Chaetogaster

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Chaetogaster
Chaetogaster limnaei

Chaetogaster limnaei

Systematics
Trunk : Annelids (Annelida)
Class : Belt worms (Clitellata)
Order : Little bristle (Oligochaeta)
Family : Naididae
Subfamily : Naidinae
Genre : Chaetogaster
Scientific name
Chaetogaster
from Baer , 1827

The genus Chaetogaster (Greek χαίτη chaítē " bristle ", γαστήρ gastḗr "belly": "bristle belly") belongs to the annelid worms (Annelida). It belongs to the Naididae family from the order of the little bristle (Oligochaeta); within the Naididae it belongs to the subfamily of the Naidinae . They are about 2–25 mm long, transparent aquatic worms, some of which form conspicuous animal chains as a result of asexual reproduction and are common in freshwater.

morphology

Outwardly, the animals correspond to the general blueprint of the Naidinae, but in contrast to the other species have their setae (bristles) only on the belly side (hence the name). The size of the animals and the setae is quite variable even within individual species.

Occurrence and nutrition

Although the animals mainly occur in standing or flowing fresh water, the largest species, Chaetogaster diaphanus , also lives in brackish water. All species seem to be very widespread within Europe and are also often found on several continents.

The animals generally appear quite lively, but they cannot swim in a targeted manner. They therefore live on solid ground (on plants, on stones, a subspecies also on snails). They feed by sucking in small organisms of suitable size. The food composition differs between the species, since the different body size also leads to different food components absorbed. While the largest species, Ch. Diaphanus, consumes organisms in the order of about 0.3 - 3 mm in length, which are mostly small animals ( rotifers , cladoceras, etc.), preferably about Ch. Limnaei organisms in the order of magnitude of around 0.03 - 0 , 3 mm, which are predominantly algae ( diatoms and green algae) or very small animal organisms. Basically, the species are omnivorous, but the larger ones mainly eat animal food, the smaller mostly vegetable particles. How unselectively food is consumed is also shown by the fact that grains of sand or other practically indigestible particles (e.g. conifer pollen) are repeatedly found in the stomach, which are also in the specified size range.

Physiologically, Chaetogaster species have long been known to have an acidic gastric reaction similar to that of vertebrates.

The special case of Chaetogaster limnaei

Lymnaea stagnalis and Chaetogaster limnaei limnaei

A specialty is the species Ch. Limnaei , which occurs in two "subspecies" that differ significantly in their way of life. One subspecies feeds parasitically inside snails ( Ch. L. Vaughini ) and only attacks snails above a certain minimum size. It apparently feeds mainly on kidney cells from the host snail. The other subspecies ( Ch. L. Limnaei ) attaches to the outside of the snail (e.g. of the genera Lymnaea , Physa , Ancylus or Australorbis ) on the soft body and to the inside of the shell and can move freely there (so-called. Epökie ). It consumes various small organisms that it can catch from its host by sucking it in. In addition to z. As rotifers and algae also Cerkarien and miracidia (larvae of flukes count) to their food. The ecological connection between this biological control of parasites has been examined on various occasions. It seems to vary in strength, but it obviously cannot be applied in practice. Sometimes the subspecies Ch. L. limnaei also found on freshwater mussels, particularly on the genus Sphaerium .

Reproduction

Like practically all representatives of the Naidinae, the species of the genus Chaeogaster are characterized by a multiple asexual reproduction . Characteristic is the formation of two or more animals in the form of animal chains, which arise in the manner of a sprout . By dividing (paratomy) these animal chains, new individuals can arise in an asexual way, which genetically represent an identical image of the mother animal. However, in between (especially in late summer / autumn) normal bisexual reproduction often occurs. The subspecies Ch. L. limnaei leaves its host (the snail) in late summer / autumn, moves on to free life in the water and infects new snail individuals in spring.

Systematics

The affiliation of the genus Chaetogaster to the family of Tubificidae and to the subfamily of Naidinae is now valid not only through morphological but also molecular genetic findings. According to cytochrome oxidase I sequence studies, the closest relationship seems to be to the genus Amphichaeta (cf. Naidinae ).

The genus Chaetogaster Baer 1827 is currently divided into nine valid (i.e. nomenclaturally valid) species:

Individual evidence

  1. ↑ Streit, B .: Morphometric relationships and feeding habits of two species of Chaetogaster , Ch. Limnaei and Ch. Diastrophus (Oligochaeta). Arch. Hydrobiol./Supp. 48, pp. 424-437, 1977
  2. ↑ Gruffydd, LD (1965): Evidence for the existence of a new subspecies of Chaetogaster limnaei (Oligochaeta) in Britain. J. Zool. 146: 175-196.
  3. ↑ Buse, A. (1974): The relationship of Chaetogaster limnaei (Oligochaeta: Naididae) with a variety of gastropod species. J. Anim. Ecology 43: 821-837.
  4. ↑ Michelson, EH (1964): The protective action of Chaetogaster limnaei on snails exposed to Schistosoma mansoni . The Journal of Parasitology 50: 441-444.
  5. ↑ Rodgers, JK, Sandland, GJ, Joyce, SR, Minchella, DJ (2005): Multi-species interactions among a commensal ( Chaetogaster limnaei limnaei ), a parasite ( Schistosoma mansoni ), and an aquatic snail host ( Biomphalaria glabrata ). Journal of Parasitology 91: 709-712.
  6. ↑ Barbour, MT (1977): Chaetogaster limnaei limnaei (Oligochaeta: Naididae) inhabiting the mantle cavity of the pill clam Sphaerium . Transactions of the American Microscopical Society 96: 141-142.
  7. ↑ Streit, B. (1974): Population dynamics of Chaetogaster limnaei limnaei in a population of Ancylus fluviatilis . Arch. Hydrobiol./Supp. 47: 106-118.
  8. ↑ Sjölin, E., Christer Erséus, M. Källersjö: Phylogeny of Tubificidae (Annelida, Clitellata) based on mitochondrial and nuclear sequence data. Mol. Phyl. Evol. 35, pages 431-441, 2004
  9. ^ Bely, AE, Wray, GA: Molecular phylogeny of naidid worms (Annelida: Clitellata) based on cytochrome oxidase I. Mol. Phyl. Evol. 2004, pages 50-63, 2003