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Glaucus atlanticus – a kind of gastropod mollusks from the unit of nudibranchs. Nudibranch called a large group of marine gastropods. These animals are related to the usual snails and slugs, but at the same time, nudibranchs have a number of unique anatomical features. For this reason, they are isolated in a special unit, which has about a thousand species. The general principle of the structure of these animals is the same as at the garden snails, the basis of body is flat foot-sole, at the anterior end of which there are stalked outgrowths - one pair carries at its ends tiny eyes, and the second is the organ of smell. Olfactory outgrowths - rinofory - are relatively large, and they can both catch smell and taste. Nudibranch Glaucus, he's Glaukus or Glaucus atlanticus, or Glaucilla marginata is the only type of its kind. Glaucus Atlanticus - the common name of sea swallows, they're blue Glaucus, sea missiles or bullets.
The representatives of this species are characterized by a slender body, strongly stretched from the rear end. The head is short and slightly separated from the trunk. Wide, well-developed foot rounded in front and extends to the rear end of the body. The length of the body is 5-8 cm. On the sides perpendicular to the axis of the body there are three groups of cerate - finger-shaped outgrowths which receive branches of hepatopancreas (of the digestive gland). The length of cerate in each group varies considerably, with the longest one are located from the dorsal side. The presence of long cilia is considered as one of the mechanisms for increased buoyancy. Another adaptation of Glaucus atlanticus to retain at the water surface - the periodic ingestion of air bubble, then stored in the stomach of shellfish. Due to such placement of the gas bubble, the position of its body is in equilibrium state, in which the dorsal side faces down and the leg is adjacent to the surface of the water. The basic tone of the body is silver. The mouth tentacles, rinofory and the lower surface of cerate are painted by intense blue color. Dorsal side of different mollusks varies from dark blue to brown. The leg along the edge is framed by a blue stripe.
This kind of shellfish swims upside down and is kept at the surface of water. Special gas sacs located in the stomach help him to be there. Scientists are still debating whether Glaucus moves on its own initiative or, depending on the direction of wind and currents. These amazing creatures do not catch the eye of people except those days, when passing wind blows them into coastal waters, and even sometimes the waves throw them on the beaches.
Surprisingly, despite its inert life, Glaucus atlanticus are predators. They are fed by different drifting prey - coelenterates invertebrates. Glaucus prefers to hunt on other, larger pelagic organisms, even on the most poisonous representatives and dangerous to humans, such as the Portuguese “ships” and velella, on purple snail, etc. Sometimes some individuals become cannibals if they are given such opportunity. Due to its resistance to toxic nematocysts of Portuguese ships, mollusk fully digests it and retains the strongest poisons for its own use. Poison accumulates in his specialized sacs (cnidosacs), at the ends of the tentacles, thin cirrus "fingers". Since Glaucus accumulate poison, they can produce more powerful and deadly bites, compared with the Portuguese ship which they feed. But the most interesting food of Glaucus is velella or Istiophorus platypterus. These jellyfishes float on the surface like a small circular raft with a sail. Velella is a "gathering place" for several species of marine animals that travel on it in the ocean. The most "pragmatic" is good floating nudibranch Glaucus that not only travels on it, but also eats it. A hungry Glaucus, raking with tentacular outgrowths and holding on velella, pulls out and eats big chunks of its disk edge. Thus a jellyfish becomes not only a personal transport for Glaucus but also a part of dinner.
These nudibranch slugs spread throughout the world's oceans, mainly in temperate and tropical waters. Regions where they live include East and coasts of South Africa. It is possible to meet them in European waters, and on the east coast of Australia and Mozambique. Glaucus atlanticus don’t represent commercial value. They do not have permanent home, they spend all their life in perpetual motion in search of food. They move very slowly, so they are not removed far from the place of birth.
Glaucus atlanticus don’t have specific breeding season. Individual, in whose body matured sperm and eggs, finds the same fellow by smell. Glaucus - a hermaphrodite, i.e., contains both male and female reproductive organs, although unlike most nudibranchs, sea swallows mate with the ventral side. After mating, they lay eggs, but as they cannot leave them wherein at the bottom, or attach them to something solid, because they spend all their life attached to the surface of water, then they were forced to invent their own way of posterity rearing. The thread from linked eggs of Glaucus is enclosed within a thin tube of mucus, and in such form they are drifting in the ocean until the release of larvae.
He does not have a protective shell, but he does not need it, such bright coloration serves as a warning to predators that it is poisonous. The bright color perfectly disguises these animals on the background of corals, sponges and other fouling. Its body shape serves for masking, which skillfully imitates the substrate upon which the species occurs more often. In the case of threat shellfish can retract rinofory and gills, but even in case of damage these organs regenerate easily. Some species in case of danger can swim, however, in the water mollusks move not very quickly and not over short distances. However, despite all these tricks, some fishes and starfish still eat nudibranchs neglecting their virulence.
Way of feeding of large tropical doridacea from family of Phyllidiidae, also deprived of secondary dorsal gills is not typical even for shellfish. Phyllidiidae don’t have radula, but they are able to eat sponges, as well as their relatives, having radula. Instead of tearing off pieces of sponge by teeth, Phyllidiidae first partially "on the spot" treat portion of sponge by enzymes of salivary glands, and only then suck already half-digested food by muscular pharynx. Sponges secrete a variety of toxic substances. And Doridacea – sponge eaters, especially in the tropics, including those mentioned Phyllidiidae, use substances of eaten sponges for the subsequent synthesis of its own, also toxic to marine animals - predators, substances. Structure of radula’s teeth of Doridacea also depends on the food object. For example, Doridacea eating the sponges tend to have multiple rows of teeth, whereas the species that feed on bryozoans, for example, inhabiting the White and Barents seas Acanthodoris pilosa, as well as predators, the number of rows of teeth does not exceed 10-15. The rest of nudibranchs, on the contrary, tied their life with cnidarians (coelenterates) - soft corals, anemones, hydroids. These nudibranchs are already more similar to real predators than Doridacea. Nevertheless, many eolids also graze on fixed colonies of hydroid polyps. Here are just problems with their eating more - hydroids have burning stinging cells. Adaptation to eating of cnidarians arose not immediately. For example, species of the genus Tritonia have yet no special devices for storage of dangerous stinging cells - knidotsist. Probably in the mucus released by these mollusks, especially by glands of forefoot are contained substances isolating sensitive epithelium of the digestive tract from the burns of stinging cells. And the epithelium of nudibranchs is special. In various families of nudibranchs appear dorsal outgrowths - papillae, on top of which are accumulated living stinging cells of eaten polyps. The representatives of the family arminid instead of dorsal papillae on the sides of the body, special bubbles are formed, where also stinging cells are accumulated. In the tropical seas of this family is common genus Armina.
All, without exception, nudibranchs are hermaphrodites. The reproductive system of Nudibranchia is arranged very difficult, and is an important systematic feature. Fertilization of nudibranchs is internal, therefore representatives of many families have complex copulative apparatus, often bearing tubercles, spines or hooks, sometimes transforming into a complex system of stylets. In addition, there is always one or two special reservoir serving for storage of sperm obtained from a partner. Eggs are deposited in a special slimy cord, mostly spiral curled. Larva of nudibranchs - a veliger, of species with planktonic development has a larval shell, completely disappearing in the adult nudibranchs. The traditional system of nudibranchs includes 4 groups (suborder) - Doridacea are characterized by, in varying degrees, flattened body bearing dorsally semicircle of gills, Dendronotacea have usually branched outgrowths - secondary gills, Arminacea - elongated body without gills, dorsal spines and Aeolidacea - different number of unbranched outgrowths - -papillae bearing on top only special bag, where stinging cells obtained with food are accumulated. In the seas of Russia inhabit representatives of all major groups of nudibranchs.
If we look at this small, beautiful creature, we cannot say that it is a carnivore. Shellfish itself is not large 2 cm - 3 cm, but may be accessed from 5 cm to 8 cm in length. The interesting feature of Glaucus atlanticus is that he gets poison together with his food. So when he saw the victim, Glaucus atlanticus attacks it, and then eats. During the meal, shellfish sends by the branches of the digestive gland not shot stinging cells of their prey in special bags at the ends of cerates. Having got there the poison long retains its toxic properties, and G. atlanticus can use it for their own protection.
References
Adriana Morales. "What is the Glaucus atlanticus?" http://www.environmentalgraffiti.com/news-strange-yet-beautiful-sea-slug-glaucus-atlanticus
MacLellan, Amelia. “Glaucus atlanticus (blue sea slug).” Natural History Museum. The Natural History Museum [London]. 2011. 1 Jul. 2011. http://www.nhm.ac.uk/nature-online/species-of-the-day/collections/our-collections/glaucus-atlanticus/index.html
Scocchi, Carla and James B. Wood (Ed.). “Marine Invertebrates of Bermuda: Blue Ocean Slug (Glaucus atlanticus).” The Cephalopod Page. 1 Jul. 2011. http://www.thecephalopodpage.org/MarineInvertebrateZoology/Glaucusatlanticus.html
Van der Spoel, S., L. J. Newman, and K. W. Estep. “Pelagic Molluscs: Glaucus atlanticus.” Marine Species Identification Portal. 1 July. 2011.
http://species-identification.org/species.php?species_group=pelagic_molluscs&id=189
Schlesinger, Ami, Esti Kramarsky-Winter, and Yossi Loya. “Active Nematocyst Isolation Via Nudibranchs.” Marine Biotechnology: 11.4 (2009): 441-444.
“Feeding and Distribution.” Natural History Museum. The Natural History Museum [London]. 2011. 1 Jul. 2011.
http://www.nhm.ac.uk/nature-online/species-of-the-day/collections/our-collections/glaucus-atlanticus/distribution%20and%20ecology/index.html
