Thermosbaena mirabilis
| Thermosbaena mirabilis | ||||||||||||
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Thermosbaena mirabilis , pleon from anteriorly |
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| Systematics | ||||||||||||
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| Scientific name of the family | ||||||||||||
| Thermosbaenidae | ||||||||||||
| Monod , 1927 | ||||||||||||
| Scientific name of the genus | ||||||||||||
| Thermosbaena | ||||||||||||
| Monod , 1924 | ||||||||||||
| Scientific name of the species | ||||||||||||
| Thermosbaena mirabilis | ||||||||||||
| Monod , 1924 |
Thermosbaena mirabilis is a small stygobionte cancer from the order of the Thermosbaenacea, which is only known from a single site, a thermal spring in Tunisia. Like all Thermosbaenacea, it is considered a relic form whose ancestorslivedin the former Tethys Sea about 100 million years ago, and which only survived in underground waters with a few species.
description
Thermosbaena mirabilis reaches a body length of 3.2 millimeters (measured without antennas) and is whitish, translucent in color. The body is somewhat flattened dorsoventrally (from top to bottom). The short carapace reaches the second leg-bearing trunk segment. It is divided into two sections by a deep transverse furrow after the first quarter. A rostrum is not recognizable. The eyes are missing on the head, and the rudimentary scaly eye stalks still recognizable in some related genera have regressed. The first antennae carry two flagella on a three-segment stem (pedunculus), the main flagellum with ten to twelve, the minor flagellum with eight limbs. The pedunculus of the second antennae is five-membered, the single flagellum consists of six members. The trunk section ( peraeon ) consists of five limb-bearing segments. The legs (peraeopods) are typical two-branched split legs , the first pair of legs, the gnathopods, are designed differently, in the exopodite two limbs, base and ischium, are fused. The exopodite of the second to fourth pair of legs is two-segment, that of the fifth is only one-segment. On the pleon the first two segments have small extremities (pleopods), on the third to fifth they are absent. The sixth pleon segment is fused with the telson to form a pleotelson. Its extremities, the uropods , are two-branched split legs, the first of the two limbs of the exopodite is longer than the single-segment endopodite. Thermosbaena is the only representative of the Thermosbaenacea with only five pereiopods and one pleotelson and is therefore unmistakable.
Reproduction
Thermosbaena mirabilis is sexually separated. Sexually mature males swim around the habitat in search of females that they recognize upon direct contact. In the fertilized female, after a molt, the carapace forms a large, swollen brood pouch in which there is an egg sac with up to eight eggs on each side of the back. Pregnant females swim supine. The hatched young animals correspond in body shape to the sexually mature animals, so there are no larval stages.
distribution and habitat
The only locality of the species are the thermal springs of El Hamma in Tunisia. These have been used since Roman antiquity (in the seaside resort of Aquae Tacapitanae) until today. The species is the only species found here. It feeds mainly on detritus and cyanobacteria ("blue-green algae"), which occur here with the species Symploca thermalis , Spirulina labyrinthiformis , Oscillatoria terebriformis , Phormidium tenue and Phormidium papyraceum . The food is scraped off the hard surface with the mouthparts. The slightly salty and sulphurous thermal water has a temperature of 44.5 to 48 ° C. The species does not tolerate water temperatures above 50 ° C, but can survive at least several hours in water cooled to 30 ° C.
The species was discovered in the main spring Aīn el Bordj and the subsequent bathing pool. In later investigations, only a few animals were found here, and none in the basin. This is attributed to adverse effects from bathing, such as the use of soaps and shampoos. More animals were later discovered in a secondary spring, Aīn Baama, where they have so far been able to survive. Since the water quickly becomes very hot at greater depths, it is unclear whether the species can possibly also live in the groundwater in addition to the spring outlets.
A few million years ago in the late Pliocene , the area around the site was still part of the ocean floor. To this day there is a chain of temporarily water-bearing salt lakes in line with the springs, which trace the former coastline.
Research history
The species was discovered by Léon-Gaston Seurat in April 1923 and first described a year later by Théodore Monod . As a supposed intermediate form between the woodlice (Isopoda) and the hover shrimp (Mysida) and as one of the few colonists of thermal springs, it attracted a great deal of attention in the professional world, so that several biologists undertook research trips to El Hamma to find more animals. On the basis of the new material, Monod re-established the Thermosbaenacea order for the species in 1927.
Systematics
The species is taxonomically isolated, so that it is part of a monotypical family Thermosbaenidae. After the very similar construction of the mouthparts, the family Monodellidae is considered to be the closest related with the genera Monodella with one species (from Italy) and Tethysbaena with twelve species.
swell
- Hans-Eckhard Gruner: Class Crustacea. In: HE Gruner, M. Moritz, W. Dunger (editor): Textbook of special zoology (founded by Alfred Kaestner). Volume I: Invertebrates, Part 4 Arthropoda (without Insecta). 4th edition 1993. Gustav Fischer Verlag, Jena. ISBN 3-334-60404-7 .
- HP Wagner (1994): A monographic review of the Thermosbaenacea (Crustacea: Peracarida). Zoological Negotiations Leiden 291: 1-338.
- D. Jaume (2008): Global diversity of spelaeogriphaceans & thermosbaenaceans (Crustacea; Spelaeogriphacea & Thermosbaenacea) in freshwater. Hydrobiologia 595: 219-224. doi : 10.1007 / s10750-007-9017-1