Mollusca & Annelida

ANCESTRALPROTIST

Porifera

Ctenophora

Cnidaria

Acoela

True Tissues

Metazo

a

Eu

metazo

a

Bilateria

Hemichordata

Echinodermata

Chordata

Platyhelminthes

Rotifera

Ectoprocta

Brachiopoda

Mollusca

Annelida

Nematoda

Arthropoda

Deu

tero

stom

ia

Lo

ph

otro

cho

zoa

Ecd

ysozo

a

Single common animal ancestor

prot

osto

mes

inve

rteb

rate

s

Bilateral & 3 germ layers

Mollusca Body Plan

• Ceolomates (true coelum)– 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

Metanephridium HeartVisceral

mass

Coelom IntestineGonads

Mantle

Mantlecavity

Anus

Gill

Foot Nervecords

EsophagusMouth

Mouth

Radula

Radula

ShellStomach

Digestive tract

Generic Mollusc Body Plan

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)

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) A land snail

(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

– 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 33.19Mantle

Digestivegland

Hinge areaGut

Coelom

Heart Adductor muscle(one of two)

Anus

Excurrentsiphon

Waterflow

IncurrentsiphonGillGonad

Mantlecavity

Foot

Palp

Shell

Mouth

Figure 33.20Squid

Octopus

Chamberednautilus

Cephalopods

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

• Segmented• Divided by septa internally• Marine, freshwater, and damp soil (terrestrial)

BODY PLAN• Long, thin worm• Coelomates• Segmented

Systems

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

Historical Classes

• Polychaetes• Oligochaeates• Hirudinae

Modern relationship:polycheates > oligochaetes > hirudinae

Polycheata:polycheates and tube worms

Parapodia

Polycheates• Marine• Mobile forms are:– 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 33.25Epidermis Cuticle

Coelom

Septum (partitionbetween segments)

Metanephridium

Anus

Skin

Metanephridium

Intestine

Gizzard

Ventral nerve cordsCirculatory system vessels

Subpharyngealganglion

MouthCerebral ganglia

Pharynx

Giant Australian earthworm

EsophagusCrop

ClitellumNephrostome

Fusednerve cords

Ventral vessel

Intestine

Chaetae

Dorsalvessel

Longitudinal muscle

Circular muscle

Figure 33.25aAnus

Skin

Metanephridium

Intestine

Gizzard

Ventral nerve cordsCirculatory system vessels

Subpharyngealganglion

Mouth

Cerebral ganglia

PharynxEsophagus

Crop

Clitellum

Figure 33.25bEpidermis Cuticle Coelom

Septum (partitionbetween segments)

Metanephridium

Nephrostome Fusednerve cords

Ventral vessel

Intestine

Chaetae

Dorsalvessel

Longitudinal muscle

Circular muscle

Hirudinae

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