Parergodrilidae
| Parergodrilidae | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Parergodrilidae | ||||||||||||
| Reisinger , 1925 |
Parergodrilidae is the name of a family with two species of very small polychaeta (polychaeta) that live in the sand gap system of the oceans or in leaf litter and feed on bacteria . Parergodrilus heideri is the only species of truly land-dwelling annelid worms that does not belong to the belt worms .
features
The Parergodrilidae have a very small, maggot-shaped body with only a few similar segments that lack any parapodia, with a rounded prostomium and a peristomium formed as a ring , on which neither antennae nor palps sit. A pair of retractable nuchal organs are present in Stygocapitella , but absent in Parergodrilus . The body surface is covered with sensory papillae. A muscular throat membrane is absent, but the segmental septum behind the head is the only fully developed one, while the rest are almost entirely absent. The simple bristles sit in paired ventrolateral bundles and are capillary- shaped or forked in Stygocapitella, but spines in Parergodrilus . There are no cirrus at the pygidium. At the eversible, abdominal side sitting pharynx a close esophagus , stomach, midgut and rectal on; in Stygocapitella the intestine is spiral-shaped. In Stygocapitella , the metanephridia are distributed over the entire body, whereas in Parergodrilus they are limited to a few segments. The closed blood vessel system in Parergodrilus lacks a central heart, while in Stygocapitella a heart apparently lies at the level of the esophagus. The autapomorphy of the group is the unique arrangement of the muscle and glandular cells of the pharynx, which I distinguish in the shape of the tongue and in the fact that there is a muscle bulb in Stygocapitella , while it is absent in Parergodrilus . The tongue can be turned out and serves to graze food particles from the substrate.
A strong cuticle spans the weak body muscles from a network of ring-shaped and longitudinal muscle fibers . Stygocapitella moves by hooking its front end around grains of sand, pulling the body forward through muscle contraction, and then stretching the back of the body.
Development cycle
The Parergodrilidae are separate sexes. In the male of Stygocapitella , a sperm sac with two testes leads to a pair of sperm conductors that open out through glandular pores on the ventral side of the 10th segment. The female of Stygocapitella has an ovarian sac with two ovaries that lead to the outside via a pair of fallopian tubes through pores on the abdomen between the 10th and 11th segment. Part of the fallopian tube serves as the receptaculum seminis ; so there is copulation and internal fertilization. Stygocapitella lays large, yolk- rich eggs that are fastened in a gelatinous shell between grains of sand. Creeping worms with 4 bristle-bearing segments hatch from the eggs without any intermediate stage.
The two species and their distribution
Two species (each in a monotypic genus) in the family are known:
- Parergodrilus heideri is common all over Europe. Here it lives in thick, wet layers of decaying leaf litter and in rotten stumps in beech forests , occasionally also in and next to streams and ponds, where it feeds on the bacterial flora of the decaying plant parts.
- Stygocapitella subterranea has been found in sand gap systems on the shores of the northeastern Pacific Ocean , the northern Atlantic Ocean , the North Sea , the Mediterranean , the Black Sea , the Augusta River, and the Margaret River in Western Australia, as well as on coarse sandy beaches in New Zealand . It is possible that there are numerous cryptospecies , especially since, due to the direct development without a pelagic larval stage, there is no rapid spread.
Systematics
Erich Reisinger established the family in 1925 on the basis of the terrestrial and limnic genus Parergodrilus found in Austria . In a work from 1960 he once again emphasizes the decisive similarities between the two genera or species, with which he justifies the assignment of Stygocapitella to this family. Due to their supposedly original, very simple building plan, the family was long counted among the Archiannelida that are no longer recognized as a natural group . Based on their phylogenetic examinations, Struck, Golombek and others added the family to the Orbiniida in 2015 .
literature
- Erich Reisinger 1925: A rural archiannelide. At the same time a contribution to the systematics of the Archiannelids. Journal for Morphology and Ecology of Animals 3 (2/3), pp. 197-254. doi: 10.1007 / BF00408145
- Stanley J. Edmonds: Fauna of Australia, Volume 4A. Polychaetes & Allies. The Southern Synthesis 4. Commonwealth of Australia, 2000. Class Polychaeta. Pp. 322f., Family Parergodrilidae.
- Torsten Hugo Struck, Anja Golombek, Anne Weigert, Franziska Anni Franke, Wilfried Westheide, Günter Purschke, Christoph Bleidorn, Kenneth Michael Halanych (2015): The Evolution of Annelids Reveals Two Adaptive Routes to the Interstitial Realm Current Biology. Current Biology 25 (15), pp. 1993-1999. DOI: 10.1016 / j.cub.2015.06.007
- Anne Weigert, Christoph Bleidorn (2016), Current status of annelid phylogeny. Organisms Diversity and Evolution 16 (2), pp. 345-362. DOI: 10.1007 / s13127-016-0265-7