Megascolecidae

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Megascolecidae
A giant earthworm of the genus Amynthas in China, Sai Kung, Hong Kong

A giant earthworm of the genus Amynthas in China, Sai Kung, Hong Kong

Systematics
Over trunk : Lophotrochozoa (Lophotrochozoa)
Trunk : Annelids (Annelida)
Class : Belt worms (Clitellata)
Subclass : Little bristle (Oligochaeta)
Order : Earthworms in the broader sense (Crassiclitellata)
Family : Megascolecidae
Scientific name
Megascolecidae
Rosa , 1891
Wet preparation of Aporodrilus ponga

The Megascolecidae (from the Greek μέγας mégas "large" and σκώληξ skṓlēx "worm") are a family of Crassiclitellata (earthworms in the broader sense) in the subclass of little bristles within the animal phylum of annelids (Annelida). In German they are also giant earthworms called (Engl. Giant earthworms ). But they are a different family than the Lumbricidae, which are usually referred to as earthworms in German . With over 1000 species , they are the most species-rich family of the Crassiclitellata.

features

The giant earthworms (Megascolecidae) have a cylindrical body with dorsal pores. As a rule there are four pairs of bristles on each segment , but in some genera such as Pheretima and Amynthas there are numerous bristles on each segment, the number of which is then often greater on the rear segments than on the front. The clitellum is ring-shaped or saddle-shaped and occupies up to 7 segments between the 12th and 18th segment. There is no pubertal tuberosity, but genital markings or porophores are generally present.

The giant earthworms have 1 to 3 gizzards in the area of ​​the esophagus , but only rarely (in pleinogaster ) one in the midgut . Intestinal blind sacs are sometimes present, and calcium glands are often present in the intestine. Within the closed blood vessel system , at least one supra-oesophageal blood vessel also runs in the front section of the animal in addition to the dorsal vessel over the esophagus. The nephridia are well (macronephridia) or only partially (meronephridia) developed.

Like all beltworms , the giant earthworms are hermaphrodites with mostly two pairs of testes in the 10th and 11th segment (holandric), otherwise a pair of testicles in the 10th (protandric) or 11th segment (metandric) and behind them a pair of ovaries in the 13th segment ( metagyn), which release their eggs into the open via an unpaired or a pair of female genital openings anterior to the 14th segment. The sperm conductors, on the other hand, cross several segments, including the ovary-bearing one, and the pair of male genital orifices is located behind the female abdomen on the 18th segment , in Nelloscolex and Tonoscolex on the 17th, rarely (with a few Pheretima species) on the 19th or 20th segment immediately behind the clitellum. The prostates , generally paired in the 18th segment, are grape-shaped without a central canal and usually open together with the sperm conductors through the male genital orifices, otherwise through prostate pores in the same segment as the male openings ( plutellus ) or further back ( nelloscolex and tonoscolex ). The receptacula seminis usually have blind sacs and open out in pairs or numerous openings in front of the testicle-bearing segments.

Habitat and adaptations

The Megascolecidae mostly live in the ground, but sometimes also on trees or bushes. Individual species are also found in fresh water and in the ocean.

Those species that live in dry soils show special physiological adaptations. For example, the nephridia (excretory organs) flow into the intestinal tract (so-called enteronephridia), which helps to save fluid. In the other annelid worms, the nephridia open directly outwards (metanephridia).

size

In Australia, the worms can grow to be over 2 meters long (in extreme cases allegedly about 3 meters) and more than a finger thick (extreme case about 3 centimeters), with a weight of up to 450 grams. They are also a tourist attraction there, to which an impressive field museum is dedicated ( Giant Earthworm Museum in Bass, 70 miles southeast of Melbourne). However, some species are also quite small.

Spread and threat

The Megascolecidae occur naturally in Australia, New Zealand, Africa, South and Southeast Asia (e.g. Japan) and America; the original distribution area seems to have been the southern hemisphere ( Gondwana ). Today, some of them are seriously threatened, especially in Australia, with the displacement by the introduced European earthworms probably being a main factor.

The only earthworm species that has been proven to be extinct through human action, the Lake Pedder earthworm , fell victim to a dam project.

Systematics

Both the relationship of the Megascolecidae to the other little bristles (Oligochaeta) and the relationships within the family are currently still controversial. Morphological and molecular genetic findings contradict one another in many places as a result of homoplasias .

Sample types

For individual species see:

Genera

Based on morphological delimitation, a distinction is currently made between around 34 genera , which together comprise over 1000 species :

literature

  • Reginald William Sims (1981): A classification and the distribution of earthworms, suborder Lumbricina (Haplotaxida: Oligochaeta). Bulletin of the British Museum (Natural History), Zoology Series 39 (2), pp. 103–124, here p. 112.
  • Reginald William Sims, Brian M. Gerard: Earthworms: Keys and Notes for the Identification and Study of the Species. Doris M. Kermack, RSK Barnes (Ed.): Synopses of the British Fauna (New Series), No. 31. EJ Brill, London 1985. p. 126.

Web links

Commons : Megascolecidae  - collection of images, videos, and audio files

Individual evidence

  1. ↑ Hypolimnus pedderensis: IUCN Red List of Threatened Species.
  2. ↑ Jamieson, BGM, Tillier, S., Tillier, A., Justine, J.-L., Ling, E., James, S., McDonald, K., Hugall, AF (2002): Phylogeny of the Megascolecidae and Crassiclitellata (Annelida, Oligochaeta): combined versus partitioned analysis using nuclear (28S) and mitochondrial (12S, 16S) rDNA. Zoosystema 24: 707-734.
  3. ↑ a b B. GM Jamieson: The australian earthworm genus Spenceriella and description of two new genera (Megascolecidae: Oligochaeta) . In: Memoirs of the National Museum of Victoria . 33, 1972, pp. 73-87.