Giant lobsters

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Giant lobsters
Riesenassel ♂ (Bathynomus giganteus)

Riesenassel ♂ ( Bathynomus giganteus )

Systematics
Subclass : Eumalacostraca
Superordinate : Satchel Shrimp (Peracarida)
Order : Woodlice (isopoda)
Subordination : Flabellifera
Family : Cirolanidae
Genre : Giant lobsters
Scientific name
Bathynomus
Milne-Edwards , 1879
Prepared specimen of Bathynomus richeri .

The giant isopods ( Bathynomus ) are a genus within the order of the woodlice . They are believed to be found in large numbers on the seabed of the Atlantic and Pacific Oceans .

The French zoologist Alphonse Milne-Edwards described these animals for the first time in 1879 after he had fished a young male of B. giganteus from the Gulf of Mexico . At the time, the discovery was a sensation, because only recently had Charles Wyville Thomson shaken the general assumption that there was no life in the depths of the world's oceans through his work. The first female specimen could not be caught until 1891.

description

With a length of up to 45 cm and a weight of up to 1.7 kg, giant isopods are a good example of deep-sea gigantism , because most of their relatives are between one and five centimeters in length. Nevertheless, their morphology is similar to that of the landlice : their bodies are compressed dorso-ventrally and protected by a calcareous exoskeleton consisting of scale-shaped segments . The first of these segments is fused with the head, often the last segments are fused with each other and thus form a “tail armor” over the shortened abdomen ( pleon ).

In cave and deep-sea dwellers, the eyes are usually reduced or gone, and the species in question rely on other senses. Giant isopods, on the other hand, have enormously enlarged eyes in order to be able to see sufficiently despite the weak lighting. Depending on the size of the animal, they consist of 3,000–4,000 facets . The eyes are very sensitive to light and are permanently and severely damaged when normal daylight hits them.

The giant isopods have two pairs of antennas . The first antenna is very short and, unlike most other isopods, has a short secondary whip. The chest legs are arranged in seven pairs. In addition, there is a pair of maxillipedas, i.e. walking legs that have been transformed into mouthparts through evolution. The abdomen consists of five segments, each equipped with a pair of leaf legs ( pleopods ) that are formed into flat plates , which are used for swimming and as gills . They also have additional tuft gills on the first and second pleopods.

The woodlice are pale purple in color.

Way of life and foraging

Giant isopods are foragers in deep sea benthos . They occur in the sublittoral to the bathypelagial zone at depths from 150 m to over 2,000 m and are solitary. They prefer muddy and clayey soils. Although they are omnivores, they mainly feed on dead whales , fish, and octopuses . But they may also hunt slow representatives of the echinoderms such as sea ​​cucumbers as well as sponges , radiant animals , roundworms and maybe even fish. It has been observed that they attack the catch in bottom trawls . Due to the fluctuating feeding conditions on the deep sea floor, giant isopods are well adapted to long-term food shortages; in aquariums they have survived for up to eight weeks without food. If they come across a rich supply of food, they will eat so much that they can hardly move.

Reproduction

Studies of the seasonal amount of giant isopods suggest a higher reproductive capacity in the spring and winter months . This is probably due to the lack of food during the summer. Sexually active adult females form a brood sac ( marsupium ) by overlapping the brood plates of their swimming legs. The fertilized eggs , the largest of the marine invertebrates, remain in this incubator for an unknown time. If the female eats too much, she runs the risk of losing the brood due to the increase in body size.

The young woodlice leave the protection of the brood pouch as almost fully developed miniature versions of the adults, also called manca . The only thing missing is the last pair of swimming legs.

species

Bathynomus doederleinii

A distinction is made between nine types of giant isopods:

Giant lobsters in literature and the media

  • The novel Meteor (2003) by the American author Dan Brown deals with the discovery of fossils of a Bathynomus species on an alleged meteor.
  • In January 2018, giant isopods were distributed as memes on the reddit site under the English name "Isopod".

Individual evidence

  1. ↑ a b c M. Moritz, W. Dunger: Textbook of Special Zoology, Volume I: Invertebrates, Part 4: Arthropoda (without Insecta) . Ed .: Hans Ekkehard Gruner. 1993, ISBN 3-334-60404-7 , pp. 439-486 .
  2. ↑ Dr. Steven C. Chamberlain, V. Benno Meyer-Rochow, William P. Dossert: Morphology of the compound eye of the giant deep-sea isopod Bathynomus giganteus . In: Journal of Morphology . tape 189 , no. 2 , 1986, p. 145-156 , doi : 10.1002 / jmor.1051890205 .
  3. ↑ P. Briones-Fourzan, E. Lozano-Alvarez, A. Milne Edwards: Aspects of the biology of the giant isopod Bathynomus giganteus (1879) (Flabellifera: Cirolanidae), off the Yucatan Peninsula . In: Journal of crustacean biology . tape 11 , no. 3 , 1991, ISSN  0278-0372 , pp. 375-385 .

literature

Web links

Commons : Giant Asseln ( Bathynomus )  - Collection of images, videos and audio files