Lecture Notes 7: Annelida

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- grooved feeding palps – only in Canalipalpata; tend to be U shaped, with ciliated path in groove serving to transport food. Grooved palps dorsal and attached at prostomial-peristomial junction. Include paired spionid palps, multiple terebellid tentacles (arise from prostomium), radioles of sabellids, buccal tentacles (again multiple – e.g. Pectinariidae) Segments: each w/ own separate, paired coelomic compartments; separated by septa & mesenteries. Body wall: Cuticle (collagenous, may contain scleroprotein), Epidermis, circular, longitudinal muscle, peritoneum. Circular muscle as sheet, long muscle in 4 bands in almost all (Rouse & Fauchald 1997) Parapodia: Notopodium, neuropodium, if loose one always loose notopodium. Nereid type advanced, primitively low, brasing structures, without aciculas, little musculature, noto- and neuropodia separate. In evolution may become more muscular and gain aciculae (in Aciculata) and gain strong intrinsic musculature for chaetae & whole paddle; for swimming, etc. Or reduced to chaetae only (clitellates). Dorsal and ventral cirri – fleshy extensions; funky chaetae – aphroditids; scale of polynoids; specialized gills Parapodial muscles evolve from circular musculature Dorsal and ventral cirrus – outgrowths of body wall – mainly in Aciculata Aciculae – in Aciculata only. Fully internalized chaetae, with strong muscles that help support and move large parapodia. Neuropodia have it, notopodial aciculae also in many Eunicida and Phyllodocida Neuropodia reduced to low welts = tori in many Scolecida & Canalipalpata Chaetae: Chitinous, produced by chaetoblasts, has dynamic microvilli w/ start & stop activities, make complex morphologies as a result. Variety of chaetal types, hooks, capillaries, uncini, compound. Chitin restricted to protostomes. Setae - term for arthropod cuticle-coated structure w/ core of cells -- chaetae solid, secreted str.s. Body cavity: Coelom, lined by peritoneum; prd. cavities in each segment, each of independent schizocoelous origin; no coelom in unsegments. Peritoneum surrounds guts, blood vessels & nerves in middle in retroperitoneal spaces. Septa = double peritoneum. Excretory organs & gonads associated w/ coelom. Advantages include greater possibilities for locomotion, localization of injuries. Some polychaetes loose septa between some segments and create larger, confluent coelomic spaces. Some (especially small, interstitial worms) loose segmentation and coelom altogether. Locomotion: Circular & long. muscles together w/ hydrostatic skeleton for peristaltic locomotion - a segment at a time. A major advantage of segmentation, is in locomotion: localized coelomic fluid, together with local contraction of segmental muscles, allows the local widening or elongation of segments. Septa - give local control of movement. Peristaltic wave like this passing down animal, allowing burrowing motion, crawling motion. Also undulatory swimming, paddling w/ parapodia, both by alternate contractions of longitudinal muscles. Several groups with large pharynxes lose septa at anterior end of their body and use large, resulting coelomic cavity to power eversion of their pharynx – e.g. glycerids Circ.: Both by coelom and by BVS. Most w/ closed BVS. Vessels of blastocoel, myoepithelial, their contraction drives blood through bug. Dorsal vessel to head; ventral vessel to tail; dorsal especially contractile. Blood vessels to gills -- respiration; to nephridial canal -- resorption. Variety of blood pigments: hemoglobin, chlorocruorin (Fe), hemerythrin (Fe). Circulatory system lost in some, e.g. "blood worms", glycerids, also capitellids, some terebellids – some loose septa as well (e.g. to house proboscis in glycerids) so coelom takes over circulation and can hold blood pigments (hence name).
Resp.: Varied gill structures, though absent in small or narrow bugs; SA/V issues. Gills probably evolved many times. Extensions of body wall, w/ or w/o coelom, usually in association w/ parapodia, usually heavily vascularized. w/ parapodia: arenicolids - bushy, cirratulids - threads separate: terebellids - on dorsum of ant. segments. chamber: polynoids & aphroditids feeding appendages: sabellids, serpulids, spionids, etc Resp. movements - may irrigate burrows Excr.: Paired nephridia / sgm in polychaetes = segmental organs. - separate gonoduct and metanephridium – e.g. Capitellidae - separate funnels for gono- and nephr., but become confluent so one exit – e.g. Hesionidae - single main duct with nephrostome head for gametes + protonephridial head – e.g. Phyllodocidae - single funnel system serves all – most families - single funnel used for excretion; gametes exit through rupture of body wall – e.g., Nereididae Dig.: Tripartite - stomodaeum, midgut, proctodaeum. Stomodaeum may include eversible pharynx, either axial, all-around eversible, all ventral eversible pad; often w/ jaws. Cuticle lining of stomodaeum can form jaws – many Eunicida and Phyllodocida Ventral, eversible pad pharynx = ventral buccal organ & ventral muscular proboscis of Rouse & Pleijel (2001) – only ventral part of pharynx everted. Axial pharynx = simple axial proboscis and muscular axial proboscis of R&P - all around eversible Midgut - ant. portion secretes dig. enzymes; undifferentiated in errants, differentiated in sedentaries into esoph., flat stomach (dig. enzymes), thinner intestine - absorption. Salivary glands may occur. Proctodaeum -- rectum, for fecal pellet fm., anus terminal, usually slightly dorsal on pygidium. Nerv.: Brain in prostomium at least in part, though may penetrate back up to 5th/6th sgm. though even then within prostomial space (septa bent to make room for it); never truly prd. as not segmental str., primitively not prd.. Circumesophageal ring in peristomiumto subesophageal ganglion in peristomium + 1-5 sgm? Though some segmental ganglia may be moved up even into posterior end of brain. Ventral nerve cord prim. prd., may become fused. Single or prd. ganglia per segment (sometimes only remnants of segmentation). Giant fibers - 1-5 prs. used for startle response in some sedentaries. Sens.: General sensory cells over body, esp. dorsal cirri. - Proprioceptors - respond to deformation or stress: 1) parapodial stretch receptors, 2) notopodial flap receptors, 3) dorsal cirri receptors, 4) chaetae receptors. - Statocysts in some, often w/ sandgrains, some make own lith, usually assoc. w/ ant. parapodia. - Chemoreceptors - nuchal organs - 1 pr. at line between pro- and peristomium, ciliated sensory cells (+ciliated supportive cells) covered by bizarre waxy cuticle. - Photoreceptors as simple eye spots, only 2 cell / ocellus to great alciopid eyes, which can judge distance in open water (stereoptical). Some eyes can form images. Few eyes ciliary, most rhabdomeric. Eyes on brachioles of sabellids – shadow response (w/ giant nerve) - Antennae, palps Repr.: Asexual reproduction common. - budding as clonal propagation. Syllids can have either axial or lateral budding. Dodecaceria breaks up; single segments will form whole worm – build large “colonies” really clonal aggregations with confluent tubes, but separate bodies.
Page 1: Scolecida - Echiura Clitellata - Ol
Page 5 and 6: - palps antenniform, + 1-3 antennae
Page 7: Dorso-ventrally flattened; Ant. and

Lecture Notes 7: Annelida

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