Paraonidae

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Paraonidae
Levinsenia gracilis

Levinsenia gracilis

Systematics
Empire : Animals (Animalia)
Trunk : Annelids (Annelida)
Class : Polychaete (Polychaeta)
Subclass : Scolecida
Order : Orbiniida
Family : Paraonidae
Scientific name
Paraonidae
Cerruti , 1909

Paraonidae is the name of a family of Vielborstern (Polychaeta), which are found in oceans worldwide as detritus from the coast to the deep sea.

features

The Paraonidae are small, mostly uniformly yellow to brown poly-bristles that reach lengths of 2 mm to 4 cm and have up to 200 segments. They have an elongated, thread-shaped and mostly sinuous body with a well-developed, truncated cone-shaped prostomium , on the upper side of which in most species sits a single central antenna and which often also has a pair of eyes . Laterally behind it has retractable, kidney-shaped nuchal organs and at the front edge a retractable sensory papilla. The peristomium , on the other hand, is poorly developed and in adults only consists of the underside area around the mouth. The body consists of a front part without gills, a slightly wider middle section with gills , where the parapodia are best developed and which can be slightly flattened dorsoventrally, and a gillless rear end. The anal lobe is beveled on the back and usually carries two to three cirrus .

The parapodia are two-branched, but both branches are weakly developed and have no aciculae. The lobe behind the bristles of the notopodium is long and cirrus-shaped to leaf-like, the lobe behind the bristles of the neuropodium is often smaller and more rounded, but not present in the posterior part of the body. The cirrus-shaped to ribbon-like gills arise on the back above the parapodia. Cross rows of cilia run along the gill-bearing segments . There are capillary-like bristles all over the body, as well as more specialized bristles, especially in the back of the body.

Its 2 to 10 μm thick cuticle covers an epithelium that is very glandular, especially behind each parapodia and on the ventral side.

The Paraonidae mostly have a non-muscular, but evertable, axially located pharynx , while this is muscular in the larval stage and changes during metamorphosis . On the belly side, it opens into a mouth that is surrounded by lips, the side lips being ciliated.

The intestinal canal is a straight tube made up of the oral cavity, pharynx, esophagus and the actual intestine. The closed blood vessel system is well developed, but has no central heart. The gills, whose breathing is supported by the flapping of eyelashes on and between the gills, are supplied by two powerful blood vessels that branch into capillaries and through which red or reddish-yellow blood flows. The nephridia are formed as metanephridia.

habitat

The Paraonidae are distributed in seas worldwide from the shore zone to depths of 6000 m. They live on soft sediment, sand, and mud.

Development cycle

The Paraonidae are separate sexes. The gametes are formed in the posterior segments behind the gills and are released to the outside by tearing the body wall. At least in the species Paradoneis armata , epitokes with enlarged eyes and bristles that are wider for swimming have been observed. Little is known about the development of the larvae, but there are probably both species with direct development of the eggs into crawling worms and those with indirect development via free-swimming larvae.

nutrition

As far as is known, the Paraonidae graze with their pharynx microorganisms on the substrate, which can be chamberlings , diatoms , dinoflagellates and bacteria .

Genera

The Paraonidae family is divided into 8 genera :

literature

  • Stanley J. Edmonds: Fauna of Australia, Volume 4A. Polychaetes & Allies. The Southern Synthesis 4. Commonwealth of Australia, 2000. Class Polychaeta. Pp. 107-110, Family Paraonidae.

Web links

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

Individual evidence

  1. ↑ Paraonidae Cerruti, 1909. WoRMS , 2018. Retrieved November 19, 2018.