Parasite rose
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Hermit crab with Calliactis sp. |
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Calliactis parasitica | ||||||||||||
| ( Couch , 1842) |
The parasite rose ( Calliactis parasitica ) belongs to the sea anemones and often lives in a mutualistic relationship with hermit crabs (Diogenidae) of different genera. It has a wide distribution area in the Mediterranean and the Atlantic at depths of up to 60 m. The species grows to a height of 8 cm and a diameter of 5 cm. It can settle itself on a snail shell through complex movements or is actively relocated to a snail shell by some hermit crab species. There it benefits from the leftover food left by the crab, while the crab is protected from predators such as octopuses by the nettle threads .
features
The first description of Calliactis parasitica was in 1842 by Couch under the name Actinia parasitica . There are many unofficially used species names, as the species was previously described by Linnaeus as Actinia effoeta (1767) or Sagartia effaeta . The wall sheet of the species is dark brown with lighter vertical stripes which can be reddish or greyish-brown in color. The not very long tentacles are slender and dirty light gray or rarely yellowish-orange in color. The number of tentacles can range up to about 700 pieces. The animal itself can reach a size of 80 × 50 mm. The white to purple nettle threads (acontia) are expelled by the cinclids even if they are only slightly irritated.
Distribution and occurrence
The species occurs on muddy-sandy soils at depths of up to 60 m and only rarely in the intertidal zone . It is often found on the shells of the whelk ( Buccinum undatum ), which are inhabited by hermit crabs such as Pagurus bernhardus , although several specimens can share a shell. Occasionally they can also be found on stones or empty cases. The species occurs in the Mediterranean, on the European Atlantic coast, the southwest coast of England and in western Ireland and can locally form very numerous populations.
Peculiarities of the way of life
The life of Calliactis parasitica is shaped by mutualistic relationships with hermit crabs.
nutrition
Calliactis parasitica is a non-selective, omnivorous organism. The food is therefore mainly composed of common representatives of the respective habitat and includes mollusks and crustaceans , which serve as food for hermit crabs. Individuals sitting on gastropod shells often curve their bodies so far that the mouth (peristome) is approximately parallel to the substrate and the tentacles touch the substrate. Food particles from the sediment as well as organisms from meio- and microfauna that were found in the gastrovascular system of the examined individuals are collected. Hermit crabs, which inhabit snail shells, also stir up the sediment while moving or, when plucking their prey, release food particles that get into the tentacles and are consumed.
Reproduction
Calliactis parasitica is segregated and lays eggs from May to August. A free-swimming planula larva develops from the eggs , which after a while settles on a substrate and undergoes a metamorphosis to become an adult animal.
Independent transfer to snail shells
The species Calliactis parasitica can attach itself independently to various substrates such as the housing of gastropods such as Buccinum undatum . Attachment is a remarkable process, during which the anemone first attaches itself to the housing with tentacles and the mouth . The foot disk is then removed and a tree-like movement is carried out. In the course of the movement, the oral attachment is loosened and the normal posture on the bowl is assumed. The anemone does not seem to distinguish between living and dead snails. Nor does it seem to matter whether the enclosure is inhabited by a hermit crab.
Detailed description of the transfer movement
Upon contact with a snail shell, some of the tentacles adhere to the surface and begin to weave in motion, followed by more tentacles. When the entire ring of tentacles adheres to the surface, the mouth field follows and the casing is held in place by partial contraction of the sphincter . The housing is often held so tightly that a resident hermit crab can hardly break free on its own. In the next step, peristaltic waves run down the animal's body towards the foot disk. A few minutes later, the foot disk becomes detached from the surface to which the animal is attached. Some of the specimens partially stick to the previous base due to the sticky deposits on the base disk and can only be completely freed from attachment and detachment after several cycles. The exact sequence of this detachment process can change considerably from time to time due to the position of the animal on the shell and the strength of the attachment to the base.
After detaching the foot disk from the base, the body of the anemone curves so that the foot disk is brought in the direction of the shell. In the course of this curvature, the foot disk under the cinclids increases significantly. These processes take between one and three minutes. Meanwhile, the mouth tentacles reposition themselves to make room for the foot disk. If the desired position is already occupied by another anemone, the animal decoys and bends again in another direction. This process, too, depends on the animal's position on the clamshell and is highly variable.
As soon as the first contact between the housing and the foot is established, the foot is slowly placed on the shell from this point and by further swelling of the basal region . This is followed by constant attaching, lifting and renewed attaching of the foot disk. This pinning usually takes between five and 15 minutes.
Finally, the attachment of the mouth disc and the tentacle ring is lifted and the anemone resumes its normal habit . Often the foot moves in the further course in the direction of the point where the tentacle wreath was attached previously.
Choice of populated shells
Free-standing specimens of Calliactis parasitica are more likely to adhere to housings than specimens that have attached themselves to a surface. They occupy shells of Buccinum species much more frequently than those of Pecten sp. or Mytilus sp. The attachment reaction is triggered by the housing itself and not by the resident. It is assumed that a previously unknown so-called shell factor triggers this reaction when it comes into contact with the periostracum of the snail. Highly stable and insoluble proteins or mucopolysaccharides are possible housing factors . Artificial replicas of the snail shells, shells with detached periostracum or with a plastic coating prevent or slow down attachment, while contact with detached periostracum triggers a strong attachment reaction.
Benefits of symbiosis for the hermit crab
While some hermit crabs such as Pagurus bernhardus show no particular behavior towards anemones sitting on their shells, some species, especially the genus Dardanus , actively settle on the anemones. In laboratory tests, it was observed that predators such as octopuses avoided hermit crabs with anemones on their shell, while they ate those without anemone throughout. Upon contact with the tentacle crown, the octopods showed a pain reaction and then avoided further contact with the cancer.
Individual evidence
- ↑ Calliactis parasitica (Couch, 1842) on WoRMS: http://www.marinespecies.org/aphia.php?p=taxdetails&id=100946 . Last access: December 23, 2018
- ↑ a b c d e R. Riedl (Ed.): Fauna and flora of the Mediterranean: A systematic marine guide for biologists and nature lovers . 3rd revised and expanded edition. Paul Parey, Hamburg / Berlin 1983, pp. 183-187, 193.
- ↑ a b c d e f J. P. Hayward, JS Ryland: Handbook of the Marine Fauna of North-West Europe . 2nd Edition. OUP, Oxford 2017, ISBN 978-0-19-854055-7 , p. 128.
- ↑ Chimtiroglou, C., Koukouras, A. (1991): Observations on the feedings habits of Calliactis parasitica (Couch, 1842), Anthozoa, Cnidaria . Oceanologica Acta 14 (4): 389-396.
- ↑ a b c DM Ross, L. Sutton, PB Medawar: The response of the sea anemone Calliactis parasitica to shells of the hermit crab Pagurus bernhardus . Royal Society Publishing: Series B. Biological Sciences, 1961, pp. 266-281.
- ↑ DM Ross: Protection of Hermit Crabs (Dardanus spp.) From Octopus by Commensal Sea Anemones (Calliactis spp.) . Nature 230, 1971, pp. 401-402.
