Sigalionidae

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Sigalionidae
Sigalion mathildae

Sigalion mathildae

Systematics
Empire : Animals (Animalia)
Trunk : Annelids (Annelida)
Class : Polychaete (Polychaeta)
Subclass : Aciculata
Order : Phyllodocida
Family : Sigalionidae
Scientific name
Sigalionidae
Kinberg , 1856

Sigalionidae is the name of a family to medium-sized, mostly grave forming, presumably mostly very small predatory living polychaete (Polychaeta), whose about 180 species are found in oceans worldwide.

features

The Sigalionidae usually have a long and narrow body, tapering at the back, with a rectangular cross-section and up to over 300 distinct segments . Similar to the Polynoidae , the back of the mostly much longer Sigalionidae is more or less densely covered with scale-shaped elytra, which in some species, especially in the genus Psammolyce , are densely covered with sand. The ventral side can be smooth or covered with papillae.

The Sigalionidae have a well-developed head with many appendages as well as well-developed parapods and bristles . The oval or rectangular, front blunt or rounded Prostomium is forward and merged with the first segment laterally and carries forward most three antennae - a pair of antennas and usually also a center antenna - and ventral a pair of long, tapered tentacle - cirri , also a pair of rounded, ciliate nuchal organs and usually one or two pairs of eyes , which are missing in some Leanira species in the deep sea mud . The side antennas start at the prostomium, but can be fused with the parapodia of the first segment. The peristomium is reduced to lips around the mouth. The palps sit on the stomach side, taper and are not articulated; at the base they are merged with the parapodies of the first segment. The tentacle carriers of the first segment each have a single acicula, bristles on the notopodia, and a pair of dorsal and ventral, forward-facing tentacle cirrus. The first segment curves around the head and is fused to the prostomium at the base. The first segment carries two pairs of tentacle cirrus and one pair of parapodia.

The parapodies of all segments are two-branched, and the neuropodia are longer than the notopodia. Dorsal and ventral cirrus are present. At the anterior end, dorsal cirrus alternates with elytra. In some species there are dorsal cirrus on the 3rd segment, which taper, while in others there are neither elytra nor dorsal cirrus on the 3rd segment. The pygidium carries a pair of cirrus.

On the segments 2, 4, 5 and 7, from the 8th to 25th or 27th segment on alternate segments and on the rear part of the body then on each segment there are numerous pairs of elytra. These can have smooth or papillae margins, and their surface can be smooth or covered with microtubercles. On all segments without elytra there are dorsal tubercles. With the exception of a few segments on the front part of the body, there are ciliate, finger-shaped processes that serve as gills on the sides of the elytra and the dorsal tubercles . The Sigalionidae can elevate their elytra so that they form a pair of breathing channels above the parapodia where the gills are located. On the back of the notopodium sit three cup-shaped ciliate ctenidia that form ciliate grooves along the dorsolateral parts of the body.

The longitudinal muscles are arranged in bundles. Aciculae are present. On the parapodia there are composite bristles that taper to fine tips or are serrated or sickle-shaped distally. The shafts and appendages of the bristles have joints with a single ligament. Other bristles are capillary-shaped with various decorations.

The buccal organ is designed as an axially lying, muscular, evertable pharynx , on two pairs of dorsoventrally aligned, interlocking jaws and a ring of end papillae around the mouth. A throat membrane is missing and the intestine has blind sacs arranged segmentally. There are paired mixonephridia in most of the segments . The closed blood vessel system has no central heart.

distribution

The Sigalionidae occur in oceans worldwide from the intertidal zone to the deep sea, but also in estuaries , albeit rarely in large numbers. They usually live on soft sediment soils or in shallow waters on seagrass beds . A few small species, which lack notopodia and elytra and which are chosen to belong to the genus Metaxypsamma , live in sand gap systems . Most species, however, dig through mud and sand at high speeds. Unlike most species, the Thalenessa oculata, which lives in the intertidal zone, lies flat in the sand, in which it digs itself by rotating its parapodia. Few species, such as the genus Sthenelanella , form living tubes from threads that are produced by the spinneret on the notopodia.

nutrition

The diet of the Sigalionidae has not yet been researched. Due to the muscular, evertable pharynx with four jaws, it is assumed that they are carnivores .

Development cycle

Little is known about the reproduction of the Sigalionidae. Sthenelais boa is separate from the sexes and releases its gametes into the open sea water, where fertilization takes place. Free-swimming larvae develop from the zygotes and feed on phytoplankton until they sink and metamorphose into crawling worms .

Genera

The approximately 180 species of the Sigalionidae family belong to 29 genera :

Pelogeniinae Pettibone, 1997
without subfamily

The genus Pholoe , which previously belonged to this family and comprises around 10 species, is now placed in its own family Pholoidae .

literature

  • Stanley J. Edmonds: Fauna of Australia, Volume 4A. Polychaetes & Allies. The Southern Synthesis 4. Commonwealth of Australia, 2000. Class Polychaeta. Pp. 211-214, Family Sigalionidae.

Web links

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

Individual evidence

  1. ↑ Sigalionidae Kinberg, 1856. WoRMS , 2018. Accessed December 12, 2018.