Marbled sea hare
| Marbled sea hare | ||||||||||||
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Marbled sea hare ( Aplysia depilans ) |
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| Scientific name | ||||||||||||
| Aplysia depilans | ||||||||||||
| JF Gmelin , 1791 |
The marbled sea hare ( Aplysia depilans ) is a very large sea snail of the genus Aplysia from the order of the hind gill snails (Opisthobranchia).
features
The animals grow up to 40 centimeters long and weigh up to 380 grams. Within the class of snails, they are relatively very large animals. The body of Aplysia depilans is divided into the head, neck and abdomen. The head has two sideways, very mobile tentacles with mechano and chemoreceptors in the area of the throat. They are usually clearly curled in the longitudinal direction. Paired rhinophores sit between the head and neck, which can be extended from a pocket under the skin and retracted in case of danger. The rhinophores have notches at the top with chemosensors, they serve as an olfactory sensory organ. Under the rhinophores are the eyes with simple lenses.
The neck widens towards the abdomen. In this is the reduced mantle cavity with the gills. In the rear part of the jacket sits the strongly reduced yellowish colored case on the back. This is relatively small (for the relatively large animal) and measures only about 1.5 centimeters. It is relatively flat and only weakly calcified.
The lateral parapodial lobes are very mobile and have grown together at the rear end. They are usually worn folded over the body; This creates a protective “parapodial cavity” over the body and mantle cavity, leaving only one opening for water to enter and exit for breathing.
At the rear end the foot ends in a wide hem. On the one hand, the animals move by wave-like movements of the foot, similar to land snails. Very typical, however, is locomotion by anchoring the forward-stretched front foot and pulling the back foot. This caterpillar-like locomotion is very typical of the sea hares ( Aplysia ) genus as a whole. Aplysia depilans is one of the seven species in the genus that are known to occasionally swim. Swimming is done by striking up and down and wave-like movements of the parapodial lobes from front to back.
The skin of the animals is dark brown to reddish brown in color. The color changes during life, but cannot be adapted to the subsurface, as is the case with the common octopus . Typical of Aplysia depilans are patchy appearing spots on the skin surface. These are from white to light brown in color. The edge of the parapodial lobes is usually pink in color. But there are also almost spotless specimens that can only be recognized by their dark skin color.
Geographical occurrence and habitat
Aplysia depilans is widespread in the Eastern Atlantic from the British Isles to West Africa ( Cape Verde Islands , Senegal ) and in the Mediterranean. Aplysia depilans is a predominantly benthic species that lives mostly in very shallow water of around 1.5 to 10 meters, but is subtle, with a maximum depth of 20 to 30 meters. It occurs on protected, but also on stony coasts exposed to the surf of the Atlantic. She was also found in ports. The actual tidal area (intertidal) is usually avoided, as the risk of stranding is relatively high here. The animals cannot take in oxygen from the air and die relatively quickly after being stranded. Occasionally, animals are caught in tide pools during low tide and then appear in shallow water (often only a few tens of centimeters). Aplysia fasciata and Aplysia depilans occur together on the Israeli coast . It was observed there that Aplysia depilans mostly lives in shallower, more wavy water, while Aplysia fasciata prefers quieter areas. Presumably, this behavior to avoid food competition is only developed where both species occur together.
Way of life
The animals feed primarily on species of the algae genus Ulva , especially sea lettuce ( Ulva lactuca ). The population sizes are heavily dependent on the availability of this food crop. Once the plants have grazed in a certain area, larger groups can often migrate to new areas. They have a life cycle of around one year. During the mating season, the animals often gather in large groups. In the Mediterranean it is late summer, according to other, older sources also from March to October. However, not all accumulations are to be interpreted as mating accumulations (which could explain the discrepancy in the information). Aplysia depilans is a hermaphrodite and has a hermaphrodite . Since she is not self-fertilizing, she will need a partner. However, fertilization rarely takes place alternately, but in reproductive chains with up to 30 animals or in closed rings with z. T. over 20 to 30 animals. After fertilization, the animals put down long, jelly-like spawning lines in which the eggs are located. The spawning lines, which are several meters long, have a diameter of just over a millimeter and are usually yellow to pinkish-pink in color. The number of eggs laid per animal can reach up to 3.3 million. It is even known that closely related species can spawn several times, and the number of eggs then increases accordingly. At a temperature of 25 ° C, the Veliger larvae hatch after about 14 to 16 days. They stay in open water for weeks before moving on to soil life. During the planktonic life phase they eat unicellular phytoplankton . Mortality during the Veliger phase is very high. The duration of the planktonic phase also depends on a corresponding substrate where they can metamorphose, usually the later food plant. After transition to soil life, they transform ( metamorphosis ) and look like small adult animals after about four to six days. They then start to eat sea lettuce. The adult animals do not die immediately after laying their eggs, but very soon afterwards they show clear signs of aging, such as loss of weight, torn parapodial lobes, loss of pigments and other things, and then die quite soon afterwards. It is very characteristic of this life cycle that no larger specimens of Aplysia depilans are found for almost six months .
protection
The surface color and light spots provide good camouflage against the stony background. When the animals are irritated, they may expel white or purple ink. It is known of Aplysia californica that the color depends on the food.
swell
Individual evidence
- ↑ a b c d e f Thomas H. Carefoot: Aplysia: Its Biologie and Ecology. In: Oceanography and Marine Biology. 25, London 1987, pp. 67-284.
- ↑ See for example Aplysia depilans on conchology.be (English)
- ↑ See for example Aplysia depilans from Portugal in the Sea Slug Forum (English).
- ^ TG Nolen, PM Johnson, CE Kicklighter, T. Capo: Ink secretion by the marine snail Aplysia californica enhances its ability to escape from a natural predator. In: Journal of Comparative Physiology A (Neuroethology, Sensory, Neural, and Behavioral Physiology). 176, No. 2, 1995, pp. 239-254, doi : 10.1007 / BF00239926
literature
- Thomas H. Carefoot: Aplysia: Its Biologie and Ecology. In: Oceanography and Marine Biology. 25, London 1987, ISSN 0078-3218 , pp. 67-284, ( Google Books ).
