Joint-Legged Animals 465/8 By: Amina Nur
Feb 24, 2016
Joint-Legged Animals 465/8
By: Amina Nur
Animals With Exoskeletons(Phylum Arthropoda)
In terms of numbers, Arthropods dominate animal life
9 000 000 arthropods are estimated to be undiscovered
All have segmented bodies, suggesting evolution from segmented Annelid Worms
Segments become more specialized in higher Arthropods, nearly all segments differ in function
They developed exoskeletons, joint legs and a hemocoel (blood cavity)
Exoskeleton is a thick external covering composed of strong waterproof carbohydrate molecules called Chitin
Protects animal, resists desiccation (drying out) in non aquatic environments, allowing them on land
Rigidity prevents efficient locomotion
Evolved appendages and groups of muscles which evolved into joints increasing mobility
No longer needed coelom to provide body shape Reduced ability for gas exchanged. Aquatic
arthropods developed gills that took in O2 and expelled CO2
Many arthropods evolved Tracheae to carry O2 to body
Rigidity hindered growth, they shed exoskeleton when they grew and replaced them with a bigger one (adapted by moulting)
Circulatory system has a hemocoel Over time their bodies replaced body fluid with
blood which travelled through vessels and emitted into hemocoel
It bathed organs directly in an arrangement called Open Circulatory system
Developed sensory receptors: eyes and antennae
Segments of exoskeleton modified in different arthropod groups. Specialized regions, modified, joint appendages, and groups of muscles improved arthropod function and mobility.
Class Arachnida
Includes: Scorpions, spiders, mites and ticks
Body has 2 parts: head fusing to body segments forming cephalothorax
Posterior body segments (abdomen) contain most organs
Arachnids have 6 pairs of appendages – each for different functions:(1) To feed(2) Sense environment(3) The last 4 are used to walk
Reproduction: Male inserts sperm into small sac in the
female called the seminal receptacle where fertilization occurs
Life cycle: Miniature adults hatch from eggs and live
independently from the time they hatch Gas exchanges through book lungs
(highly folded membranes) in abdomen Silk glands in spiders’ abdomen produce
protein threads for spinning webs
Many spiders build webs with their silk, but some use their long threads to mate or protect young
Class Crustacea
40, 000 species 3 Regions make up body:
Head Thorax Abdomen
Exoskeleton forms thick carapace (covers head + other segments)
2 appendages, antennae, followed by the mandibles
Mandibles crush food and feed it to the mouth
Behind mandibles, a pair of millipedes – sense environment, search for food
Behind that, large claw like Chelipeds grab food and protect themselves from predators
Four legs follow the Chelipeds On the abdomen, 6 pairs of swimmerets
help crustacean swim
Pair of flat appendages (Uropod) lie on tail (Telson) behind posterior end of abdomen
These act as paddles, moving the animal backwards
They have many gills, connected to walking legs, which is protected by Carapace
Gils are feathered to increase gas exchange surface area
Gases in water diffuse into and out of the gills and travel through the circulatory system to body tissues
To increase diffusion through blood vessels of gills, swimmerets on telson beat and sweep water forward, under carapace and over the gills.
Males and females come together to copulate
Class Insecta
Numerous of all animals species + 1.5 million species Insect bodies are like those of a crustacean On their heads one antenna senses the
environment On the thorax, there are 3 pairs of legs Gas exchanged carried out through air sacs
and tubes (trachea) Adults of flying insects, usually have two pairs
of stiff membranous wings attached to the thorax
Flies have only one. In beetles, front wings form hardened wing covers
Separate sexes to produce egg and sperm Some insects undergo simple development,
hatching like miniature adults Winged insect undergo complex developments Body structure changes radically in process of
metamorphosis – change of shape and diet
Transform from worm-like larva maturing through each instar, or early stages into adults
Diet change minimizes the competition for food between larvae and adults
This increase species’ chances for survival
Class Diplopods and Chilopods
Diploids millipedes Millipede suggest the insect has thousands
of feet Members of this class only have about a
hundred pair of legs Number of segments in the body range
from 10 – 100 Each segment has 2 pairs of feet (Diplopod
means ‘double footed’) Chilopods are known as centipedes Like Diplopods, Chilopods only have about
10 – 100 pairs of legs Each segment contains only one pair
Chilopods:
Diplopods:
Joint-Legged AnimalsBy: Amina Nur
Biology sucks…we all know nobody was really listening…