Trochozoa: Annelids (Polychaetes) Flashcards
Embryonic Development: Annelid Cleavage and Formation
Annelids: Spiral Cleavage forms Mesentoblast
What do annelids’ mesoderm form?
Coelom, mesenchyme, nephridia, muscle, skin cells
What is a trochophore?
Planktonic larva
Anterior vs Posterior cells/cilia of a Trochophore are
Anterior: Prototroch (beat down for propulsion
Posterior: Metatroch (beat up for swimming and trapping food particles)
Development of the Mesentoblast
Mesentoblast migrate and descendants proliferate in blastocoelic space; schizocoely
Mesentoblast goes through Teloblastic Growth; what is that?
Development of a series of pairs of coelomic spaces; shared in common with arthropods; newest segments are posterior in front of pygidium
Two parts of Annelid Head
Before mouth: Prostomium
Post mouth: Peristomium
What is the Pygidium?
Posterior part of trochophore; has mesodermal stem cells that give rise to segments but does not contain coeloms itself
What is the Cuticle?
Extracellular matrix secretions over the apical side of ectodermally derived epithelial cells
What are Parapodia
A characteristic of annelid body wall; the extension of the body wall and its connective tissue to make limbs (may be homologous to arthropod limbs
Parapodia epidermal cells secrete Chitinous Cuticles in 2 ways:
- Aciculae: internal skeletal rod of chitin for cuticular specialization
- Chaetae: diverse in form, rod shape secretions that have many functions
What forms the palps?
Extension of the prostomium
What form the tentacles?
Body wall extensions from the peristomium
What are septae?
Pair of epithelia perforated by the gut that separates segments
Blood Flow in Annelids
Tubular spaces from blastocoelic lining (posterior to anterior in major dorsal vessel)
Nerves in more Bilaterians
Masses of nerve cells (called Ganglia) make ventral nerve cord; anterior part splits around pharynx to form dorsal ganglionic masses
Sinusoidal Locomotion
Contract left and right longitudinal masses
Peristaltic Locomotion
Alternating contractions of either all longitudinal muscles or circular musculature in some segments (common in burrowers)
Protonephridia (1. Structure 2. How it works 3. Filtration)
- Invagination of epidermis grows in connective tissue layer to meet with nephridial cell
- Motion of flagella of flame cell allows the excretory system to push fluid to the excretory tubule
- Basal lamina as filtration surface (material goes through podocytes)
Metanephridia (1. What does it lose/ keep from protonephridia? 2. How does it pressurize fluid?)
Not via ciliary motion, no flame cell but has the collecting nephridial tubule
Musculature as pumping power (creates greater hydrostatic pressure through podocytes and basal lamina for better filtration)
What is a Nephrostome?
Nephrostome (opening into nephridial tubule and into next anterior coelomic space of following segment) - most often, gametes spawn out of tubule but sometimes spawn out of separate coelomiduct
What is an Epitoke?
Specialized segment of body generated by asexual budding or cloning and develop functional specializations for swimming and sexual reproduction
Lifestyles of the Wet and Slimy (Reproduction, Specialization, Structure)
Reproduction of parapodia and setae (burrowing)
Tagmatization of groups of segments
Perforation and loss of septae/segments
Skeletal elements: Heavy chitin, calcium carbonate, gelatinous mucous, sediment
Lifestyle of the Barely Damp
Reproduction of parapodia and setae
Tagmatization, perforation and loss of setae and segments
Lifestyle of Sedentary Annelids
Suspension feeders, elaborate head appendages (parapodia of peristomium into large structures with extenstions of BVS and fine branching, secrete mucous sheet and spits of balls of mucous called Radiole)
Sister Group to the rest of the Annelids:
Chaetopteridae
- specialized morphologies of polychaetes
- permanent burrow
- suspension feeders
- water current by parapodia, anterior parapodia secrete mucous for filtration to trap particles and ingest
