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Zoology, lecture 12

Invertebrates: Arthropoda

Crustaceans Subphylum of arthropods that includes crabs and lobsters
Chelicerans Subphylum of arthropods that includes spiders and scorpions
Uniramus Subphylum of arthropods that includes insects and centipedes (they have unbranched appendages)
Cephalothorax Fused middle section in certain crustaceans that contains the gills
Copepods A group of small crustaceans in marine and freshwater environments (some planktonic, some benthic)
Problem with the exoskeleton Prevents continuous growth
Solution to the continuous growth problem of the exoskeleton in arthropods Molting--shedding of the exoskeleton and growth of a new one.
Arthropod life cycle As a result of the molting and exoskeleton, they have multiple life cycles allowing for fixing physical damage and production of stages that occupy different niches.
Full life cycle Intermediate stage of pupa גולם
רסח life cycle No intermediate stage of pupa.
Number of moltings between birth and maturity Varies among groups and species. In most cases there is no more molting once they have reached maturity (when they are ready for reproduction).
Benefit of the arthropod structure It is a model that allows for all kinds of variation--flexibility in the number of segments,
Segmented appendage הקורפ ףג A muscular protrusion covered in a hard exoskeleton made of segments with segmented muscles inside allowing for complex motion.
Origin of segmented appendages in arthropoda They appear to have originated from the parapodia in polychaetes of the phylum annelida. Some people disagree.
Different kinds of appendages in arthropoda All variations of on model. Claws, legs, antennae, sensory appendages, jaws etc.
Three main body segment types: Head and body (like the centipedes) Cephalothorax+stomach (like lobsters) and head, chest, stomach (ants etc.)
Skeletal changes that came with the production of the exoskeleton Loss of the turgor (hydrostatic) skeleton that was present in annelida (based on coelomic sacs) so the septa disappeared.
Circulatory system changes that came with arthropoda The annelida closed circulatory system disappeared. The dorsal vessel acts as a pump (heart) and the blood mixes with the coelomic fluid (lympha)
Haemolympha Liquid that is a mix between lympha and blood that results when the septa of the coelomic sacs disappear.
Disappearance of the closed circulatory system The mixing of the blood/lympha allowed for direct transfer of waste/nutrients through the body cavity. No need anymore for tubes.
Haemocoel The new cavity produced when the blood mixes with the lympha.
Comparison between open/closed blood systems Closed has a branched set of closed tubes in each segment through which diffusion takes place. In the open system there is pumping by the dorsal heart with an open tube that returns the liquid to the front of the body.
Nephridia in the arthropoda (marine) Fusion of the segments allowed for one set of nephridia to serve the entire body cavity. Labyrinth cleans it out, urine is stored in the bladder and removed. In crabs there are two bladders at the head.
Nephridia in insects (land creatures) They often live in very dry areas so instead of releasing their waste out of their body they release it into their digestive system where the water component is reabsorbed and just the solid waste is removed.
Malpighian tubes Tubes that are closed on the end in the haeomocoel. They are responsible for bringing the haemolymph through the digestive system from where it is released as uric acid.
Arthropoda Reproductive system Not segmented.
Arthropoda Nervous system Primitive representatives have the ladder structure, ganglia chain (characteristic of annelida) is present in many arthropoda (butterfly larvae, etc), developed cerebral ganglia is characteristic of insects, fusion of most ganglia (some insects), or all.
Nervous system consideration The more compact the system, the more complex the system function.
Arthropod Respiration Aquatic species breath using gills, (crabs, waterborn instects) Gas exchange is performed through the body surface and oxygen is distributed through the haemolymph (CO2 is removed)
Gills Protrusions of the body wall with increased surface area allowing for efficient gas exchange
Blood flow in an open system There is a covering over the body wall with a gill chamber filled with water used in respiration. They can function as if they were still in the water cause they carry the water with them.
Some arthropoda still require a moist environment (Like spiders) and they breath using a pair of book lungs
Book lungs Found in certain arthropods, they are an inward protrusion of the body wall composed of a series of lamellae. The air fills the pockets and the haemolymph on the other side absorbs oxygen through diffusion.
Dryland Arthropod Respiration (uniramus are purely land creatures) They developed a system of tracheas that sink in and branch all the way to tracheolae that reach the tissues.
Vertebrate vs. invertebrate respiratory organs In vertebrates all respiratory organs developed as a protrusion from the digestive system whereas in invertebrates it was as a protrusion of the body wall.
Trachaeoli in insects They are branches of the respiratory system that are one way passages all the way to the tissues. Intake is often through holes in the body wall.
Difference between lungs/gills and tracheolae W/lungs and gills the gas exchange is mediated by haemolympha whereas with trachaeoli the branches go straight to the tissues with no mediation.
Nephridia system among land-dwelling arthropods in moist environments Coxal glands absorb haemolympha that then goes through a series of twisted tubes for reabsorption of crucial components. Waste reaches a bladder where it is released from the body through a hole near the rear appendages.
Pure land dwellers excretory system They use malpighian tubes that empty into the digestive system so ensure reabsorption of any extra water and release of uric acid (preservation of water)
Crustacean characteristics Most varied group of arthropoda, marine/freshwater, less on land. Important in the water like insects are on land, Biramos (two branches on their appendages).
Trilobita characteristics Subphylum that disappeared 300 mya, varied marine group (4000) species) with a dorso-ventrally flat body separated into 3 lobes (central and side) no oral appendages, looks segmented from the outside, compound eyes, legs are double branched, rest single.
Chelicerata characteristics םיינשיבכעה Marine origin (now mostly land) Two body segments (cephalathorax and abdomen) no preoral appendages, 6 pairs of limbs on the c.th. (2 pinchers, 2 sensory, 4 pairs of legs) stomach has limbs (or remains) fused plates on stomach.
Malacostraca Class of modern םינטרס
Branchiopoda Class of lower םינטרס
Created by: YaelNoa