Phylum Arthropoda chitin exoskeleton jointed appendages repeated segments open circulatory system more than 10 million species respiratory system varies with subphlyum
Arthropods are everywhere Two out of every three known species of animals are arthropods Members of the phylum Arthropoda are found in nearly all habitats of the biosphere Science Mag - Life's Pagent Not so Rich www.brighthub.com news.sciencemag.org
Arthropod Origins The arthropod body plan consists of a segmented body, hard exoskeleton, and jointed appendages, and dates to the Cambrian explosion (535 525 million years ago) Early arthropods the Trilobites show little variation from segment to segment
Arthropods have an open circulatory system in which fluid called hemolymph is circulated into the spaces surrounding the tissues and organs A variety of organs specialized for gas exchange have evolved in arthropods
Molecular evidence suggests that living arthropods consist of four major lineages that diverged early in the phylum s evolution: Subphylum Cheliceriforms (sea spiders, horseshoe crabs, scorpions, ticks, mites, and spiders) Subphlym Mandibulata Class Myriapods (centipedes and millipedes) Class Hexapods (insects and relatives) Class Crustaceans (crabs, lobsters, shrimps, barnacles, and many others)
Arthropoda: Cheliceriforms Cheliceriforms,, are named for clawlike feeding appendages called chelicerae Most marine cheliceriforms (including eurypterids) are extinct, but some species survive today, including horseshoe crabs
Fig. 33-30 Cheliceriforms Horseshoe crabs (class Merostomata) www.enchantedlearning.com -
Arthropoda: Cheliceriforms Most modern cheliceriforms are arachnids, which include spiders, scorpions, ticks, and mites Scorpion 50 µm Dust mite spider
Class Arachnida Closer look at the Order Araneae abdomen and a cephalothorax, which has six pairs of appendages, the most anterior of which are the chelicerae (4 pairs legs) Gas exchange in spiders occurs in respiratory organs called book lungs www.education.com
Many spiders spin silk others are ambush predators or spin a funnel and wait for prey to fall into the trap http://upload.wikimedia.org/wikipedia/co mmons/f/f9/spiders_diversity.jpg
Class Arachnida Closer look at the Order Solifugae Contrary to popular myth, these scary looking Arachnids do not possess venom, nor do they eat American solders or camels. http://www.camelspiders.net/large-camel-spider-picture.htm Urban Legends - Camel Spider
Arthropoda: Myriapods Myriapods are terrestrial, and have jaw-like mandibles Millipedes, class Diplopoda, Each trunk segment has two pairs of legs Centipedes, class Chilopoda, are carnivores They have one pair of legs per trunk segment
Arthropoda: Class Hexapoda Insects The Hexapoda, (insects) has more species than all other forms of life combined They live in almost every terrestrial habitat and in fresh water bioinf.nuim.ie
Fig. 33-35 Abdomen Thorax Head Compound eye Antennae Anus Heart Cerebral ganglion Dorsal artery Crop Vagina Malpighian tubules Ovary Tracheal tubes Nerve cords Mouthparts
Flight is one key to the great success of insects An animal that can fly can escape predators, find food, and disperse to new habitats much faster than organisms that can only crawl
Insects undergo metamorphosis during their development In incomplete metamorphosis, the young, called nymphs, resemble adults Insects with complete metamorphosis have larval stages known by such names as maggot, grub, or caterpillar
Fig. 33-37
Arthropoda: Crustaceans While arachnids and insects thrive on land, crustaceans, for the most part, have remained in marine and freshwater environments Crustaceans typically have branched appendages that are extensively specialized for feeding and locomotion Most crustaceans have separate males and females
Isopods include terrestrial, freshwater, and marine species Pill bugs are a well known group of terrestrial isopods Some others are freakish parasites! http://www.treehugger.com/natural-sciences/bizarre-tongueeating-parasite-discovered-off-the-jersey-coast.html
Fig. 33-38 Decapods are all relatively large crustaceans and include lobsters, crabs, crayfish, and shrimp (a) Ghost crab (b) Krill (c) Barnacles