7- Les Ecdysozoaires

Ecdysozoaires

• Group of protostome animals characterized by ecdysis (molting)
• Include several phyla (e.g., Arthropoda, Nematoda)

Caractères dérivés (derived characteristics)

• Chitinous cuticle, three-layered: epicuticle, exocuticle, endocuticle
• Epicuticle secreted by microvilli of the epidermis
• Loss of locomotory cilia from epidermal cells
• Molting
• Terminal mouth position

Organisation schématique du tégument des Arthropodes

• Sensory seta (sensilla)
• Nerve fiber
• Epithelial cell
• Tormogen cell
• Nerve cell
• Glandular pore
• Cuticular spine
• Epicuticle
• Exocuticle
• Endocuticle
• Canalicular cell
• Nucleus
• Glandular cell

Nématodes

• Free-living or parasitic
• Body shape: threadlike, circular cross-section
• Thick cuticle, mostly collagenous
• Blastocoel cavity
• Longitudinal muscles only
• Ectodermal origin of nerve cords
• Cloaca
• Flagella-less sperm

Caractères généraux des Nématodes

• Fusiform body, tapered at both ends, often white
• Free-living or parasitic, ubiquitous
• Mouth surrounded by 3 to 6 lips
• Separate sexes
• Internal fertilization
• Direct development

Embranchement des Nématodes

• Approximately 25,000 species
• Include Platyhelminthes, Gastrotrichs, etc,
• Diverse group encompassing several other phyla

Ascaris

• Male and female anatomy depicted
• Diagram showing internal organs
• Mouth, esophagus, dorsal muscular chamber, ventral muscular chamber, intestine, rectum, anus

Systèmes excréteurs

• Tubular with rennet cells
• Basic-epithelial nervous systems
• Amphids, rings of sensory structures around mouth
• Separate sexes; direct development
• Constant number of cells and cell lineages per species (eutely)

Embranchement des Nématomorphes

• Extremely slender and long
• Larval stage is always parasitic on arthropods
• Atrophied or absent digestive system in adults
• Separate sexes; internal fertilization; metamorphosis
• Examples include Gordius aquaticus

Panarthropodes

• Segmented bodies with a hard exoskeleton
• Paired, non-fused appendages, often ending in claws
• Food intake via modified anterior appendages
• Dorsal vessel with lateral ostia
• Open circulatory system (hemocoel)
• Complex brain (protocerebro, 1 or 2 ganglions, tritocerebro)

Embranchement des Onychophores

• ~165 species
• Terrestrial
• One pair of lobopods per segment

Tardigrades

• Microscopic, aquatic, or terrestrial environments
• Four pairs of short, unjointed legs with claws
• Thin cuticle, often with scales, tubercles (hairs)
• Buccal stylets
• Separate sexes; direct development
• Cryptobiosis (extreme dormancy)
• Encystment (formation of protective cysts)

Testez vos connaissances sur les écdysozoaires, un groupe d'animaux protostomiens, et les nématodes, avec leurs caractéristiques dérivées et structures. Ce quiz couvre les détails importants de leur morphologie et organisation. Préparez-vous à approfondir votre compréhension de ces phylums essentiels !