annelids. phylum annelida – “little ring” – segmented body round worm-like animal that has a...

Annelids

Annelids

• Phylum Annelida – “little ring” – segmented body• Round worm-like animal that has a long, segmented

body• Sizes range from .5mm to 3m• True coelom lined with mesoderm• “tube-within-a-tube” digestive tract – mouth to anus• Segments separated by internal walls celled septa. Most

segments are identical, some modified

Anatomy of an EarthwormAnus

Clitellum

Circular muscle

Longitudinalmuscle

Nephridia Ganglia Ringvessels

Reproductiveorgans

Ventralblood vessel

Ganglion

Brain

Mouth

Dorsalblood vessel

CropGizzardBody segments

Setae

Anatomy of an Earthworm

Feeding in Annelids

• Filter feeders to predators• Pharynx – very muscular, may be armed

with jaws (predators and herbivores), may be sticky (mucus, detritus feeders), act like a pump (deposit feeders and parasites)

• Mucus bag – filter feeders• Feather-like structures – filter feeders• Pharynx – esophagus – crop (storage) –

gizzard (ground up) – intestine

Circulation in Annelids

• Closed circulatory system – blood contained within blood vessels

• Blood moves toward the head (dorsal vessel)• Blood moves away from the head (ventral

vessel)• Ring vessels in each segment connect dorsal to

ventral vessels• Vessels act as “hearts” which help pump blood

through the system

Respiration in Annelids

• Gills – aquatic

• Skin – must stay moist, secrete cuticle (earthworm)

Excretion in Annelids

• Solid wastes pass through the anus

• Waste from cellular metabolism eliminated by nephridia

Response in Annelids

• Brain and several nerve cords• Ventral nerve runs entire length of body• Sense organs most often found in polychaetes

– True eyes that see shapes, Statocysts, chemical receptors, sensory tentacles, vibration sensors

• Defense, runaway and hide, a few fight with jaws (sandworm)– Marine fireworms have irritating bristles

Movement in Annelids

• Muscles– Longitudinal – lengthwise – make worm

longer and shorter– Circular – make worm fatter and skinnier

Reproduction in Annelids

• Most reproduce sexually

• External (broadcast) spawners – worms swarm to surface to spawn by millions

• Some hermaphrodites – exchange sperm; clitellum secretes mucus ring containing eggs and sperm which forms cocoon (earthworm)

Groups of Annelids

• Three classes of Annelids– Class Oligochaete– Class Polychaete– Class Hirudinea

Class Oligochaetes

• Few “bristles” – few setae

• Earthworms and tubifex worms

• Deposit feeders, eat dirt and produce “castings” – aerate and fertilize the soil

• Tropical earthworms produce castings 18cm long and 2cm in diameter

• Soil or freshwater

Examples of Class Oligochaetes

Class Polychaetes

• Many “bristles”

• Paired, paddle-like, appendages tipped with bristles (setae) (sea mouse)

• Live in all sorts of marine habitats

• Some free-living, some tube-builders

• May be brightly colored, iridescent, or luminescent

Examples of Class Polychaetes

Class Hirudinea

• Most parasitic, some carnivorous, most freshwater

• 6cm to 30cm long, two suckers, one at each end

• Penetrate skin by use of proboscis or sharp jaws

• Produce secretions that prevent clotting and anesthetizes wound

• Can swallow ten times its weight

Examples of Class Hirudinea

Comparing Flatworms, Roundworms, and AnnelidsComparing Flatworms, Roundworms, and Annelids

CHARACTERISTIC

Shape

Segmentation

Body cavity

Digestion and excretion

Respiration

CHARACTERISTIC

Shape

Segmentation

Body cavity

Digestion and excretion

Respiration

FLATWORMS

Flattened

No

Acoelomate

Gastrovascular cavity with one opening only; flame cells remove metabolic wastes

Through skin; no respiratory organs

FLATWORMS

Flattened

No

Acoelomate

Gastrovascular cavity with one opening only; flame cells remove metabolic wastes


ROUNDWORMS

Cylindrical with tapering ends

No

Pseudocoelomate

Tube-within-a-tube digestive tract; opening at each end; metabolic wastes excreted through body wall


ROUNDWORMS


No

Pseudocoelomate

Tube-within-a-tube digestive tract; opening at each end; metabolic wastes excreted through body wall


ANNELIDS


Yes

Coelomate

Tube-within-a-tube digestive tract; opening at each end; nephridia remove metabolic wastes

Through skin; aquatic annelids breathe through gills

ANNELIDS


Yes

Coelomate

Tube-within-a-tube digestive tract; opening at each end; nephridia remove metabolic wastes

Through skin; aquatic annelids breathe through gills

Comparing Flatworms, Roundworms, and Annelids (Continued)Comparing Flatworms, Roundworms, and Annelids (Continued)

CHARACTERISTIC

Circulation

Response

Movement

Reproduction

CHARACTERISTIC

Circulation

Response

Movement

Reproduction

FLATWORMS

No heart, blood vessels,or blood

Simple brain; nerve cords run length of body; eyespot and other specialized cells that detect stimuli

Gliding, twisting,and turning

Sexual (hermaphrodites); asexual (fission)

FLATWORMS


Simple brain; nerve cords run length of body; eyespot and other specialized cells that detect stimuli

Gliding, twisting,and turning

Sexual (hermaphrodites); asexual (fission)

ROUNDWORMS


Several ganglia in head region; nerve cords run length of body; several types of sense organs

Thrashing

Sexual (primary males and females)

ROUNDWORMS


Several ganglia in head region; nerve cords run length of body; several types of sense organs

Thrashing

Sexual (primary males and females)

ANNELIDS

Blood circulated through blood vessels in closed circulatory system

Well-developed nervous system with brain and several nerve cords; many sense organs

Forward peristaltic movement

Sexual (some are hermaphrodites; some have separate sexes)

ANNELIDS

Blood circulated through blood vessels in closed circulatory system

Well-developed nervous system with brain and several nerve cords; many sense organs

Forward peristaltic movement

Sexual (some are hermaphrodites; some have separate sexes)

Mollusks

Phylum Mollusca

• Phylum Mollusca– 100,000 species– Most share trocophor larval stage (free-

swimming larval stage)– Defined as soft-bodied animals that have an

internal or external shell

Anatomy of a Clam

Mouth

Shell

Stomach CoelomHeart

Nephridium

Adductor muscle

Anus

Excurrentsiphon

Incurrentsiphon

Gills

Mantle cavity

Foot

Intestine

Mantle cavity

Adductormuscle

Form and Function in Mollusks

• Body Plan – four parts: mantle, foot, shell, visceral mass– Mantle – thin layer of tissue that covers most

of the mollusk body – contains shell glands– Foot – movement, mouth, and associated

feeding structures– Shell – protection– Visceral mass – contains all organs

The Mollusk Body Plan

Shell

Mantle cavity

Foot

Gills

Digestive tract

Snail

Earlymollusk

Clam

Squid

Feeding in Mollusks

• Herbivores, carnivores, or filter feeders• Radula – found in snails and slugs – rasp-like

tongue– Herbivores scrape food– Predators drill shells or “dart” food

• Cephalopods – beaks• Clams, oysters, scallops – filter feeders use gills• Octopi use siphon (tube-like structure) to trap

plankton

Respiration in Mollusks

• Gills in mantle cavity in aquatic species

• Modified mantle in terrestrial species

Circulation in Mollusks

• Open circulatory system – blood flows through vessels and “sinuses” (open spaces) (clams and snails)

• Closed circulatory system – blood always flows inside vessels (cephalopods)

Excretion in Mollusks

• Remove ammonia with use of tube-shaped organs called nephridia

Response in Mollusks

• Simple to very complex nervous systems (scallops, octopi)

• Cephalopods, highly evolved eyes and brains

Movement in Mollusks

• Mucus in snails and slugs

• Jet propulsion in octopi

Reproduction in Mollusks

• In most mollusks, sexes are separate, broadcast spawners

• Cephalopods, internal fertilization

• Some gastropods are hermaphroditic

Groups of Mollusks

• Three classes of mollusks– Class Gastropoda– Class Bivalvia– Class Cephalopoda

Class Gastropoda

• “stomach foot”

• Snails, slugs, abalones, nudibranchs

• Some snails have operculum (hard disk on foot that forms a “door” when inside shell)

• Nudibranchs feed on cnidarians; utilize nematocysts for their own defense

• Bright colors mean bad taste or even poison

Examples of Class Gastropoda

Class Bivalvia

• “two shell”

• Clams, oysters, scallops

• Most are sessile– Epifaunal – on top of bottom (oyster, mussels)– Infaunal – in bottom (clams)

• Some are motile – scallops can move by flapping shells and have eyespots (Ocelli)

Scallop Swimming

Examples of Class Bivalvia

Class Cephalopoda

• “head foot”

• Squid, octopus, cuttlefish, nautilus

• Predators, beak for mouth

• Seem to be intelligent

• Move quickly via jet propulsion

• Little or no shell

• Highly developed eyes and brains

Examples of Class Cephalopoda

Ecology of Mollusks

• Fried calamari

• Shipworms

• aquaculture

Comparing the Three Major Groups of MollusksComparing the Three Major Groups of Mollusks

MOLLUSK GROUP

Gastropods

Bivalves

Cephalopods

MOLLUSK GROUP

Gastropods

Bivalves

Cephalopods

SHELL

Shell-less orsingle-shelled

Two shells held together by oneor two muscles

Internal shell orno shell

SHELL

Shell-less orsingle-shelled

Two shells held together by oneor two muscles

Internal shell orno shell

FOOT

Muscular foot located on ventral side and used for movement

Burrowing species have muscular foot. Surface-dwelling species have either no foot or a “reduced” foot.

Head is attached to a single foot. The foot is divided into tentacles or arms.

FOOT

Muscular foot located on ventral side and used for movement

Burrowing species have muscular foot. Surface-dwelling species have either no foot or a “reduced” foot.

Head is attached to a single foot. The foot is divided into tentacles or arms.

EXAMPLES

Snail, slug, sea hare, nudibranch

Clam, oyster, mussel, scallop

Octopus, squid, cuttlefish, nautilus

EXAMPLES

Snail, slug, sea hare, nudibranch

Clam, oyster, mussel, scallop

Octopus, squid, cuttlefish, nautilus

annelids. phylum annelida – “little ring” – segmented body round worm-like animal that has a...

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