Aplysia depilans
Marbled sea hare ( Aplysia depilans )
The Marbled sea hare ( Aplysia depilans ) is a very large sea snail of the genus Aplysia from the order of opisthobranch ( Opisthobranchia ).
Features
The animals are up to 40 centimeters long and weighs up to 380 grams. Within the class of the screw, they are relatively very large animals. The body of Aplysia depilans is divided into head, neck and abdomen. The head has standing sideways in the throat area two, very moving tentacles with mechano- and chemoreceptors. They are usually clearly rolled in the longitudinal direction. Sitting paired rhinophores that can be extended from a lying under the skin pocket and pulled at risk between the head and neck. The rhinophores have at the top of notches with chemical sensors, they serve as olfactory sensory organ. Among the rhinophores are the eyes with simple lenses.
The neck widens to the abdomen. In this, the mantle cavity is reduced to the gills. In the back of the jacket sits at the back, the greatly reduced yellowish colored casing. This is relatively small (for the relatively large animal ) and measures just 1.5 centimeters. It is relatively flat and poorly calcified.
The lateral Parapodiallappen are very mobile and grown together at the back end. They are usually worn folded over the body; thus is formed over the body and a protective jacket height " Parapodialhöhle " which leaves only an opening for the water inlet and outlet for breathing.
At the rear end of the foot terminates in a wide hem. The animals move one hand by undulating movements of the foot away, like land snails. Very typical, however, is the movement by anchoring the outstretched front foot and dragging of the hind foot. These loopers -like locomotion is very typical for the genus lumpfish ( Aplysia ) as a whole. Aplysia depilans one of the seven species of the genus, one of which is known to occasionally swim. The swim is done by up-and -pounding and from front to back current wave-like movements of the Parapodiallappen.
The skin of the animals is colored dark brown to reddish brown. The color changes during life, but can not be matched to the substrate such as the ordinary octopus. Typical of Aplysia depilans are placed acting spot-like formations on the skin surface. These are white to light brown color. The edge of the Parapodiallappen is usually colored pink. There are also almost spotless copies, which you can then recognize only the dark skin color.
Geographic occurrence and habitat
Aplysia depilans is widespread in the eastern Atlantic from the British Isles to West Africa (Cape Verde, Senegal ) and in the Mediterranean. Aplysia depilans is a predominantly benthic living species, mostly in very shallow water of about 1.5 to 10 meters, but subtidal lives, as the maximum depth is 20 to 30 meters delivered. It occurs in sheltered, but also on stony, the surf of the Atlantic exposed coasts. Even in ports it was found. The actual tidal range ( Intertidal ) is usually avoided because of the risk of stranding here is relatively large. The animals can take no oxygen in the air and die after stranding relatively quickly. Occasionally animals are caught during low tide in tide pools and then come in flachstem water before ( often only a few tens of ores timer). On the Israeli coast Aplysia fasciata and Aplysia depilans occur together. There, it was observed that Aplysia depilans usually lives in a flatter, stronger wave-agitated water while Aplysia fasciata rather quieter areas preferred. Presumably this behavior is designed to avoid competition for food only where both types occur together.
Way of life
The animals feed primarily on species of the genus Ulva algae, particularly of sea lettuce ( Ulva lactuca ). The population sizes are strongly dependent on the availability of this food crop. Once the plants are grazed in a particular area, larger groups often migrate to new areas. You have an approximately one-year life cycle. During the mating season, the animals often gather in large groups. In the Mediterranean, this is the late summer, according to other, older sources, also from March to October. However, not all collections to be interpreted as mating aggregations ( which could explain the discrepancy in the figures). Aplysia depilans is a hybrid and has a hermaphroditic gland. Since it is not self-pollinating, it needs a partner. The fertilization occurs rarely mutually, but in reproductive chains with up to 30 animals or in closed rings with more than 20 animals. 20-30 After fertilization, the animals put long, jelly-like spawn cords from, where are the eggs. The several meters long spawning cords have a diameter of up just over one millimeter and usually yellow to pink - pink color. The number of eggs laid per animal can reach up to 3.3 million. In closely related species is even known that they can spawn several times, will also be larger then the number of eggs. At a temperature of 25 ° C, the Veligerlarven hatch after about 14 to 16 days. Brace yourself for weeks in free water, before they move on to the soil life. During the planktonic phase of life they eat single-celled phytoplankton. The mortality rate during the Veligerphase is very high. The duration of the planktonic phase is also dependent on a corresponding substrate, where they may metamorphose, usually subsequent food plant. After transition to the soil life they form around ( metamorphosis ) and see after about four to six days as small adult animals. You then begin to feed on sea lettuce. Although adult animals do not die directly after oviposition, however, show very soon after distinct signs of age, such as loss of weight, torn Parapodiallappen, loss of pigments and other and die soon thereafter. Very characteristic of this life cycle is that while almost six months, no larger specimens of Aplysia depilans be found.
Protection
The surface color and bright spots provide good camouflage against the rocky background. If the animals are irritated, they can emit a white or purple ink. Of Aplysia californica is known that the color depends on the diet.