Arthropods 2BIbDF09 10/11

What is an Arthropod?

Arthropods are eukaryotic multicellular heterotrophic organisms that obtain nutrients by ingestion. Arthropods are members of the most diverse phylum in the animal kingdom. They are named for their jointed appendages, which enable these animals to move despite their hard outer covering, the exoskeleton and have a segment body.

PICTURE needed. Head-Thorax-Abdoden

What is Arthropod's jointed appendages?

Limbs are a prominent feature of species in many phyla. They are particularly important in two major lineages: the ecdysozoans and the vertebrates. Some members of the Ecdysozoa, such as arthropods, have more complex, jointed limbs, which make fast, precise walking, running, jumping movements possible and are a prominent limb type in vertebrates and arthropods. Arthropod's appendages of different segments are variously adapted for walking, feeding, sensory reception, reproduction, swimming and defense. Thanks to the evolutionary flexibility of their segments and appendages, it contributes to the great diversification of arthropods.

PICTURE of appendages needed

What is the diversification of Arthropods?

The estimation about the total arthropod population numbers is a billion billion individuals, but only a million species has identified, mostly insects. They must be regarded as the most successful animal phylum. The major groups of Arthropods are Arachnids, Crustaceans, Millipedes and Centipedes, and Insects.

what are the differences between these five groups?

Arachnids usually have four pairs of walking legs and specialized pair of feeding appendages. Crustaceans are almost all marine organisns but some live in fresh water or in a terrestrial environment. They all have a crustacean hallmark of multiple pairs of specialized appendages. Millipeds eat decaying plantmatter. Centripeds are carnivores are the only arhtropods without atenna . They have a pair of poison claws and a dsingle pair of long legs. Both (millipeds and centripeds)have segmented body and jointed legs. Insects have six legs and mostly have two pairs of wings.

{{co|Maybe you could mention the main characteristics of each group.}

What are the main characteristics of animals?

Where do they live?

Arthropods live

How do they feed?

Arthropds feed with dead or alive organisms. (to develop...)

How do they reproduce?

Arachnids

The male weaves a web on which it is going to deposit its sperm. It leaves then in search of a partner. After the coupling, the female eats generally its partner (source of food).

Crustaceans

Females spawn. Larvas ( called nauplius ) moult several times before reaching the adult stage. This process occurs most of the times, but some crustaceans are however hermaphrodits.

Millipedes, Centipedes, and Insects

Millipedes, centipedes and insects spawn, with extern fertilization. As crustaceans, insects pass by several embryonic stages before reaching the adult stage. In certain species, larvas look like the adults (ametaboles insects). Others undergo a metamorphosis. The metamorphosis is incomplete by hemimétaboles (3 stages: egg, larva, adult. The larva looks like the adult but has no wings) and complete by holometaboles (4 stages: egg, larva, nymph, adult. The larva is completely different from the adult).