 |
| Diversity of Arthropods(R) |
Arthropods' primary internal cavity is a hemocoel, which accommodates their internal organs and through which their blood circulates; they have open circulatory systems. Like their exteriors, the internal organs of arthropods are generally built of repeated segments. Their nervous system is "ladder-like", with paired ventral nerve cords running through all segments and forming paired ganglia in each segment. Their heads are formed by fusion of varying numbers of segments, and their brains are formed by fusion of the ganglia of these segments and encircle the esophagus. The respiratory and excretory systems of arthropods vary, depending as much on their environment as on the subphylum to which they belong.
Their vision relies on various combinations of compound eyes and pigment-pit ocelli: in most species the ocelli can only detect the direction from which light is coming, and the compound eyes are the main source of information, but the main eyes of spiders are ocelli that can form images and, in a few cases, can swivel to track prey. Arthropods also have a wide range of chemical and mechanical sensors, mostly based on modifications of the many setae (bristles) that project through their cuticles.
Marine Spider
 |
| Marine Spider |
This little spider is commonly seen on many of our shores: on rocky shores, coral rubble areas and reefs. It is more active at night. The most common of these 'marine spiders' belong to the genus Desis, they survive by building silk chambers in air-filled pockets in rock cavities, shells and seaweed holdfasts. At low tide they emerge to feed on small crustaceans or anything else they can handle with their large jaws.
Features: Body to about 1cm. The spider has long furry legs. It is greyish sometimes with a pink tinge. At high tide, it hides in air pockets among crevices of submerged rocks. It emerges at low tide to hunt. It can 'walk' on water, scuttling rapidly over the water. Its hairy feet prevent it from breaking the water surface tension.
Hermit Crab
 |
| Hermit Crab |
 |
| Hermit Crab in a cone snail's shell |
The hermit crab is a type of crab that doesn't have a hard exoskeleton. Not a true crab, it uses other animals' old shells for protection; they especially like old whelk shells. As the hermit crab grows in size, it must find a larger shell, hence its name "hermit".
The hermit crab is a crustacean; there are about 500 different species of hermit crabs around the world. Most hermit crab species live on the ocean floor, but many live on land. Female terrestrial (land based) hermit crabs must return to the sea to breed.
Anatomy: Hermit crabs are invertebrates, animals without a backbone. They have an exoskeleton, an outer shell that provides support for their body but does not provide much protection from predators. They vary widely in color, from red to brown to purple, with stripes, dots, and other patterns. They have ten jointed legs; the front two legs have large, grasping claws (called pincers or chelipeds) and the rear pair of legs are very small. They have a flattened body, sensory antennae, two eyes located at the ends of stalks, and a soft, twisted abdomen (which the hermit crab keeps hidden inside its shell).
Diet: Hermit crabs are omnivores (eating plants and animals) and scavengers (eating dead animals that they find). They eat worms, plankton, and organic debris.
Elbow crabs
Phylum: Arthropoda
Phylum: Arthropoda
Subphylum: Crustacea
Class: Malacostraca
Order: Decapoda
Family: Parthenopidae
Elbow crabs are small (being only 1 - 2 cm in width) and slow-moving creatures. They are well camouflaged, and look like dirt or junk among seaweeds, where they usually are found at. They are somewhat triangular or pentagonal in body shape, and have thin walking legs which are pointed and small. Tubeworms or small algae bits may even grow from its body.
Its highly elongated pincers (and large, relative to the crab's size) stick out from the sides of its body, earning its name. Its upper "finger" is movable and curved towards the immovable lower "finger". Males usually have larger pincers than females. The pincers are capable of doing serious damage to small prey, such as worms, small snails and clams (their diet). The inner surface of each pincer has a row of coloured spots and bumps might be used to camouflauge its weapon from damage from predators, as it is well camouflauged among mud and sand.
They play a rather important role in habitat, being a secondary consumer. They feed on small creatures that feed on plants, and larger creatures highly depend on them for food. Being so small, they can live in soft corals and even sea urchins.
Some of elbow crabs species have been listed in the threatened animals of Singapore, despite being a common sight in Singapore's northern shores. Just like many other creatures in the inter tidal zone, they are threatened by human activities such as land reclamation and pollution. Unobservant visitors also trample many to death, as Singapore shores are widely visited by students and tourists.
 |
| Elbow Crab salute |
Snapping Shrimp
Snapping Shrimp cleaning its cave
Fully grown snapping shrimp
Snapping Shrimps possess large asymmetrical claws used to snap at passing prey. Their claws are able to temporarily shock small passing fishes, by releasing a compressed pocket of air trapped within their claws. This produces the characteristic pop sound often heard in intertidal areas. The Snapping Shrimp can be found along the intertidal areas. They dig into the sand to make a burrow to live in. They are known to be good housekeepers and like to remove dirt and debri from their burrows. They are most common for their symbiotic relationships with Goby. For more information on this symbiotic relationship, please view the post on Goby.
Blue Swimmer Crabs
On our trip to Pulau Hantu, we saw the remains of an exoskeleton of a Blue Swimmer Crab that just moulted out of its exoskeleton. Our guide, Robert, told us the methods to use to identify whether it was actually a dead body or a skin that the crab moulted. He would smell the exoskeleton and see whether the crab shell would smell like rotting or dead flesh. If not, it would most probably be a shell that a crab just shed out. Another thing that Robert told us was how to identify whether a crab was a male or a female. We would look at the underside of the crab to identify its gender. If the underside of the crab looks like this:
 |
| Underside of male Blue Swimmer Crab |
 |
| Live Crab |
Dead crab
Fiddler Crabs
Fiddler crab hole
Fiddler Crabs retreat into their holes, coralsnake in the distance
The Fiddler Crab is in the same order as the Snapping Shrimp: Decapoda. They have asymmetrical pincers, one extensively large and the other very small in comparison This trait only applies to the male as the large pincers are used in the process of mating and courtship. The bigger the claw, the easier it is to find a mate. The fiddler crabs also use their pincers occasionally for fighting. Another use for their claws is for occasionally catching small fish as food. They live along the intertidal areas of the coastline and dig burrows under the sand.
The Fiddler Crab is in the same order as the Snapping Shrimp: Decapoda. They have asymmetrical pincers, one extensively large and the other very small in comparison This trait only applies to the male as the large pincers are used in the process of mating and courtship. The bigger the claw, the easier it is to find a mate. The fiddler crabs also use their pincers occasionally for fighting. Another use for their claws is for occasionally catching small fish as food. They live along the intertidal areas of the coastline and dig burrows under the sand.
Ghost Crab
As their name suggests, these critters are elusive creatures normally found on the coastline of many tropical areas. They tend to burrow into the sand with a hole that is approximately 1 meter in depth. This is their burrow. Furthermore, they also dig an extra entrance to the tunnel that is covered by debri that is located somewhere further up/down from the original hole. This is to provide the Ghost Crab with an extra escape route if its original hole is blocked or inaccessible. They are nocturnal animals that come out at night to hunt for food along the coast and shoreline.
Ghost crab hole
Horseshoe Crabs
 |
| Underside of Horseshoe Crab |
The horseshoe crab's central mouth is surrounded by its legs and while harmless, it is advisable to handle a horseshoe crab with care since you could pinch your fingers between the two parts of its shell while holding it.Once called "Horsefoot Crabs" because of the resemblance of its shell to a horse hoof, the Horseshoe Crab isn't really a crab. Related to scorpions, ticks and land spiders, horseshoe crabs have their own classification (Class Merostomata).
They look dangerous don't they? With their spines,menacing tail and armoured body they move around and smash through little organisms and gobble them up. Right? If you think that was true that look again. Despite their size and intimidating appearance, horseshoe crabs are not dangerous. A horseshoe crab's tail, while menacing, is not a weapon. Instead, the tail is used to plow the crab through the sand and muck, to act as a rudder, and to right the crab when it accidentally tips over.
Horseshoe crabs can also swim upside down in the open ocean using their dozen legs (most with claws) and a flap hiding nearly 200 flattened gills to propel themselves.
http://www.beach-net.com/horseshoe/Bayhorsecrab.html/
http://australianmuseum.net.au/Arachnology-Collection-Mysterious-Marine-Spiders-in-Sydney-Harbour
http://en.wikipedia.org/wiki/Arthropod
http://en.wikipedia.org/wiki/Arthropod
No comments:
Post a Comment