Crustacean Life Cycle

Crustaceans develop from eggs to adults by going through a series of larval stages or instars. These stages are interspersed by full molts whereby they shed their exoskeleton and emerge a slightly larger and more complicated version of their previous form. Early larvae are plankton-dwelling creatures called nauplii that gradually develop various appendages. With each molt, the nauplii gains body segments and/or appendages gradually becoming more like its parent as it develops. Nauplii larvae do not feed, but utilize their internal yolk reserves from the egg for energy. Nauplii are the most abundant form of multicelluar life form on the planet.

Crustacean Anatomy

Crustaceans have compound eyes which are usually on the end of stalks. They have 2 pairs of antennae and a cuticle which is strengthened by calcium carbonate. A crustaceans head and thorax is most often covered by a carapace (shell) which extends forward to form a projection called a rostrum (a beaklike extension). Some crustaceans have additional mouthparts called maxillipeds. Unlike the internal skeletons of vertebrates, a crustaceans carapace or exoskeleton does not grow as the animal develops. Crustaceans have to molt periodically. During the molting process, every part of the body covering is shed including the covering of the eyes and fine hairs. Molting can be an exhausting ordeal and for some, things can go wrong. Some can become stuck in their old skin and the only option of escaping is to lose a claw or other appendage which unfortunately does not grow back.
A crustaceans thoracic appendages are called thoracopods and these are two branched and developed to perform various functions. These functions include feeding, moving, sensing the environment and for respiration by basal gills. The first pair of legs may be enlarged to form chelipads and are equipped with strong claws used for picking things up and defence.

Crustaceans (including: Decapods (crabs), Eucaridans (krill) and Malacostracans (woodlice and relatives)

The word crustacean means 'with a crust'. This group of arthropods is an extremely diverse group who range greatly in size from minute copepods which are only just visible to the naked eye to large lobsters and crabs such as the Giant Spider crab who has a leg span of up to 4 metres (13 feet). A vast majority of crustaceans live in the sea while others can survive in fresh water environments and on land. The most successful crustaceans live in the sea. One of the reasons they are more successful is that the sea contains essential minerals, such as calcium carbonate, which are needed for shell building. One crustacean that has adapted to life on land is the Woodlice. However, they do still live in damp places and can be found in rotting damp wood, under stones and in damp areas of houses.

Chelicerates (Arachnids - including spiders, scorpions, pseudoscorpions harvestmen, ticks and mites)

Arachnids have a head which is fused to their thorax forming a cephalothorax. The cephalothorax has sensory organs, mouthparts, limbs and stomach. The remaining body segments are fused to form an abdomen. The abdomen contains the heart, lungs, gut, reproductive organs and anus. This means that the body of an arachnid is only divided into 2 sections whereas insects have 3 body sections.
Arachnids use their sensory hairs, sensory organs and simple eyes to detect and analyse their surroundings. Arachnids are cold-blooded animals that get warmth from their environment.
Arachnids are diverse in size ranging from a few millimetres to 20 centimetres in length. They have a strong exoskeleton made of calcium and carbohydrates which protects them from predators. Arachnids do not possess teeth and most cannot digest solid foods, this is why they suck fluids from their preys body.
A scorpion has a tail that extends from their abdomen bearing a painful stinger on the end. At the front are 2 pincer-like chelicerae which are used to consume prey and a pair of limb-like pedipalps. They have 4 pairs of walking legs. Psuedoscorpions are not really scorpions although they have a similar appearance.
Pseudoscorpions do not have the extended tail with the stinging end, instead they produce venom from their pincer-like pedipalps. Pseudoscorpions also produce silk from silk glands which are located on the jaws or chelicerae. The silk is used to construct cocoons in which they molt and live during the winter. They usually range from 2 to 8 millimetres in length. The largest known species is Garypus titanius of Ascension Island at up to 12 millimetres.
Ticks are parasites that feed upon the blood of mammals such as humans, dogs, cows and sheep. Ticks are tiny arachnids, about the size of a grain of rice. They climb onto their host, gripping tightly with their legs and feed by sinking their mouthparts into the hosts skin and gorges itself on blood. Once the ticks body is full, it swells like a tiny balloon and falls off its host.
Most spiders are predatory arachnids that inject venom to catch their prey. Some spiders spin webs in order to catch their prey, others like the Brazilian Wandering spider walks the jungle floors in search of prey instead of residing in a lair or maintaining a web.

Millipedes

Millipedes are mostly herbivores or scavengers and have an elongated cylindrical or flattened body. The first 3 segments of a millipedes trunk contain no legs at all. The remaining segments are fused into pairs known as diplosegments and each diplosegment has 2 pairs of legs attached to it. Despite the millipedes common name, they never have a thousand legs.

Myriapods (including centipedes and millipedes)

Centipedes and millipedes have similar structured bodies whereby their form consists of a head and a body trunk made of similar shaped segments. These terrestrial creatures have biting mandibles, a single pair of antennae and they live in moist habitats as they do not have a waterproof cuticle. Centipedes are fast moving carnivores with an elongated, slightly flattened segmented body.
Each trunk segment consists of a pair of single legs. The first pair of legs on a centipedes trunk are modified as poisonous claws which they use to subdue their prey.