Phylum Annelida true coelom present (segmented worms, bristle worms) mesoderm on inside of body wall and outside 15,000 species of digestive system layers of muscles inside body wall and on outside of large successful phylum in water & on land digestive tract include earthworms, sand worms, bristle worms, clam worms, fan worms, leeches with head-body-pygidium some with bizzare forms worldwide distribution: head (prostomium & peristomium) marine, brackish, freshwater and terrestrial most annelids show some degree of Body Form cephalization with a distinct head (=prostomium) elongated wormlike body tentacles, palps and sensory structures <1mm to 3 meters peristomium behind prostomium contains the hollow tube-within-a-tube design mouth one of the most successful animal designs with pharynx and chitinous jaws à room for development of complex organs body with well developed metamerism with muscle layers (=segmentation) à allows for circulation of body fluids most prominent distinguishing feature à provides hydrostatic skeleton seen in just a few other phyla: eg arthropods, chordates segments are separated by tissue = septae Animals: Phuylum Annelida; Ziser Lecture Notes, 2015.10 1 Animals: Phuylum Annelida; Ziser Lecture Notes, 2015.10 2 epidermis a single layer of cells (columnar epithelium) each segment has it’s own set of muscles and other organs epidermis secretes a thin flexible protective cuticle allows more efficient hydrostatic skeleton for most annelids have setae à small chitinous bristles burrowing and movement secreted by epidermis offers a way to achieve greater size: repeated on each segment (ie. “bristle worms”) rather than increasing size of each organ used as anchors while burrowing à each organ is repeated in each segment to prevent capture allows organs of each segment to become more specialized for various functions such as some used for swimming digestion, respiration, reproduction, locomotion, etc or as protection or camoflage the segmentation is both external and internal beneath epidermis is two layers of muscle tissue essential features of segmentation: thin layer of circular muscle several systems (eg. nervous, excretory) show serial repetition thick layer of longitudinal muscle (obliquely striated) segmentation is produced during embryonic development enhances use of hydrostatic skeleton NOT the same as asexual budding as in tapeworms allows for peristaltic movement for digging terminal pygidium with anus through sediment Body Wall body cavity a true coelom Animals: Phuylum Annelida; Ziser Lecture Notes, 2015.10 3 Animals: Phuylum Annelida; Ziser Lecture Notes, 2015.10 4 lined with peritoneum (squamous epithelium) across surface lines inside of body wall & outside of digestive 3. swimming: tract mainly polychaetes and leeches also layers of muscle along digestive tract undulating body movements peritoneum also form mesenteries that hold blood vessels and the septae between parapodia help in polychaetes segments Feeding & Digestion Movement complete digestive tract “tube within a tube” design coelom is filled with fluid (except leeches) which serves as hydrostatic skeleton muscle layers allow modification of tract into various structures: annelids have 3 general types of movements: muscular pharynx- to take in food, often with 1. burrowing: eversible pharynx with jaws waves of peristaltic contractions sweep crop – food storage down body gizzard – food grinding 1st animal elongates àcontraction of circular muscle 2nd animal sortens à contraction of longitudinal muscle intestine – digestion and absorption of nutrients setae anchor hind end of body while front end pushes foreward anus – elimination of undigested wastes 2. crawling: Respiration polychaetes use parapodia alternately to move through body wall in most species Animals: Phuylum Annelida; Ziser Lecture Notes, 2015.10 5 Animals: Phuylum Annelida; Ziser Lecture Notes, 2015.10 6 oxygen: body wall is richly supplied with capillaries to hemoglobin (Fe) red - most annelids absorb and transport oxygen hemerythrin (Fe) red chlorocruorin (Fe) green some marine forms respire through parapodia (only 4 blood pigments known in animal kingdom & annelids have 3 of them) a few species have gills blood also contains amoeboid cells which engulf Circulation foreign particles (like our WBC’s) body cavity is filled with coelomic fluid which helps annelids therefore have a double transport system for move food and wastes around foods, gasses, wastes most annelids also have a closed circulatory system fluid filled coelom that more efficiently carries nutrients and wastes circulatory system with heart & vessels several pairs of “pumping hearts” keep blood flowing à foods, wastes and respiratory gasses are carried both in blood and in coelomic fluid dorsal and ventral vessels connected by capillary network Nervous System dorsal vessel sends blood anteriorly have both CNS and PNS ventral vessel sends blood posteriorly CNS: a pair of dorsal cerebral ganglia above the dorsal vessel is main pump pharynx and ventral nerve cord several pairs of aortic arches (=”hearts”) help to with paired fused ganglia in each segment keep pressure up in ventral vessel PNS: nerves branch off fused ganglia to supply blood: body wall and body organs most with dissolved blood pigments to carry Animals: Phuylum Annelida; Ziser Lecture Notes, 2015.10 7 Animals: Phuylum Annelida; Ziser Lecture Notes, 2015.10 8 Senses: secondary sex characteristics simple single celled photoreceptors or clusters of regeneration cells ocelli (= eyespots) Excretion a few polychaete eyes have cornea, lens, retina one pair of nephrida (=metanephridia) in each à can form images segment similar to that in molluscs (a few polychaetes have protonephridia or both) statocysts in some for balance nephric tubule: nuchal organ à ciliated pit in head area nephrostome = funnel like opening into previous segment also found in some molluscs and a few other invertebrates coiled ciliated tubule surrounded by capillaries may function in chemoreception bladder like structure tentacles & palps à well developed sense of nephridipore = opening to outside touch function: other simple chemoreceptors wastes from coelom are drawn in free nerve endings à tactile?? salts and organic wastes from blood are discharged into duct Endocrine System useful stuff is selectively reabsorbed neurosecretory cells in brain and ganglia in earthworms and leeches chlroagogue cells secrete hormones that regulate: collect NH4 or urea and deposit in blood or take directly to nephrostome reproduction Animals: Phuylum Annelida; Ziser Lecture Notes, 2015.10 9 Animals: Phuylum Annelida; Ziser Lecture Notes, 2015.10 10 some nitrogen wastes are also excreted through body distinct head with eyes and tentacles wall segments with parapodia and lots of setae excretory organs also help in salt and water balance no clitellum Reproduction and Development Class: Clitellata (Earthworms & Leeches) Annelids have both asexual and sexual reproduction subclass: Oligochaeta (Earthworms) mainly terrestrial and freshwater quite variable within the phylum head absent Asexual fewer setae, no parapodia most can bud to some degree subclass: Branchiobdellida commensal on crayfish other spontaneously fragment no setae Sexual posterior sucker only monoecious or dioecious subclass: Hirudinea (Leeches) most annelids are hermaphrodites terrestrial, freshwater or marine larva, if present = trochophore no parapodia or setae fixed # of segments with “false segments” (=annuli) Classification of Annelida anterior and posterior suckers Class: Polychaeta (Bristle Worms) Class: Echiura (Spoon Worms) mostly marine shallow marine burrowing forms Animals: Phuylum Annelida; Ziser Lecture Notes, 2015.10 11 Animals: Phuylum Annelida; Ziser Lecture Notes, 2015.10 12 once considered a separate phylum Class: Polychaeta (Sand Worms) means “many setae”; also called bristle worms 10,000 species; 2/3rds of all Annelid species sand worms, bristle worms, fan worms, clam worms, etc largest, most diverse and most primitive class of Annelids all are aquatic; mostly marine; worldwide distribution a few found in freshwater most 2-4” long (5-10 cm) ; some up to 10’ (3 M) often brightly colored deposit feeders, filter feeders, predators, scavengers, live in crevasses, old shells, burrows or construct tubes some have elaborate filtering structures eg feather duster worms a few are pelagic à part of the plankton Animals: Phuylum Annelida; Ziser Lecture Notes, 2015.10 13 Animals: Phuylum Annelida; Ziser Lecture Notes, 2015.10 14 both parapodia and setae are moved by internal important in marine food chains muscle bands these parapodia have a variety of functions and Body Plan create many bizzare shapes: distinct head with mouth and sense organs & à crawling or digging in the sediment; use parapodia as as legs wormlike body or trunk with repeating segments body segments with flaplike parapodia à swimming, use parapodia as paddles Head à as gills for respiration à used as anchors while burrowing or to prevent have distinct head capture à to create feeding currents inside tubes head has retractable pharynx with chitinous jaws used to capture prey à converted into feathery appendages to filter water lots of different kinds of sense organs à as protection or camoflage 1. chemoreceptors (nuchal glands) on palps and à in some, parapodia modified into fans and mucous tentacles bags for feeding or to create water currents 2. touch receptors also on tentacles for locating food and most polychaetes are active swimmers, crawlers or shelter