1998): Reproductive biology of the gregarious Mediterranean vermetid gastropod Dendropoma petraeum. Journal of the Marine Biological Association of the United Kingdom 78, pp. 525-549.
  3. ^ World Register of Marine Species , Vermetidae Rafinesque, 1815