Crab found in all the oceans of the world. There is also a freshwater and terrestrial crabs, particularly in tropical regions. Crab is a crab that live in marine waters and rarely rises to the beach, while the crab is a crab inhabitants of freshwater (rivers and lakes).
Crabs vary in size from the pea crab, a width of only a few millimeters, up to the Japanese spider crab, with a leg span of up to 4 m.
Anatomy.
True crabs have five pairs of legs; The first pair of legs is modified into a pair of claws and are not used to moving. In almost all kinds of crabs, except a few (eg, Raninoida), belly folded under the cephalothorax. Part crab mouth covered by maxilliped flat, and the front of the carapace does not form a long rostrum. Gills crabs are formed of flattened plates ( "phyllobranchiate"), similar to the gills of shrimp, but with a different structure.Crab.
Yuyu is a kind of freshwater crab. The word is taken from the Java language. This freshwater crabs there are many kinds, and is often found in rivers, lakes and paddy fields; included in the trenches and muddy soil in the vicinity. In zoology, the types of crab are usually classified into Parathelphusidae tribe or Gecarcinucidae, superfamilia Gecarcinucoidea. Yuyu not rarely seen outside of the water. Unlike the sea crabs that a pair of flat-shaped hind legs, crab legs all have a pointed tip. Shell crab backs generally brownish, blackish to dark purple; often have indentations like former hooves trampled. Edge of the shell sometimes there who have some small spines.Animal pests.
Some types of crab is a pest to farmers because it makes nest holes in the rice fields and the edge of the irrigation channels, and the leaking of water needed to irrigate the fields. Certain types of rice seedlings were also damaged, as well as Parathelphusa convexa, Bogoriensis P., and P. tridentata. Type Terrathelphusa (Perbrinckia) kuhli recorded once damaging the young tobacco plants in total in Banyumas.Predators.
Yuyu many predators. Beavers, mice, lizards, and various species of water birds listed as natural enemies, which are crucial for controlling the crab population. In the area of brackish water, frogs (Fejervarya cancrivora) and mangrove snake (Fordonia leucobalia) are known to prey on crab. Java Farmers often use animal meat as bait for rat poison fields.Know Some crab species Toxic.
Talk about the crab, usually we will refer to the crabs that can be consumed, such as mud crab (Scylla spp.) Or crab (Portunus pelagicus). However, the real world is a lot of species of crab, both the crabs from the group brachyura or Anomura. Brachyura is a group of true crabs, have four pairs of legs motion fully developed, while Anomura is a group of crabs 'false', only has three pairs of legs fully developed motion - the fourth leg motion is very small or hardly visible.Of all the species now known, in fact only a few that can be consumed. In fact, some species of crabs are known as the toxic species. Then, the question that then arises is, what is poisonous crab? Any toxic contained in the body of the crab? Furthermore, why the crabs become toxic? Let's look together the intricacies of toxins in crabs.
Toxins in the body of the crab.
Several types of known poisons contained in the body of the crab is domoic acid, Okadaic acid, Palytoxin, tetrodotoxin, saxitoxin, neosaxitoxin, surugatoxin, brevetoxin, nereistoxin, and gonyautoxin. Besides Palytoxin, all toxins are included in the group of neurotoxins, which is toxic to nerve cells in action, and usually interact with membrane proteins.Domoic acid is a toxic acidic. The name 'domoic' comes from the word 'doumoi', the local term Japanese from red algae Chondria armata. According to Horner (published in 1996), these toxins are known to accumulate in tissues of crabs and shellfish.
Okadaic acid has a way of working that is similar to domoic acid. Okadaic term taken from the marine sponge Halichondria okadai. However, producing this toxin that is actually a group of dinoflagellate algae. Nevertheless, it turns out this toxin can also be contained in the body of the crab.
Palytoxin first known there are fish that consume zoanthids Palythoa, anemone-like organisms. Palitoksin works by forming a new membrane channels that exceed normal that ion transport becomes uncontrolled and cause malfunction of cells and tissues.
Tetrodotoxin (TTX) was first detected in fish Tetraodontidae tribe. This poison is also a neurotoxin with a mechanism of inhibition of sodium ion transport.
Saxitoxin (STX) is a nonprotein toxic compound, is insoluble in water and also have an inhibitory effect of sodium ion transport. This toxin has an effect equivalent to TTX. According to Groves et al (1980), STS and TTX produced by the dinoflagellate, though can also be found on a wide variety of marine life.
Other toxins such as Neosaxitoxin (neoSTX), brevetoxin, Surugatoxin, Nereistoxin, and Gonyautoxin also a neurotoxin that can be found in the crab's body although in very small amounts. These toxins are also found in the bodies of other animals such as clams and marine worms.
Why do the crab becomes toxic?
If we look at the classification of toxins, it can be concluded that while the actual producer of these toxins is not a species of crab. Some species produce toxins even algae. So, how can the crabs become toxic?Toxic crabs can be divided into two groups, namely toxic permanent (permanent toxicity properties) and temporary. The crabs are generally a member of the tribe Xanthidae. Crabs are known to be toxic permanent is Lopozozymus Pictor, Demania spp., Zosimus aeneus, Platypodia granulosa and Atergatis floridus. Meanwhile, crabs that are toxic Temporary example is Atergatis integerrimus and Atergatis spp. (All species except Atergatis Atergatis floridus). This temporary category crab toxic level of toxicity depends on habitat.
Until now there are at least two things that are believed to be the cause of the crabs become toxic, namely :
(1) contamination and accumulation of toxins from food consumption,(2) the effect of habitat (especially the presence of bacteria, algae and toxin-producing organisms).
Some studies in two or three decades ago mentioned that the main food source of dinoflagellate species are poisonous crabs, shellfish (bivalves and gastropods), worms (Polychaeta) as well as some species of algae. The consumption pattern of this kind can cause crabs accumulate these toxins because there are toxins such as TTX, STX and Okadaic acid produced by the dinoflagellate known.
How toxins from food can accumulate and why it did not cause toxicity in these crabs. The mechanism of exocytosis and endocytosis allegedly became a way for toxic substances accumulate in the body of the crab. Submitted that the toxic compound most commonly found in the liver and gonads crab intestine. Description of research Negri and Llewllyn that some species of the tribe Xanthidae has a defense mechanism against toxins (STX, TTX and turunanna). This mechanism is to produce proteins haemolimph are pharmacologically the same as saxiphilin, are compounds that can bind to toxins.
Habitat also affect the level of toxicity crab, especially crabs that are toxic temporary. The existence of algae, bacteria and toxin-producing organisms in a habitat can play an important role as a cause of crabs (as well as other animals such as shellfish and fish) become toxic. Bacteria such as Pseudomonas sp., Alteromonas sp., Moraxella sp., And Acinetobacter sp. known also capable of producing STX and neoSTX autonomously. Another group of bacteria known to produce TTX Vibrionaceae. These bacteria can be associated with crab (eg symbiotic and living in the section below the crab carapace) and lead to increased toxicity of the crab.
Furthermore, harmful algal population explosion events (especially those that can produce toxins) in a crab habitat can also cause increased toxicity crab. Crabs Xanthidae tribes generally have behavioral 'lazy' to move so that the limited range area. If the habitat is undergoing toxin-producing algal bloom, nature 'lazy' This move will increase the chances of contamination and accumulation of toxic compounds in the body of the crab.
Thank you for reading this article. Written and posted by Bambang Sunarno. sunarnobambang86@gmail.com
author:
https://plus.google.com/105319704331231770941.
name: Bambang Sunarno.
http://primadonablog.blogspot.com/2016/02/about-crabs.html
Publiushed Date: 07 February 2016 at 12:52
Code : 7MHPNPADAEFW
