|Malmgren , 1866|
Trichobranchidae is the name of a family of mostly small polychaeta (polychaeta) living in characteristic cone-shaped living tubes , which can be found as detritus eater in seas around the world .
The Trichobranchidae have a comparatively short and compact body and reach lengths of a few millimeters to about 10 cm. They have a clearly separated head and tail and, depending on the species, a fixed number of segments of the thorax on which both notopodia and neuropodia are located, while the number of segments of the abdomen on which only neuropodia are located is variable. While aciculae are absent, the remaining bristles are capillary-shaped or hook-shaped or beaked with a short or long shaft. Characteristic of the Trichobranchidae is the merging of the prostomium with the peristomium along the front edge of the former. The peristomium forms two enlarged lips, with the upper lip widening into lateral lobes and the lower lip being greatly enlarged into a ribbed, conical trunk that can be fully retracted. There are numerous non-retractable, comparatively short buccal tentacles of two types with eyelashes and an enlarged tentacle membrane on the prostomium. The gills are located on the back from the 2nd to the 4th segment and can be designed as simple threads, rosettes or individual stems with 2 to 5 leaf-like lobes. Nuchal organs are present in Trichobranchus , but absent in Terebellides . The pygidium is smooth or lobed and can carry small cirrus .
The pharynx lies ventrally and cannot be turned out. The intestine is looped and a throat membrane is present. The well-developed closed blood vessel system is equipped with a central heart . The blood has no blood cells; the high molecular weight blood pigment is dissolved in the plasma. The gills are well supplied with blood. The nephridia are formed as metanephridia. The first pair of nephridia serves as kidneys, while the subsequent ones presumably serve to discharge the gametes .
distribution and habitat
The Trichobranchidae are distributed in seas worldwide from the shore zones to depths of 2700 m. They live mainly in shallow waters in soft sediment in residential tunnels or digging, where they can occur in large numbers.
The Trichobranchidae are separate sexes, with both sexes being about equally common. There are only studies of reproductive biology for two northern European species. In the northern European species Trichobranchus glacialis , the maturation of the germ cells takes about 8 to 9 months. Egg-laying takes place in December and January, presumably in connection with external fertilization, and the embryos, which are supplied with yolk, develop directly into creeping worms. Terebellides stroemii lays its eggs in October and November in round, approximately 4 mm large jelly masses that are attached to the parental tube or dead Zostera plants. Spherical Trochophora larvae hatch, but they do not appear in the plankton, so they only swim for a very short time until metamorphosis . Terebellides stroemii lays eggs for the first time at the age of 2 and then does so once a year in its five-year lifespan.
The Trichobranchidae feed on detritus , which they pick up from the sediment with their tentacles and transport to the mouth through the action of the eyelashes or swallow it with the grains of sand.
Genera and species
The approximately 80 species of the Trichobranchidae family are divided into 3 genera :
- Octobranchus Marion & Bobretzky, 1875
- Terebellides Sars, 1835
- Trichobranchus Malmgren, 1866
- Stanley J. Edmonds: Fauna of Australia, Volume 4A. Polychaetes & Allies. The Southern Synthesis 4. Commonwealth of Australia, 2000. Class Polychaeta. Pp. 311-316, Family Trichobranchidae.
- ↑ Trichobranchidae Malmgren, 1866. WoRMS , 2018. Retrieved October 7, 2018.