Cossura

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Cossura
Cossura pygodactylata

Cossura pygodactylata

Systematics
Trunk : Annelids (Annelida)
Class : Polychaete (Polychaeta)
Subclass : Scolecida
Order : Cossurida
Family : Cossuridae
Genre : Cossura
Scientific name of the  order
Cossurida
Fauchald , 1977
Scientific name of the  family
Cossuridae
Day , 1963
Scientific name of the  genus
Cossura
Webster & Benedict , 1887

In the genus Cossura that simultaneously the mono generic family Cossuridae forms, is a group of Vielborstern (Polychaeta), which are found in oceans worldwide as detritus from the coast to the deep sea. Heterocossura and Cossurella , which were at times run as separate genres, were synonymous with Cossura in 2000 .

features

The Cossuridae are small, thread-like annulus worms with numerous distinct segments . They have a blunt head with no attachments and a single, long, thread-like gill that sits on the back on one of the front segments.

The prostomium is bluntly conical, the peristomium, on the other hand, a clearly separated ring, which is sometimes referred to as a "bristle-free segment". The two nuchal organs are a pair of short, ciliate grooves that sit dorso-laterally at the posterior end of the prostomium. The longitudinal muscles are arranged in bundles. The first segment and its appendices are similar to the following segments. The parapodia are similar branches that converge at the first or the first segments and on which capillary-shaped bristles sit. Both the notopodia and the neuropodia are low and rib-shaped or papilla-like, and both dorsal and ventral cirrus are absent, as is epidermal papillae. In some species, however, there are three or more anal cirrus on the pygidium. Aciculae are always absent, and the bristles are fringed, slender capillary-like, with spiked bristles only being present on the posterior segments in the genus Cossurella.

The intestinal canal is a straight tube and lacks a throat membrane. The closed blood vessel system has a poorly developed back vessel with connection to the intestinal vascular plexus and two clearly recognizable blood vessels in the back gill, while a central heart is missing.

The thin body wall has only a weakly developed muscle layer. The front part of the body, the thorax, is more muscular than the back part, the abdomen. In the Cossura longocirrata , the thorax consists of about 20 to 22 bristle-bearing segments and has a diameter of 350 to 400 μm. In mature females of this species, the abdomen consists of 35 to 43 segments and is 4 to 5 mm long. The epidermis here is about 4 to 5 μm thick, plus a cuticle about 1 μm thick.

Development cycle

The Cossuridae are probably mostly or exclusively sexually separated, in some cases possibly protandric hermaphrodites, and develop their gametes in the more posterior segments of the body. Mature egg cells are around 100 to 130 μm in size and contain three types of yolk granules. Young animals are only known from Cossura pygodactylata in the French bay of Arcachon , where exclusively benthic young animals, almost identical to the adults , were observed in the upper 2 cm of the mud with a high organic content. At times, there are up to 32,000 juveniles per m 2 , but decrease their numbers in the next few weeks dramatically.

distribution and habitat

The Cossuridae live in sandy mud at depths from the shallow areas of the intertidal zone to the deep sea . They do not build solid tubes, but rather fragile tubes of mucus to which sediment particles adhere. When the animals are pulled out of the sediment, they usually break and die.

nutrition

The Cossuridae are detritus eaters , with 15 strongly ciliated tentacles sitting on their evertable buccal organ on the roof of the buccal cavity . They also differ from tentacles of other polychaete families in that they have neither coelom spaces nor spinal muscles and therefore cannot be hydraulically extended or contracted. The cilia sitting on them can, however, generate a flow of food that swirls food particles into the open mouth.

Systematics

Harrison E. Webster and James E. Benedict described the genus Cossura at the same time as the type species Cossura longocirrata in 1887 , which was initially counted among the vine worms (Cirratulidae). John H. Day (1963) raised the genus Cossura to a separate monogeneric family, Cossuridae with the characteristic feature of a single thread-like gill on the back. While Kristian Fauchald granted them their own Cossurida order in 1977, Gregory Rouse and Kristian Fauchald placed them in the Scolecida order in 1997. In 1976, Olga Hartman established a separate genus Cossurella for the species found at the time in the Indian Ocean with spiked bristles on the rear segments . However, Geoffrey B. Read synonymized this genus with Cossura in 2000 .

species

There are 28 species in the genus Cossura :

literature

  • Harrison E. Webster, James E. Benedict (1887): The Annelida Chaetopoda, from Eastport, Maine. US Commission of Fish & Fisheries. Report of the United States Commissioner of Fisheries 1885, part 13, II. Appendix to report of commissioner, D.22, pp. 707-758, here p. 743. Cossura ng, Cossura longocirrata , n. Sp. Panels 1–8 ( download pdf ).
  • Olga Hartman (1976): Polychaetous annelids of the Indian Ocean including an account of species collected by members of the International Indian Ocean Expeditions, 1963–1964 and a catalog and bibliography of the species from India. Journal of Marine Biological Association of India 16 (1), pp. 191-252, here p. 234.
  • R. Michael Ewing (1987): Review of the genus Cossurella (Polychaeta: Cossuridae) including descriptions of two new species and a key to the species of the world. Bulletin of the Biological Society of Washington, 7: 3-10.
  • Stanley J. Edmonds: Fauna of Australia, Volume 4A. Polychaetes & Allies. The Southern Synthesis 4. Commonwealth of Australia, 2000. Class Polychaeta. Pp. 93-96, Family Cossuridae.
  • Geoffrey B. Read (2000): Taxonomy and distribution of a new Cossura species (Annelida: Polychaeta: Cossuridae) from New Zealand. Proceedings of the Biological Society of Washington 113 (4), pp. 1096-1110.

Web links

Commons : Cossuridae  - Collection of images, videos and audio files

Individual evidence

  1. ↑ Cossura Webster & Benedict, 1887 WoRMS , 2018. Accessed December 11, 2018th