Magelonidae

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Magelonidae
Magelona longicornis

Magelona longicornis

Systematics
Trunk : Annelids (Annelida)
Class : Polychaete (Polychaeta)
Subclass : Palpata
Order : Canalipalpata
Subordination : Spionida
Family : Magelonidae
Scientific name
Magelonidae
Cunningham & Ramage , 1888

Magelonidae is the name of a family of polychaeta (Polychaeta) burrowing in the sediment and living on detritus , of which around 67 species can be found in oceans worldwide. Long regarded as a monogeneric family with the only genus Magelona , a new species was found in 2001 and described in a new genus ( Octomagelona bizkaiensis ).

features

The Magelonidae have an elongated, thread-like body and a characteristic flattened, shovel-shaped prostomium , on which a pair of palps sits ventrolaterally , which have a round cross-section at the base and are provided with elongated papillae at the distal end. Nuchal organs are absent. The evertable pharynx (pharynx) lying under the esophagus has no jaws. The first segment has neither parapodia nor bristles in adults. On the other segments the parapodia are two-branched, and on each branch there is a low comb of bristles and supporting foot flaps. Dorsal and ventral cirrus muscles are absent, as are gills and aciculae. The bristles are simple capillary-shaped bristles and serrated hooks with hoods. The bristles on the 9th bost-bearing segment are spiky capillary bristles. A pair of cirrus is sitting on the pygidium. In the genus Magelona the first nine bristle-bearing segments form the thorax, in Octomagelona bizkaiensis the first eight bristle-bearing segments, while the abdomen consists of the following segments.

Among the annelids, the Magelonidae are characterized by peculiarities of pale purple blood and blood circulation. These include blood cells, which contain high molecular weight hemerythrin as a blood pigment . The closed blood vessel system is well developed, but has no central heart. The pharynx is everted by pumping blood into an extensive blood sinus at the anterior end. The dorsal vessel in the anterior segment of the annelid consists of chambers separated from one another by flaps, which regularly fill and empty and propel the blood forward into a very muscular, heart-like area of ​​the dorsal artery . In the posterior dorsal vessel, valves in the area of ​​the celomial septum prevent the blood from flowing back. The paired lateral vessels have pulsating, heart-like extensions in the posterior segments. The longitudinal muscles of the skin muscle hose show at the Magelonidae in its structural similarities with the muscles of nematodes .

Distribution, habitat and way of life

The Magelonidae are distributed worldwide on sedimentary soils in seas . With the help of their everted pharynx, alternating with movements of the prostomium, they dig passages through the sediment, which they line with the body's own mucus. However, they are not sediment eater, but graze the organic coating of detritus from the sediment surface with the help of their papillary palps. At the same time, the palps, which are well supplied with blood, are used for breathing.

Development cycle

Larva of Magelona papillicornis . From A monograph of the British marine annelids, 1915, panel XCIII.

The Magelonidae are separate sexes, but little is known about their reproduction. The fertilization probably takes place in the open sea water. The development takes place via a free-swimming larval stage in the zooplankton until the larva sinks and metamorphoses into a creeping worm .

Role of Magelona larvae as predators of mussel larvae

In an extensive study published in 1922 on the nutrition of marine plankton organisms in Plymouth , Marie Victoire Lebour observed that polychaete larvae usually eat mainly diatoms , while in the intestines of the larvae of Magelona (unspecified) she found only larvae of mussels . The ability of Magelona - Trochophora and Metatrochophora , shell Veliger overwhelm, was also confirmed in later studies; Heinrich Kühl (1973 and 1974) observed up to 12 blue mussel larvae in a Magelona -etatrochophora and mussel larvae as the only food in the intestines of a large number of examined Magelona larvae during investigations of Magelona in the mouths of the Elbe, Weser and Ems . Heinrich Kühl concluded from this that Magelona larvae "could destroy considerable amounts of mussel fry" and that the larvae "as food specialists are largely dependent on their main food in terms of location and time" and that their populations are therefore subject to fluctuations. Kevin Brett Johnson and Laura A. Brink (1998), on the other hand, investigated the question of whether plankton communities crammed together in plankton nets and vessels do not represent the predator-prey relationships under natural conditions. They simulated natural conditions with numerous plankton species and could not detect a single event in which a Magelona larva ate a mussel larva, which was probably due to the very rare encounters of these organism species under natural conditions.

Sample types

The first species described by Johann Friedrich Theodor Müller in 1858 on the basis of a find in Brazilian waters was the up to 17 cm long Magelona papillicornis . Magelona mirabilis ( Johnston , 1865) , Magelona minuta Eliason, 1962 , Magelona alleni Wilson, 1958 , Magelona filiformis Wilson, 1959 and Magelona johnstoni Fiege, Licher & Mackie, 2000 are particularly widespread in the North Sea .

Genera

The following two genera with around 67 described species belong to the Magelonidae family :

literature

Web links

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

Individual evidence

  1. ↑ Magelonidae Cunningham & Ramage, 1888. WoRMS , 2018. Retrieved November 7, 2018.