Biwadrilus bathybates

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Biwadrilus bathybates
Systematics
Class : Belt worms (Clitellata)
Subclass : Little bristle (Oligochaeta)
Order : Earthworms in the broader sense (Crassiclitellata)
Family : Criodrilidae
Genre : Biwadrilus
Type : Biwadrilus bathybates
Scientific name of the  genus
Biwadrilus
Jamieson , 1971
Scientific name of the  species
Biwadrilus bathybates
( J. Stephenson , 1917)

Biwadrilus bathybates (currently again Criodrilus bathybates ) is the name of the mud in freshwater encountered oligochaetes - kind from the family of Criodrilidae in order Crassiclitellata (earthworms in the broader sense), originally from the Lake Biwa in Japan is known, but was also found in other inland waters of Japan. It is the only recognized species of the monotypical genus Biwadrilus , which was temporarily also considered a separate family Biwadrilidae .

features

Biwadrilus bathybates has a square body without dorsal pores, but with a particularly pronounced dorsal groove at the back and is around 15 to 30 cm long and 3 to 4 mm wide with a number of around 200 to 250 segments, at the point of the male genital openings on the 13th But segment over 5 mm wide. The prostomium of Biwadrilus bathybates is zygolobic, so it lies against the peristomium without a dorsal process. There are four pairs of bristles per segment on the four edges of the body . The animal is unpigmented so that the blood vessels and the intestinal contents are visible at least outside the clitellum. The annelid worm is very soft and breaks down quickly in the air.

The intestinal canal of Biwadrilus bathybates has neither gizzards nor calcified glands, typhlosolis or blind sacs. The closed blood vessel system has three longitudinal vessels , namely a dorsal vessel, a supra-oesophageal vessel and an abdominal vessel, but no neural vessel. In the 5th and 6th segment the longitudinal vessels are connected by small commissures, in the 7th to 11th segment by paired lateral hearts . Internal organs and skin are well supplied with blood through fine capillary networks, especially in the tail area, where the gas exchange takes place via the capillary-rich skin. The large nephridia are well developed, but are absent in the first 13 segments.

The ring-shaped clitellum of the hermaphrodite occupies all or most of the segments from the 16th to the 34th segment and has no pubertal tuberosity . The two pairs of (Holandrian) iridescent testicles are located in the 10th and 11th segment and sperm sacs in the 9th and 12th segment. The paired ovaries in the 13th segment are fan-shaped with funnels and produce low-yolk eggs; the paired Eisacke are in the 14th segment. The pair of female genital orifices is on the 14th segment, the pair of male genital orifices in deep slits on large, protruding porophores on the 13th segment and thus - unlike most of the Crassiclitellata - in front of the female. The prostates open out through the male genital orifices. Receptacula seminis are absent; instead, the sperm are transferred via sac-shaped pseudospermatophores .

distribution

Biwadrilus bathybates is native to Japanese inland waters only. It is originally known from Lake Biwa in south-central Honshu in Japan and was initially thought to be an endemic species there. The species described as Criodrilus miyashitai from the Yura River in Komorimachi near Kyoto and from irrigation canals for rice fields near Tsuruoka in Yamagata-ken is a synonym .

Habitat and way of life

Biwadrilus bathybates is found in the mud of inland waterways such as lakes and slow-flowing rivers and canals, where it burrows through the ground. Since the mud is usually poor in oxygen, the annelworm holds its highly perfused, tightly capillary tail part out of the ground into the open water for most of the time in order to be able to take up oxygen and release carbon dioxide.

Like other Crassiclitellates , Biwadrilus bathybates is a substrate eater, which digests the organic components of the swallowed substrate such as the microorganisms and plant residues contained therein.

Development cycle

Like all belt worms , Biwadrilus bathybates is a hermaphrodite , in which two individuals mate with each other. For this purpose, the sack-shaped pseudospermatophores are attached to the sex partner, while there are no receptacula seminis. With the help of mucus deposits from the extensive clitellum , elongated egg cocoons that are tapered on both sides are formed, in which the numerous fertilized, low-yolk eggs are laid. The embryos develop into small, young worms in the cocoons.

System of the genus and species

Biwadrilus bathybates is one of currently three recognized species of the family Criodrilidae , which in turn belong to the order Crassiclitellata , the earthworms in the broader sense.

In 1917 John Stephenson described the species Criodrilus bathybates in the family Criodrilidae on the basis of finds from Lake Biwa . In 1971 Barrie GM Jamieson granted this species its own genus, named it Biwadrilus bathybates and placed it in its own family Biwadrilidae ( Biwadrilus "Biwa earthworm", after Lake Biwa and ancient Greek δρίλος, δρῖλος drílos, drîlos "earthworm" ).

RJ Blakemore introduced Biwadrilus bathybates back into the family Criodrilidae based on a study from 2006. Found in Japanese rivers and irrigation canals, the species Criodrilus miyashitai Nagase & Nomura, 1937 was recognized as a synonym of Biwadrilus bathybates .

literature