Week 5: Mollusks and Annelids

mollusk general characteristics

exoskeleton (shell), bilateral symmetry, unsegmented, complete digestive systems, radula (not all), moderately complex nervous system

radula

rasping tongue for feeding

open circulatory system

hemolymph replaces blood, not enclosed in vessels

closed circulatory system

blood enclosed in vessels, more efficient gas exchange

molluscan body plan

shell, foot, visceral mass, mantle

adaptive radiation

diversification of a group of organisms to fulfill different niches (mollusks are a good example bc they have a huge range of morphologies but a common ancestor)

Clade Gastropoda example

snails and slugs

Clade Gastropoda feeding

use radula

Clade Gastropoda symmetry

BILATERAL, appears asymmetrical due to torsion and coiling

torsion

the visceral mass is twisted during embryonic development, mantle cavity is on anterior end above the mouth, leads to foiling (butt is on head)

coiling

spiral winding of the shell (and visceral mass)

Clade Scaphopoda organism

tusk shells

Clade Bivalvia organism

clams

Clade Bivalvia feeding

no radula, suspension feeders (food trapped by mucus on gills)

clam: adductor muscles

CLOSE shell to protect body

clam: foot

movement

clam: gills

suspension feeding, gas exchange

clam: labial palps

secrete mucus onto gills

clam: mantle

secretes shell

clam: umbo

origin of shell

clam: visceral mass

soft portion of the body

clam: coelomic cavity

cavity lined with epithelium, arises from mesoderm, greatly reduced in mollusks

Clade Cephalopoda example

squid

squid predatory adaptations

convergently evolved eyes, intelligent, closed circulatory system

squid: mantle

fills with water when relaxed, expels water through siphon when contracted

squid: tentacles

two long, captures prey

squid: arms

8 short, bring food to mouth

squid: siphon

water expelled for propulsion

squid: eyes

convergently evolved

squid: pen

reduced shell, provides support

squid: gills

respiration

squid: ink sac

releases dark fluid when alarmed

Clade Polyplacophora

chitons, use radula

annelid general characteristics

closed circulatory system, hydrostatic skeleton, complete digestive tract, monoecious, longitudinal and circular muscles

metamerism

segmentation

setae

chitinous bristles for locomotion

annelid subgroup characterization

characterized by density of setae

"Polychaeta"

many setae, Nereis

polychaeta: parapodia

locomotion and respiration

polychaeta: setae

locomotion

polychaeta: eyes

advanced photoreception

polychaeta: jaws

grasping and ingesting food (bottom pic)

polychaeta: dorsal blood vessel

blood flow (1 in pic)

polychaeta: coelom

houses organs, provides hydrostatic skeleton (3)

"Oligochaeta"

earthworm, few setae, gas exchange across cuticle (skin)

earthworm reproduction

two worms align ventral sides. Sperm are released from seminal VESICLES and travel to seminal RECEPTACLES of other worm. Clitellum secretes mucus and forms a cocoon. COCOON slides forward, collecting eggs and sperm, slips off into soil, where fertilization occurs.

earthworm: seminal receptacle

store sperm from mate during reproduction

earthworm: seminal vesicles

sperm matures

earthworm: crop

store food

earthworm: gizzard

grind food

earthworm: septa

internal division of body

earthworm: heart

blood flow

earthworm: pharynx

pulls soil into buccal cavity (2)

earthworm: clitellum

Secretes mucus during reproduction

Clade Hirudinea

no setae, leeches