Phylum ARTHROPODA
Arthropoda is the largest phylum in the Animal Kingdom. Some well known arthropods include insects, crustaceans and spiders.
ECOLOGICAL ROLE
Arthropods are of immense importance to the ecology of the whole planet. Without them, complicated multicellular life on this planet would simply collapse and disappear. They are important in nutrient cycling in both aquatic and terrestrial environments. They supply food directly for amphibians, fish, birds, mammals and reptiles.
Arthropods are of immense importance to the ecology of the whole planet. Without them, complicated multicellular life on this planet would simply collapse and disappear. They are important in nutrient cycling in both aquatic and terrestrial environments. They supply food directly for amphibians, fish, birds, mammals and reptiles.
MOVEMENT STRUCTURES/TYPE
Most arthropods move by means of their segmented appendages, the exoskeleton and the muscles, which attach to the inside of the skeleton, together acting as a lever system. Specialized body segments called tagma allow for highly controlled movement. The exoskeleton provides a large surface area for the attachment of muscles and, in addition to functioning in support and movement, also provides protection from the external environment. Appendages of arthropods have been adapted for all types of locomotion—walking, pushing, running, swimming, and burrowing. Insect wings are not segmental appendages as are the legs. The paired wings arise as lateral folds of the integument, one pair above each of the last two pairs of legs. Each wing thus consists of an upper and lower sheet of exoskeleton closely applied to each other.
Most arthropods move by means of their segmented appendages, the exoskeleton and the muscles, which attach to the inside of the skeleton, together acting as a lever system. Specialized body segments called tagma allow for highly controlled movement. The exoskeleton provides a large surface area for the attachment of muscles and, in addition to functioning in support and movement, also provides protection from the external environment. Appendages of arthropods have been adapted for all types of locomotion—walking, pushing, running, swimming, and burrowing. Insect wings are not segmental appendages as are the legs. The paired wings arise as lateral folds of the integument, one pair above each of the last two pairs of legs. Each wing thus consists of an upper and lower sheet of exoskeleton closely applied to each other.
BODY COVERING; CELL LAYERS; LEVEL OF ORGANIZATION; PROTECTION
Arthropods are multicellular, triploblastic, bilaterally symmetrical protostomes with segmented bodies. Each body segment has a pair of segmented appendages that are joint. Some appendages have formed other structures such as mouthparts or antennae. Arthropods come from a lineage of animals that have a coelom; a membrane-lined cavity between the gut and the body wall that accommodates the internal organs. A number of segments are fused together to form integrated body parts such as the head, and abdomen through a process called tagmosis.
SUPPORT; MAINTAINING BODY SHAPE
Arthropod bodies are covered with an exoskeleton made up primarily of chitin that is covered in a waxy cuticle. It provides both support and protection for the organism. The exoskeleton cannot stretch which restricts growth. Therefore, arthropods continuously replace their exoskeletons by moulting or shedding the old exoskeleton after growing a new one that is not yet hardened, through a process called ecdysis. While moulting, arthropods must remain hidden to avoid predation.
Arthropod bodies are covered with an exoskeleton made up primarily of chitin that is covered in a waxy cuticle. It provides both support and protection for the organism. The exoskeleton cannot stretch which restricts growth. Therefore, arthropods continuously replace their exoskeletons by moulting or shedding the old exoskeleton after growing a new one that is not yet hardened, through a process called ecdysis. While moulting, arthropods must remain hidden to avoid predation.
OBTAINING NUTRIENTS
Arthropoda include carnivores, herbivores, detritus feeders, filter feeders and parasites. Most have a complete digestive system with a complete gut, a mouth, and an anus. Typically, paired appendages around the mouth are used for collecting and handling food, and are usually specialized in accordance with the particular diet of the animal. For example, the insect family Aphididae has mouthparts adapted for piercing vegetation and sucking out plant juices. Some crustaceas have "teeth" in their stomach. A number of carnivorous arthropods such as spiders and scorpions capture prey with poison, which is delivered with a pair of appendages; scorpions use their stinger and spiders use their fangs.
Arthropoda include carnivores, herbivores, detritus feeders, filter feeders and parasites. Most have a complete digestive system with a complete gut, a mouth, and an anus. Typically, paired appendages around the mouth are used for collecting and handling food, and are usually specialized in accordance with the particular diet of the animal. For example, the insect family Aphididae has mouthparts adapted for piercing vegetation and sucking out plant juices. Some crustaceas have "teeth" in their stomach. A number of carnivorous arthropods such as spiders and scorpions capture prey with poison, which is delivered with a pair of appendages; scorpions use their stinger and spiders use their fangs.
RESPIRATION
Respiration of aquatic arthropods takes place through the body surface and or by means of gills, tracheae or lungs. Terrestrial arthropods have a system of tubules, which are spiracles connected to trachea that provide gas exchange between tissues. Small species often do not have any and enable simple diffusion through the body surface to supply enough oxygen. Crustacea usually have gills, arachnids have book lungs and many insects have tracheae systems that run from the openings in the body walls, deliver oxygen directly to individual cells.
Respiration of aquatic arthropods takes place through the body surface and or by means of gills, tracheae or lungs. Terrestrial arthropods have a system of tubules, which are spiracles connected to trachea that provide gas exchange between tissues. Small species often do not have any and enable simple diffusion through the body surface to supply enough oxygen. Crustacea usually have gills, arachnids have book lungs and many insects have tracheae systems that run from the openings in the body walls, deliver oxygen directly to individual cells.
CIRCULATION
The circulatory system is open and consists of a heart, arteries and a system of arteries. Arthropods’ internal cavity is a hemocoel, which holds their internal organs, and through which their blood circulates. The arteries deliver blood into tissue spaces (hemocoels) which eventually gets returned back into the heart. In chelicerates and crustaceans, the blood carries oxygen to the tissues, while the insects use a separate system of tracheae.
The circulatory system is open and consists of a heart, arteries and a system of arteries. Arthropods’ internal cavity is a hemocoel, which holds their internal organs, and through which their blood circulates. The arteries deliver blood into tissue spaces (hemocoels) which eventually gets returned back into the heart. In chelicerates and crustaceans, the blood carries oxygen to the tissues, while the insects use a separate system of tracheae.
EXCRETION
Aquatic arthropods excrete waste via any permeable membrane but mainly through the gills. Waste is excreted through the green gland in crustaceans. Terrestrial arthropods malpighian tubules filter the waste, which is then dumped into the hindgut, from which they are expelled as feces.
Aquatic arthropods excrete waste via any permeable membrane but mainly through the gills. Waste is excreted through the green gland in crustaceans. Terrestrial arthropods malpighian tubules filter the waste, which is then dumped into the hindgut, from which they are expelled as feces.
RESPONSE
The nervous system is annelid like with a brain and a nerve ring surrounding the pharynx that connects the brain with a pair of ventral nerve cords. Paired ventral nerve cords running through all segments and forming paired ganglia in each segment. They have a variety of organs present including antennae, sensory brittles, and ears. Most arthropods have visual systems that include both of compound eyes and ocelli (little eyes). In most cases, ocelli are only capable of detecting the direction from which light is coming. However the ocelli of spiders are capable of forming images which can be used to rotate and track prey. Compound eyes consist of thousands of independent hexagonal ommatidia columns that each act as a sensor capable of detecting light, movement, and colour.
The nervous system is annelid like with a brain and a nerve ring surrounding the pharynx that connects the brain with a pair of ventral nerve cords. Paired ventral nerve cords running through all segments and forming paired ganglia in each segment. They have a variety of organs present including antennae, sensory brittles, and ears. Most arthropods have visual systems that include both of compound eyes and ocelli (little eyes). In most cases, ocelli are only capable of detecting the direction from which light is coming. However the ocelli of spiders are capable of forming images which can be used to rotate and track prey. Compound eyes consist of thousands of independent hexagonal ommatidia columns that each act as a sensor capable of detecting light, movement, and colour.
REPRODUCTION
Few arthropods such as barnacles are hermaphroditic, however individuals of most species remain one sex for their entire life. Most species reproduce sexually either through internal or external fertilization. All terrestrial arthropods use internal fertilization and lay eggs, except for scorpions; they produce live young after the eggs have hatched inside the mother. Some species use modified appendages such as gonopods or penises to transfer the sperm directly into the female. But most arthropods produce spermatophores, waterproof packets of sperm which the female then take into their bodies.
Classes of Arthropoda
Arachnida: Second largest group of land arthropods, species include scorpions, spiders, ticks and mites, they have paired jointed appendages and a hardend exoskeleton, body consists of a fused head and thorax and abdomen, claw like fangs near the mouth, mouth parts and then walking legs, breathe by means of book lungs and or tracheae (small tubes that distribute air from outside throughout the body), pierce the body of prey and consuming its body fluids or predigest the food by digestive secretions.
Insecta: Account for the vast majority of animal species on Earth, species include bees, ants, mosquitos, butterflys, segmented body composed of three tagmata, head, thorax and abdomen, compound eyes, antennae, three ocelli on the head, mouthparts, mandibles, one or two pairs of wings, three pairs of walking legs.
Crustacea: Species include crab, crayfish, hard exoskeleton, compound eyes, two pairsof antennae, three pairs of mouthparts, abdomen has swimmerets (swimming legs),
Diplopoda: 2 or 1 pairs of legs per body segment attached to underside, 1 pair of antennae, slow moving, burrow/ inhabit small crevises, primarily detritivores, spiracles on underside of body.
Chilopoda: 1 pair per body segment attached to sides of the body, adapted for running, primarily carnivores, spiracles on the sides or top of body.
Insecta: Account for the vast majority of animal species on Earth, species include bees, ants, mosquitos, butterflys, segmented body composed of three tagmata, head, thorax and abdomen, compound eyes, antennae, three ocelli on the head, mouthparts, mandibles, one or two pairs of wings, three pairs of walking legs.
Crustacea: Species include crab, crayfish, hard exoskeleton, compound eyes, two pairsof antennae, three pairs of mouthparts, abdomen has swimmerets (swimming legs),
Diplopoda: 2 or 1 pairs of legs per body segment attached to underside, 1 pair of antennae, slow moving, burrow/ inhabit small crevises, primarily detritivores, spiracles on underside of body.
Chilopoda: 1 pair per body segment attached to sides of the body, adapted for running, primarily carnivores, spiracles on the sides or top of body.