Jellyfish

Jellyfishes (also called jellies or sea jellies as they are not true fish) are animals that belong to Phylum Cnidaria, included in the class Scyphozoa. The name "jellyfish" is also sometimes used for the related classes of medusae (Hydrozoa) and box jellyfish (Cubozoa). Almost all jellyfish live in the seas and though they lack true organ structures they feature specialized tissues. The adult forms of these creatures are composed of 95-99% water. All species are found in each of the world's oceans, with a few species living in fresh water. Most jellyfish are passive drifters that feed on small fish and zooplankton that become caught in their tentacles. Jellyfish have an incomplete digestive system, meaning that the same orifice is used for both food intake and waste expulsion. They are Coelenterates which means "hollow gut", and are made up of a layer of epidermis, gastrodermis, and a thin jelly-like layer called mesoglea that separates the epidermis from the gastrodermis.

JellyfishThe jellyfish have two major body forms throughout their life. The first form is called the polyp stage and is characterized by a either a non-moving (sessile) stalk that catches food drifting by or a similar form that is free-floating. Their mouth and tentacles are located anteriorly, facing upwards. The second form looks like a saucer is called the medusa stage and is characterized by a round (radially symmetric) dome-shape body plan with food catching tentacles hanging down. It is this form which is most able to respond to and interact with its environment and is also the form most people are familiar with.

During the polyp stage, jellyfish do not have males or females, thus only asexual reproduction occurs. This happens in two ways: (1) budding, to produce other polyps; and (2) strobilating, to produce medusae. During budding, the egg or planula of the jellyfish attaches itself to a hard surface where it grows into its polyp form called scyphistoma. The scyphistoma then asexually produce many ephyra that look like round jagged disks and becomes a strobila. Then the ephyras detach themselves from the strobila and become mature free living medusae. At this stage is when they can reproduce sexually. The male will release their sperms into the water where the eggs will be fertilized.

Like all other cnidarians, jellyfish have stinging cells called cnidocytes which contains the stinging nematocysts on their tentacles. Whenever a prey comes in contact with a tentacle, hundreds to thousands of nematocysts fire one or another type of "hook and line" into the prey's direction. These stinging cells are thus able to latch onto the prey and the tentacles bring the prey item into their large "mouth" for digestion.These cells are activated by a simple but precise nervous system called a nerve net which is located in the epidermis of the jellyfish. Impulses to these nerve cells are sent from the nerve rings that have collected information from the environment of the jellyfish through the rhopalial lappet, which is located around the animal's body.

Jellyfish also have "eyes" or ocelli that cannot form images, but are sensitive to light. Jellyfish do not have a specialized digestive system, excretory system, respiratory system, and circulatory system. They are able to digest with the help of the gastrodermis that lines the gastrovascular cavity, where nutrients from their food is absorbed. They do not need a respiratory system since their skin is thin enough that oxygen can easily diffuse in and out of their bodies. They do not have a brain, a heart, a central nervous system, a skeletal system and also no bones and no blood. Jellyfish move using a hydrostatic skeleton that controls the water pouch in their body to manipulate their movements.

Most jellyfish are not dangerous to humans but a few are highly toxic, such as the Cyanea capillata. Contrary to popular belief, the menacingly infamous Portuguese Man O' War (Physalia) isn't actually a jellyfish, but a colony of hydrozoan polyps.

Crab

Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (Greek: brachy = short, ura = tail), or where the reduced abdomen is entirely hidden under the thorax. They are generally covered with a thick exoskeleton, and are armed with a single pair of chelae (claws). Crabs are found in all of the world's oceans; there are also many freshwater and terrestrial crabs, particularly in tropical regions. Crabs vary in size from the pea crab, only a few millimetres wide, to the Japanese spider crab, with a leg span of up to 4 m

True crabs have five pairs of legs, the first of which are modified into a pair of claws and are not used for locomotion. In all but a few crabs (for example, Raninoida), the abdomen is folded under the cephalothorax in the adult stage. The mouthparts of crabs are covered by flattened maxillipeds, and the front of the carapace does not form a long rostrum . The gills of crabs are formed of flattened plates ("phyllobranchiate"), resembling those of shrimp, but of a different structure .They can also be the size of a pea, or even smaller.

Most crabs show clear sexual dimorphism and so can be easily sexed. The abdomen, which is held recurved under the thorax, is narrow in males. In females, however, the abdomen retains a greater number of pleopods and is considerably wider . This relates to the carrying of the fertilised eggs by the female crabs (as seen in all pleocyemates). In those species in which no such dimorphism is found, the position of the gonopores must be used instead. In females, these are on the third pereiopod, or nearby on the sternum in higher crabs; in males, the gonopores are at the base of the fifth pereiopods or, in higher crabs, on the sternum nearby.

Crabs are omnivores, feeding primarily on algae , and taking any other food, including molluscs, worms, other crustaceans, fungi, bacteria and detritus, depending on their availability and the crab species. For many crabs, a mixed diet of plant and animal matter results in the fastest growth and greatest fitness.

Crabs make up 20% of all marine crustaceans caught and farmed worldwide, with over 1½ million tonnes being consumed annually. Of that total, one species accounts for one fifth: Portunus trituberculatus. Other important taxa include Portunus pelagicus, several species in the genus Chionoecetes, the blue crab (Callinectes sapidus), Charybdis spp., Cancer pagurus, the Dungeness crab (Cancer magister) and Scylla serrata, each of which provides more than 20,000 tonnes annually.

The infraorder Brachyura contains about 70 families, as many as the remainder of the Decapoda . The evolution of crabs is characterised by an increasing robustness of the body, and a reduction in the abdomen. Although other groups have also undergone similar processes of carcinisation, it is most advanced in crabs. The telson is no longer functional in crabs, and the uropods are absent, having probably evolved into small devices for holding the reduced abdomen tight against the sternum.

In most decapods, the gonopores (sexual openings) are found on the legs. However, since crabs use the first two pairs of pleopods (abdominal appendages) for sperm transfer, this arrangement has changed. As the male abdomen evolved into a narrower shape, the gonopores have moved towards the midline, away from the legs, and onto the sternum. A similar change occurred, independently, with the female gonopores. The movement of the female gonopore to the sternum defines the clade Eubrachyura, and the later change in the position of the male gonopore defines the Thoracotremata. It is still a subject of debate whether those crabs where the female, but not male, gonopores are situated on the sternum form a monophyletic group.

The earliest unambiguous crab fossils date from the Jurassic, although the Carboniferous Imocaris, known only from its carapace is thought to be a primitive crab. The radiation of crabs in the Cretaceous and afterwards may be linked either to the break-up of Gondwana or to the concurrent radiation of bony fish, the main predators of crabs.

About 850 species of crab are freshwater or (semi-)terrestrial species; they are found throughout the world's tropical and semi-tropical regions. They were previously thought to be a closely related group, but are now believed to represent at least two distinct lineages, one in the Old World and one in the New World

Several other groups of animals are either called crabs or have the term "crab" in their names. These include hermit crabs, porcelain crabs and king crabs, which, despite superficial similarities to true crabs, belong to the Anomura. The UK Food Standards Agency allows king crabs to be sold as "crab" , but this practice is not followed outside the food industry. Others, such as horseshoe crabs are much more distantly related. Anomuran "crabs" can be distinguished from true crabs by counting the legs. In Anomura, the last pair of pereiopods (walking legs) is hidden inside the carapace, so only four pairs are visible (counting the claws), whereas uninjured true crabs generally have five visible pairs (in the family Hexapodidae, the last pair of pereiopods is vestigial.

Starfish

Starfish or sea stars are any echinoderms belonging to the class Asteroidea. The names sea star and starfish are also (incorrectly) used for the closely related brittle stars, which make up the class Ophiuroidea.

Starfish exhibit a superficially radial symmetry. They typically have five or more "arms" which radiate from an indistinct disk (pentaradial symmetry). However, the evolutionary ancestors of echinoderms are believed to have had bilateral symmetry. Starfish do exhibit some superficial remnant of this body structure, evident in their larval pluteus forms.

Starfish do not rely on a jointed, movable skeleton for support and locomotion (although they are protected by their skeleton), but instead possess a hydraulic water vascular system that aids in locomotion. The water vascular system has many projections called tube feet on the ventral face of the starfish's arms which function in locomotion and aid with feeding.

The star fish usually hunt for shelled animals such as oysters and clams. They have two stomachs. One stomach is used for digestion, and the other stomach can be extended outward to engulf and digest prey. This feature allows the starfish to hunt prey that is much larger than its mouth would otherwise allow. Starfish are able to regenerate lost arms. A new starfish may be regenerated from a single arm attached to a portion of the central disk.

Starfish are composed of a central disc from which arms sprout in pentaradial symmetry. Most starfish have five arms, but some have more or fewer. Some starfish have shown differing numbers of limbs within a single species. The mouth is located underneath the starfish on the oral or ventral surface, while the anus is located on the top of the animal. The spiny upper surface is called the aboral or dorsal surface. On the aboral surface there is a structure called the madreporite, a small white spot located slightly off-center on the central disc which acts as a water filter and supplies the starfish's water vascular system with water to move. Porcellanasteridae employ additional cribriform organs used to generate current in the burrows made by these infaunal starfish.

While having their own basic body plan, starfish radiate diversely in shapes and colors, the morphology differing between each species. A starfish may have dense rows of spines as a means of protection, or it may have no spines at all. Ranging from nearly pentagonal (example: Indo-pacific cushion star, Culcita novaeguineae) to gracile stars like those of the Zoroaster genus.

Starfish have a simple photoreceptor eyespot at the end of each arm. The eye is only able to register differences of light and dark, which are useful in detecting movement.

Surrounding the spines on the surface of the starfish are small white objects known as pedicellariae. There are large numbers of these pedicellariae on the external body which serve to prevent encrusting organisms from colonizing the starfish. The radial canal which is across each arm of the starfish has tooth-like structures called ampullae, which surround the radial canal. Patterns including mosaic-like tiles formed by ossicles, stripes, interconnecting net between spines, pustules with bright colors, mottles or spots. These mainly serve as camouflage or warning coloration which is displayed by many marine animals as a means of protection against predation. Several types of toxins and secondary metabolites have been extracted from several species of starfish. Research into the efficacy of these compounds for possible pharmacological or industrial use occurs worldwide.

The body cavity also contains the water vascular system that operates the tube feet, and the circulatory system, also called the hemal system. Hemal channels form rings around the mouth (the oral hemal ring), closer to the top of the starfish and around the digestive system (the gastric hemal ring). A portion of the body cavity called the axial sinus connects the three rings. Each ray also has hemal channels running next to the gonads.

Starfish digestion is carried out in two stomachs: the cardiac stomach and the pyloric stomach. The cardiac stomach is a sack like stomach located at the center of the body and may be everted out of the organism's body to engulf and digest food. Some species are able to use their water vascular systems to force open the shells of bivalve mollusks such as clams and mussels by injecting their stomachs into the shells. With the stomach inserted inside the shell, the starfish is able to digest the mollusk in place. The cardiac stomach is then brought back inside the body, and the partially digested food is moved to the pyloric stomach. Further digestion occurs in the intestine. Waste is either excreted through the anus on the aboral side of the body, or excreted through the mouth if the anus is absent as in brittle stars.

Because of this ability to digest food outside of its body, the sea star is able to hunt prey that are much larger than its mouth would otherwise allow, including arthropods, small fish, and mollusks.

Some echinoderms live several weeks without food under artificial conditions. It is believed that they may receive some nutrients from organic material dissolved in seawater.

Sea stars and other echinoderms have endoskeletons, suggesting that echinoderms are very closely related to chordates; animals with a hollow nerve chord that usually have vertebrae.

Echinoderms have rather complex nervous systems, but lack a true centralized brain. All echinoderms have a network of interlacing nerves called a nerve plexus which lies within as well as below the skin. The esophagus is also surrounded by a number of nerve rings which send radial nerves that are often parallel with the branches of the water vascular system. The ring nerves and radial nerves coordinate the starfish's balance and directional systems. Although the echinoderms do not have many well-defined sensory inputs, they are sensitive to touch, light, temperature, orientation, and the status of water around them. The tube feet, spines, and pedicellariae found on starfish are sensitive to touch, while eyespots on the ends of the rays are light-sensitive.

Most species are generalist predators, some eating clams, and oysters; or any animal too slow to evade the attack (e.g. dying fish). Some species are detritivores, eating decomposed animal and plant material or organic films attached to substrate. The others may consume coral polyps (the best-known example for this is the infamous Acanthaster planci), sponges or even suspended particles and planktons (starfish from the Order Brisingida). The processes of feeding and capture may be aided by special parts; Pisaster brevispinus or Short-spined Pisaster from the west coast of America may use a set of specialized tube feet to extend itself deep into the soft substrata to extract prey (usually clams). Grasping the shellfish, the Starfish slowly pries open the shell by wearing out the Adductor muscle and then inserts an arm into an opening to devour the organism.

Starfish are capable of both sexual and asexual reproduction. Individual starfish are male or female. Fertilization takes place externally, both male and female releasing their gametes into the environment. Resulting fertilized embryos form part of the zooplankton.

Starfish are developmentally (embryologically) known as deuterostomes. Their embryo initially develops bilateral symmetry, indicating that starfish probably share a common ancestor with the chordates, which includes the fish. Later development takes a very different path however as the developing starfish settles out of the zooplankton and develops the characteristic radial symmetry. Some species reproduce cooperatively, using environmental signals to coordinate the timing of gamete release; in other species, one to one pairing is the norm.

Some species of starfish also reproduce asexually by fragmentation, often with part of an arm becoming detached and eventually developing into an independent individual starfish. This has led to some notoriety. Starfish can be pests to fishermen who make their living on the capture of clams and other mollusks at sea as starfish prey on these. The fishermen would presumably kill the starfish by chopping them up and disposing of them at sea, ultimately leading to their increased numbers until the issue was better understood. A starfish arm can only regenerate into a whole new organism if some of the central ring of the starfish is part of the chopped off arm.

Starfish move using a water vascular system. Water comes into the system via the madreporite. It is then circulated from the stone canal to the ring canal and into the radial canals. The radial canals carry water to the ampullae and provide suction to the tube feet. The tube feet latch on to surfaces and move in a wave, with one body section attaching to the surfaces as another releases. Most starfish cannot move quickly. However, some burrowing species like starfish from genus Astropecten and Luidia are capable of rapid, creeping motion: "gliding" across the ocean floor. This motion results from their pointed tubefeet adapted specially for excavating patches of sand.

Some species of starfish have the ability to regenerate lost arms and can regrow an entire new arm in time. Most species must have the central part of the body intact to be able to regenerate, but a few can grow an entire starfish from a single ray. Included in this group are the red and blue Linckia star. The regeneration of these stars is possible due to the vital organs kept in their arms.

Fossil starfish and brittle stars are first known from rocks of Ordovician age indicating that two groups probably diverged in the Cambrian. However, Ordovician examples of the two groups show many similarities and can be difficult to distinguish. Complete fossil starfish are very rare, but where they do occur they may be abundant. Most fossil starfish consist of scattered individual plates or segments of arms. This is because the skeleton is not rigid, as in the case of echinoids (sea urchins), but is composed of many small plates (or ossicles) which quickly fall apart and are scattered after death and the decay of the soft parts of the creature. Scattered starfish ossicles are reasonably common in the Cretaceous Chalk Formation of England.

There are about 1,800 known living species of starfish, and they occur in all of the Earth's oceans. The greatest variety of starfish is found in the tropical Indo-Pacific. Areas known for their great diversity include the tropical-temperate regions around Australia, the tropical East Pacific, and the cold-temperate water of the North Pacific (California to Alaska). Asterias is a common genus found in European waters and on the eastern coast of the United States; Pisaster, along with Dermasterias ("leather star"), are usually found on the western coast. Habitats could range from tropical coral reefs, kelp forests to deep-sea floor, although none of them live within the water column; all species of starfish found are living as benthos. Echinoderms need a delicate internal balance in their body; no starfish are found in freshwater environments.

Anemone Tentacles

Sea anemones are a group of water dwelling, predatory animals of the order Actiniaria; they are named after the anemone, a terrestrial flower. As cnidarians, sea anemones are closely related to corals, jellyfish, tube-dwelling anemones and Hydra.

A sea anemone is a small sac, attached to the bottom by an adhesive foot, with a column shaped body ending in an oral disc. The mouth is in the middle of the oral disc, surrounded by tentacles armed with many cnidocytes, which are cells that function as a defense and as a means to capture prey. Cnidocytes contain cnidae, capsule-like organelles capable of everting, giving phylum Cnidaria its name. The cnidae that sting are called nematocysts. Each nematocyst contains a small vesicle filled with toxins—actinoporins—an inner filament and an external sensory hair. When the hair is touched, it mechanically triggers the cell explosion, a harpoon-like structure which attaches to organisms that trigger it, and injects a dose of poison in the flesh of the aggressor or prey. This gives the anemone its characteristic sticky feeling.

The poison is a mix of toxins, including neurotoxins, which paralyze the prey, which is then moved by the tentacles to the mouth/anus for digestion inside the gastrovascular cavity. Actinoporins have been reported as highly toxic to fish and crustaceans, which may be the natural prey of sea anemones. In addition to their role in predation, it has been suggested that actinoporins could act, when released in water, as repellents against potential predators. Clownfish are immune to an anemone's sting.

The internal anatomy of anemones is simple. There is a gastrovascular cavity (which functions as a stomach) with a single opening to the outside which functions as both a mouth and an anus: waste and undigested matter is excreted through the mouth/anus. A primitive nervous system, without centralization, coordinates the processes involved in maintaining homeostasis as well as biochemical and physical responses to various stimuli. Anemones range in size from less than 1¼ cm (½ in) to nearly 2 m (6 ft) in diameter.[citation needed] They can have a range of 10 tentacles to hundreds.

The muscles and nerves in anemones are much simpler than those of other animals. Cells in the outer layer (epidermis) and the inner layer (gastrodermis) have microfilaments grouped together into contractile fibers. These are not true muscles because they are not freely suspended in the body cavity as they are in more developed animals. Since the anemone lacks a skeleton, the contractile cells pull against the gastrovascular cavity, which acts as a hydrostatic skeleton. The stability for this hydrostatic skeleton is caused by the anemone shutting its mouth, which keeps the gastrovascular cavity at a constant volume, making it more rigid.

Unlike other cnidarians, anemones (and other anthozoans) entirely lack the free-swimming medusa stage of the life cycle: the polyp produces eggs and sperm, and the fertilized egg develops into a planula that develops directly into another polyp.

A few anemones are parasitic to marine organisms. Anemones tend to stay in the same spot until conditions become unsuitable (prolonged dryness, for example), or a predator is attacking them. In the case of an attack, anemones can release themselves from the substrate and swim away to a new location using flexing motions.

The sexes in sea anemones are separate for some species while some are hermaphroditic. Both sexual and asexual reproduction may occur. In sexual reproduction males release sperm which stimulates females to release eggs, and fertilization occurs. The eggs or sperm are ejected through the mouth. The fertilized egg develops into a planula, which finally settles down and grows into a single anemone. They can also reproduce asexually by budding, binary fission, which involves pulling apart into two halves, and pedal laceration, in which small pieces of the pedal disc break off and regenerate into small anemones.

The sea anemone has a foot which in most species attaches itself to rocks or anchors in the sand. Others also burrow into a stronger object. Some species attach to kelp and others are free-swimming. Although not plants and therefore incapable of photosynthesis themselves, many sea anemones form an important facultative symbiotic relationship with certain single-celled green algae species which reside in the animals' gastrodermal cells. These algae may be either zooxanthellae, zoochlorellae or both. The sea anemone benefits from the products of the algae's photosynthesis, namely oxygen and food in the form of glycerol, glucose and alanine; the algae in turn are assured a reliable exposure to sunlight and protection from micro-feeders, which the anemones actively maintain. The algae also benefit by being protected due to the presence of stinging cells called nematacysts, reducing the likelihood of being eaten by herbivores. Most species inhabit tropical reefs, although there are species adapted to relatively cold waters, intertidal reefs, and sand/kelp environments.

Lionfish

A Lionfish is any of several species of venomous marine fish in the genera Pterois, Parapterois, Brachypterois, Ebosia or Dendrochirus, of the family Scorpaenidae. The lionfish is also known as the Turkey Fish, Dragon Fish, and Scorpion Fish. The lionfish are voracious predators. When they are hunting, they corner prey using their large fins and then use their lightning quick reflexes to swallow the prey whole. They are notable for their extremely long and separated spines, and have a generally striped appearance, red, brown, orange, yellow, black, or white.

The group of fish has been classified as a subfamily (Pteroinae) or as a tribe under Scorpaeninae (Pteroini).

While the hardiness and disease resistance of the lionfish make their care relatively simple, the venom of the spines is extremely painful, and lionfish are recommended for only the careful aquarist.

The lionfish is native to the tropical Indo-Pacific region of the world, but various species can be found worldwide. Due to a recent introduction, the lionfish has recently been spotted in the warmer coral regions of the Eastern Atlantic Ocean and Caribbean Sea. Successful breeding of the lionfish in captivity has not been reported.