Mollusca & Annelida

invertebrates protostomes Mollusca Annelida Porifera Metazoa ANCESTRAL PROTIST Ctenophora Metazoa Cnidaria Eumetazoa Acoela Single common animal ancestor Hemichordata Echinodermata True Tissues Deuterostomia Bilateria Chordata Bilateral & 3 germ layers Platyhelminthes invertebrates Rotifera Ectoprocta Figure 32.11 A phylogeny of living animals Lophotrochozoa Brachiopoda protostomes Mollusca Annelida Nematoda Ecdysozoa Arthropoda

Mollusca Body Plan Ceolomates (true coelum) 3 main body parts Often very reduced/small 3 main body parts Muscular foot (for movement) Visceral mass (w/ most internal organs) Mantle Creates calcium based shell mantle cavity in some (containing gills, anus, and pores) Shell in most Protection against predation & dessication

Mollusk organ systems Feeding & Digestive: Many feed with a rasp-like strap called the radula Herbivores or predators Filter feeders (using gills or “tentacles”) Beak (cephalopods) Complete digestive system w/ specialized organs Digestive gland (a.k.a. hepatopancrease) Cardiovascular: Open (except in cephalopods) Hemocyanin Excretory and osmoregulation Metanephridia

Mollusk organ systems Nervous: “brain” encircling pharynx Two ventral nerve cords (in most) Respiratory: Gills mantle Reproductive Most are dioecious w/ gonads in visceral mass Many gastropods are hermaphrodites Typically a ciliated larvae known as the trochophore

Generic Mollusc Body Plan Visceral mass Metanephridium Heart Coelom Intestine Digestive tract Gonads Mantle Mantle cavity Stomach Shell Mouth Radula Anus Gill Figure 33.15 The basic body plan of a mollusc Mouth Nerve cords Foot Esophagus Radula

radula

Four of the major classes of molluscs are Polyplacophora (chitons) Gastropoda (snails and slugs) Bivalvia (clams, oysters, and other bivalves) Cephalopoda (squids, octopuses, cuttlefish, and chambered nautiluses)

Polyplacaphora (Chitons) Figure 33.16 A chiton

Chitons Oval shaped body 8 dorsal plates Unsegmented body Foot acts as suction cup to hold in place (to prevent dislodgement and drying) Herbivores use radula to scrap algae off rocks Adaptation to intertidal zone

Gastropods (snails & slugs) A land snail Figure 33.17 Gastropods (b) A sea slug (nudibranch)

Gastropods ¾ of all mollusc species Move by rippling foot or cilia Shell, reduced, abscent Torsion Most are herbivores using radula to eat Some predator (radula bores holes or shreds prey) Many w/ eyes at tip of tentacles Aquatic  gills for gas exchange Terrestrial  lining of mantle in mantle cavity for gas exchange

Bivalvia (bivalves/ “shellfish”)

Bivalves All aquatic Dorsally hinged 2-part shell No distinct head Adductor muscle holds shell closed No distinct head Radula has been lost Some have eyes and sensory tentacles along the out edge of mantle Gill in mantel cavity Gill for filter feeding and gas exchange Most are suspension feeders Cilia move food in gills to mouth Incurrent siphon in, excurrent siphon out Many are sedentary Some fix themselves substrates, some move w/ feet

Figure 33.19 Coelom Hinge area Mantle Gut Heart Adductor muscle (one of two) Digestive gland Anus Mouth Excurrent siphon Figure 33.19 Anatomy of a clam Shell Palp Water flow Foot Mantle cavity Incurrent siphon Gonad Gill

Figure 33.20 Cephalopods Squid Octopus Chambered nautilus

Cephalopods: Octupus, squid, nautilus, cuttlefish marine predators Modified foot Tentacles (for prey capture) Excurrent siphon Beak (some with teeth) Radula reduced or vestigal Some poisonous Move with jet of water out excurrent siphon Shell is reduces and often internal (except nautilus) closed circulatory system Complex brain, eyes, and other sensory organs Well developed nervous system and senses (e.g., eyes & big brain)

Annelida: segmented worms Divided by septa internally Marine, freshwater, and damp soil (terrestrial) BODY PLAN Long, thin  worm Coelomates

Systems Closed cardiovascular system Complete digestive system w/ specialization Metanephridia Gills, parapodia, or surface gas exchange “brain” near pharynx Ventral nerve cord

polycheates > oligochaetes > hirudinae Historical Classes Polychaetes Oligochaeates Hirudinae Modern relationship: polycheates > oligochaetes > hirudinae

Polycheata: polycheates and tube worms Parapodia Figure 33.22 An errantian, the predator Nereimyra punctata

Polycheates Marine Mobile forms are: Parapodia w/ chaetae (“bristles”) Predators Herbivores (of large algae) Scavengers Parapodia w/ chaetae (“bristles”) Movement Can be vascular and used for gas exchange Well developed jaws and sensory organs

Polycheates: tube worms Filter feeders Gills or “tentacles”

Oligocheates Aquatic and terrestrial Setae Circular and longitudinal muscles Hydrostatic skeleton Peristalsis Gas exchange over surface Cross fertilizing hermaphrodites

Figure 33.25 Coelom Cuticle Epidermis Septum (partition between segments) Circular muscle Metanephridium Longitudinal muscle Dorsal vessel Anus Chaetae Intestine Skin Ventral vessel Fused nerve cords Nephrostome Clitellum Esophagus Figure 33.25 Anatomy of an earthworm, a sedentarian Metanephridium Pharynx Crop Intestine Giant Australian earthworm Cerebral ganglia Gizzard Mouth Subpharyngeal ganglion Ventral nerve cords Circulatory system vessels

Figure 33.25a Anus Skin Metanephridium Clitellum Esophagus Pharynx Crop Intestine Figure 33.25a Anatomy of an earthworm, a sedentarian (part 1: cutaway) Cerebral ganglia Gizzard Mouth Subpharyngeal ganglion Ventral nerve cords Circulatory system vessels

Figure 33.25b Cuticle Coelom Epidermis Circular muscle Septum (partition between segments) Longitudinal muscle Metanephridium Dorsal vessel Chaetae Intestine Figure 33.25b Anatomy of an earthworm, a sedentarian (part 2: cross section) Ventral vessel Nephrostome Fused nerve cords

Hirudinae Figure 33.24 A leech

Hirudinae (leeches) predators, scavengers, blood-sucking parasites Mostly freshwater Lack setae Dorso-ventrally flattened Suckers to hold prey Subtle segmentation Blood sucking type bladelike jaws aneasthetic saliva anticoagulant, hirudin Blood letting v. modern use

Circulatory Systems: open v. closed

Respiratory Structures

nephridiostome nephridiophore