16 and 18
Mollusks:
- 90,000 species living species
- 70,000 fossil species
- Are coelomate lophotrochozoan protostomes; develop via spiral
mosaic cleavage and make a coelom by schizocoely. Coelom limited
to around the heart not used for locomotion
- Larval stage is trochophore
- All have a soft body
- Simple to complex; microscopic to giant.
- 80 % of molluscs are less than 10 cm in shell size.
- Herbivorous grazers, carnivores, filter feeders, detritus feeders and
parasites
- Only bivalves and gastropods live in brackish or freshwater.
- Only slugs and snails (gastropods) invaded land.
- Important food source
- Threatened by ocean acidification: calcium decline and need calcium
for shells
- Have a common basic body plan. Coelom is around the heart,
gonads and kidney. (not used in locomotion)
- Free living or parasitic
- Bilatria, unsegmented
- Triploblastic
- No asexual reproduction
Classes of Molluscs: Amphineura, Gastropoda(snails), Scaphopoda,
Bivalvia, Cephalopoda(squids, cuttlefish, octopus), Monoplacophora,
Aplacophora (sister groups: Caudofoveata and Solenogastres) and
Polyplacophora(chitons)
Form and function:
- Head-foot portion and visceral mass portion
- Head-foot:contains feeding, cephalic sensory, and locomotor organs.
Depends on muscular action
- Visceral mass: contains digestive, circulatory, respiratory and
reproductive organs. Depends on ciliary tracts
- Two folds of the skins, outgrowths of the dorsal body wall form a
protective mantle.
- Mantle: soft extension of the body wall; encloses a space between
the mantle and body wall called the mantle cavity.
- Mantle cavity houses gills(ctenidia)
- Some secrete protective shell
- Head-foot: well-developed head with mouth sensory tentacles and
photoreceptors
o Mouth: radula (a rasping, protrusible, tonguelike organ found in
all molluscs except bivalves and solengasters.
 Ribbon like with a surface full of tiny, backward-pointing
teeth
 Used for feeding
 Used to classify molluscs
o Foot: locomotion, attach to surfaces or a combination.
 Ventral, sole like structure
 Waves of muscular contraction that effect a creeping
locomotion
 Some secrete mucus
 In snails and bivalves the foot extends hydraulically by
blood.
 Some use it as parapodia
- Visceral mass
o Mantle and mantle cavity: sheath of skin extends from visceral
mass.
 protects the soft body.
 Outer surface secretes shell
 Cavity it vital:
 Products from digestive, excretory and reproductive
empty into mantle cavity
 house respiratory organs (gills or lungs)
o develop from mantle
o cilia bring in oxygen
 some aquatics have sensory receptors on mantle to
sample environmental water
 in cephalopods the muscular mantle and cavity create jet
propulsion to move
 many can withdrawl foot or head into shell
 simplest form: mollusc ctenidium (gill) is a long flattened
axis extending from wall of mantle cavity
 water is propelled by cilia over the gills
 direction of blood is the opposite
 countercurrent exchange mechanism
 incurrent chamber and excurrent chamber
o shell:
 secreted by mantle
 and lined by it
 periostracum: outer layer composed of conchiolin
 helps protect the underlayers
 secreted by a fold of the mantle edge
 growth only at the margin of the shell
 prismatic layer
 nacreour layer
o respiratory system: ctenidia, second gills or lungs and on the
body surface
o open circulatory system: pumping heart, blood vessels and
blood sinuses. Common in slow moving animals
o closed circulatory system (cephalopods)
o digestive: ciliary tract, kidneys (nephridium: opens into the
coelom by nephrostome)
 nephridium: excretory organ expels waste from body
equivalent to kidney
o reproduction
 dioecious
 trochophore larva to veliger (develops mantle, foot and
shell
 in cephalopods trochophore occurs in egg only no
free swimming
Class Caudofoveata: 120 species, wormlike, marine organisms 2 to
140 mm in lenght
- Burrowers and orient themselves vertically, with the termanl
mantle cavity and gills at the entrance of the burrow.
- Eat microorganisms and detritus.
- Oral shield(organ associated with food selection and intake as
well as a radula)
- One pair of gills
- Dioecious
- Body plan resembles ancestor molluscs.
- Sometimes called Chaetodermomorpha
Class Solenogastres: 250 species
- Marine animals similar to caudofoveates.
- No radula
- No gills
- Foot represented by a: midventral, narrow furrow, the pedal groove
- Hermaphrodite
- Bottom-dwellers
- Feed on cnidarians
- Sometimes called Neomeniomorpha
Class Polyplacophora: Chitons
- 1000 species
- Flattened dorsoventrally
- Convex dorsal surface that bears 7 or 8 articulating limy plates,
or valves
- Polyplacophora means many plate bearers
- Head and cephalic sensory organs reduced
- Have esthetes (photosensitive structures that have eyes)
- Most small
- Rocky surfaces in intertidal regions
- Stay at home organism
- Don’t go far to feed
- Scrape food with radular teeth (have iron-containing mineral
magnetite)
- Clings to rocks with its flat foot
- If detached rolls up like armadillo for protection
- Mantle girdle
- Ospharadia: chemoreceptive sense organs for sampling water occur
on the mantle groves near the anus
- Three chambered heart reaches gills y aorta and sinuses.
- Pair of kidneys (metanephridia): excretes waste to the exterior.
- Two longitudinal nerve cords connect to buccal region
- Sexes separate
- Trochophore stage without veliger stage
Class Monoplacophore:
- 25 species
- Small low rounded shell and creeping foot
- Three to six gills
- Sister taxa to polyplacophorans
Class Gastropoda: largest and most diverse
- 70,000 living species
- Snails, limpets, slugs, whelks, conchs, perwinkles, sea slugs, sea
hares and sea butterflies.
- Marine and terrestrial
- Air breathing snails and slugs.
- Sluggish, sedentary animals
- Heavy shell for protection
o One piece (univalve)
o Coiled or uncoiled
o Apex (highest point)
o Columella: central pillar in gastropods
o Right handed (dextral) or lefthanded (sinistral) depending on
coiling
o Operculum: protective plate that covers the aperature
- 1-8cm
- Marine gastropods
- Brackish and freshwater; terrestrial
- Deploy stinging cells
- Punch with foot
- Shell can secrete toxins
- Eaten by birds, beetles, mammals, fish
- Three subclasses: prosobranchia(perwinkles, limpets, whelks, conch,
abalones, cowries) opisthobranchia(sea slugs, sea hares, and
nudibranchs) and pulmonata(land and freshwater snails and slugs)
- Form and function:
o Torsion: trochophore larval stage
 Veliger larval stage
 Shell and organs Rotates 180 degrees.
 1)foot pulls shell and visceral mass 90 degrees
counterclockwise. Anus on right side
 2) rotates another 90 degrees
 Head can now be withdrawn in shell
 Called ontogenetic torsion
 Some opisthobranchs and pulmonates: undergo detorsion
o Coiling:
 All have descended from coiled, torted ancestors
 Ancestor planospiral shell
 Now: conispiral shell. Compact. Whorl over body loss of
gill, atrium and kidney on the right side in most
gastropods(prosobranchs)
o Feeding:
 Herbivourous
 Rasping particles off of hard surfaces.
 Grazers, browsers, plantonic feeders
 Some sacvengers
 Some carnivores
 Drill holes in shells
 Conus: harpoon radula, conotoxins
- Internal forms:
o Respiration:
 Ctenidum (gills)
 Pulmonates: lack gills but have lung, open to
pneumostome(opening of the mantle cavity on lung)
o One kidney (nephridium
o Nervous system: three pairs of ganglis, eyes or photorecptors,
statocysts, tactile organs and chemoreceptors
o Most have an eyecup with cornea
o Osphradium: chemoreceptive sense organ that test water
o Dioecious and monecious
 Courtship ceremonies
 Spermatozoa (sperm)
 In most fertalization is internal
- Subclasses:
o Prosobranchs: the largest, almost all marine, paraphyletic
 Gills lay in front of heart
 Incurrent from excurrent flow
 Water enter left side exits right side, drawn in cilia on gills
 One pair of tentacles
 Sexes separate
 operculum
o Opisthobrancihia: sea slugs, sea hares, nudibranchs, all
marine, monopyletic with pulmonata
 Marine shallow water
 Hid under stones and seaweed
 9 orders
 Partial or complete detorsion
 Two pairs on tentacles
 Shell reduced or absent
 All monecious
 Sea hares have earlike tentacles and vestigial shells
 Sea butterflies the foot is fins for swimming pelagic
 Nudibranchs: carnivourous, bright colored
 Sacoglossan sea slugs: radula with single tooth per row,
pierce algal “solar-powered sea slugs”
o Pulmonata: freshwater and terrestrial: lost ctenidia. Have lungs
 Some detorsion
 Monoecious
 Awautic have one pair of tentacles at the base are eyes
 Land have two pairs and posterior ones bear eyes
Class Bivalvia:
- Two shells
- Mussels, clams, scallops, oysters and shipworms
- Sedentary filter feeders depend on currents produced by cilia on gills
- No head, no radula and little cephalization
- Form and function:
o Laterally compressed
o Two shells (valves) held together dorsally by a hinge ligament
that causes valves to open ventrally; drawn together by
adductor muscles
 Umbo: one of the prominences on either side of the hinge
region
 Oldest part. Shell grows out from umbo in
concentric lines
o Pearl production: by product of protective device in animals
when something foreign is lodged between shell and mantle
- Body and mantle:
o Visceral mass: suspended from dorsal midline
o Muscular foot attached to visceral mass
o Ctenidia (gills) hang down and covered by a fold of mantle
 Dorsal excurrent
 Ventral incurrent
 Two siphons
- Locomotion:
o Extend muscular foot between valves
o Pump blood to foot causing swelling
o Acts as an anchor
o Longitudinal muscles pull animal forward
o Scallops clap their valves together to move
- Gills:
o Gas exchange both mantle and gills
o Filter feeding gills
o Water enter incurrent siphon
o Exits excurrent siphon
- Feeding
o Organic material to gills where it goes to digestive system
o Some bivavles have proboscides
o Shipworms burrow into wood and feed on particles
o Some have photosynthetic properties due to symbitosism
- Internal structure:
o Ciliary digestive tract
 Crystalline style helps digest food
 Ingested or intracellular
o Three chambered heart: two atria a ventricle
o U shaped kidneys: glandular open into pericardium, bladder
empties into suprabranchial chamber
o Nervous system: three pairs of ganglia
o Sense organs poorly developed
o Statocysts on foot, pair of pspharadia
o Scallops have blue eyes on mantle
o Reproduction: sexes separate, discharged through
suprabranchial out excurrent flow, fertilization external,
trochophore, veliger and spat
 Freshwater clams: internal
 Larval hitch hiking
- Boring: burrow in mud and sand, wood and stone
o Shipworms burrow in wood
 Fix nitrogen
Class scaphopoda:
- Tusk shells or tooth shells
- Benthic marine molluscs
- Foot used to burrow in mud and sand
- No gills gas exchange in mantle
- Detritus
- Tentacles with cilia to catch food
- Radula carries food to gizzard
- No eyes, osphradia
- Sexes separate
- Larva trochophore
Class cephalopoda
- Squids, octopus, nautiluses, devilfish, cuttlefish
- All marine
- Predators: eat fish, molluscs
- Foot merged with head
- Giant squid largest invertebrates known
- Cambrian times
- Shells: curved or coiled
- Octopuses and squids evolved from straightshelled ancestors
- Form and function:
o Nautilus have gas chambered shells for buoyancy
 Transverse septa
 Internal chambers
 Moves forward
 Siphuncle cord that runs through shell attaching body to
shell
o Cuttlefish: small curved shell enclosed by mantle
o Squids have a pen shell, thin prtein strop enclosed by mantle
- Locomotion: swim forcefully by expelling water from mantle
cavity through siphon.
o Jet propulsion
o Squid built for speed
o Cuttlefish and squid have fins
o Nautilus active at night shell keeps it upright and moves well
o Octopus: no fins globular body. Swim backwords by spurting
jetcs from siphons, can crawl
- Internal features: except for nautilus cephalopods have one pair
ogills.
o No cilia on gills
o Mantle draws in water for gills
o Waste expelled through kidneys out mantle cavity
o Radial muscles draw water in
o One way valves
o Enclosed circulatory system: reaches the gills last, branchial
heart at the base of each gill
o Nervous system: elaborate, largest brain in invertebrates.
Several lobes millions of nerve cells, giant nerve fibers
o Sense organs: eyes complex except nautilus. Cornea, lens,
chambers and retina. Orientation controlled by statocysts
 Slit shaped pupil in horizontal position
 All are colorblind except firefly squid
 Can distinguish shapes
 Octopus can learn
 Have tactile and chemorecpts on arms
 Can’t hear
o Color changing: chromatophores (contain pigment)
 Squids can send 3-4 different message simultaneously
 Color is seen as polarized
- Have ink for defense
o Acts as decoy
- Reproduction:
o Sexes separate
o Spermatozoa stores in mantle cavity
o Male arm inserts sperm into female oviduct
o Large yolky eggs undergo meroblastic cleavage
- Three subclass
o Nautiloidea : nautilus two pairs of gills
o Ammonoidea: extinct in cretaceous period
o Ceoleoidea: all other cephalopods one pair of gills
Phylogeny of molluscs:
- First arose Precambrian times
Chapter 18: Nematodes
Most important pseudocoelomate in terms of both numbers and impact on
humans.
Phylum Nematoda: Roundworms
- 25,000 species
- Other name “Nemata”
- Closer to 500,000 species
- Sea, freshwater and soil; polar regions to tropics, mountain tops to
the ocean floor.
- Parasitize every animal and many plants
o This makes it one of the most important parasitic animal groups
- Feed on bacteria, yeasts, fungai, algae; can be saprozoic or
coprozoic (live in fecal material)
- Mites, insect larvae and fungi eat nematodes
- Caenorhabditis elegans
o Free living, genome sequenced, lineage traced
- Form and function:
o Eutely; cylindrical shape; flexible, nonliving cuticle; lack of
motile cilia or flagella (except on species); and the muscles of
their body wall, running only longitudinal, not segemented
o Don’t have protonephridia
o Pharynx is muscular with triradiate lumen
o Most microscopic and less than 5cm long
o Outer body: noncellular cuticle secreted by epidermis
(hypodermis)
o Hypodermis: cellular layer lying beneath and secreting the
cuticle of annelids, arthropods and nematodes. Syncytial.
Nuclie located in four hypodermal cords
o Cuticle: shed during juvenile growth stage. Serves to
contain the high hydrostatic pressure of fluid in the
pseudocoel and used for protection.
 Made of collogen (protein of connective tissue)
o Body wall muscles lie beneath hypodermis contract only
longitudinally.
 Four quadrants.
 Muscles cells have contractile fibrillar portion (fibers) and
noncontractile sarcoplasmic portion (cell body)
 Cell body project into pseudocoel.
 Spindles striated made of actin and myosin
o Use the cuticle to help move. Muscles contract on one side and
they compress the cuticle on tht side and force contractions by
the pseudocoel. Creates thrashing motion in fluids
o Alimentary canal: mouth, pharynx, nonmuscular intestine, short
rectum and terminal anus
o Anaerobic metabolism: glycolysis
o Some are aerobic and have a kerbs cycle
o Two nerve cords (dorsal and ventral) with a ring of tissue and
ganglia located around pharynx
o Have sensory papillae on head and tail
o Amphids on head (sensory organ that leads to cuticular pit with
cilia) reduced in parasitic nematodes
o Parasitic nematodes have phasmids at posterior end (similar to
amphids)
o Dioicous
o Males smaller than female
o Fertilization internal: eggs in uterus
o Four juvenile stages separated by molt
o Ascaris lumbricoides (round worm): found in food, warm
humid regions. One billion people likely have it.
 Live in intestines
 Can be 30 cm long
 Produce 200,00 eggs a day
 Found in soil ingested by food
 Hatch once in host
 Travel through intestinal wall to heart
o Ancylostoma duodenale(hook worm): found in soil,
 11 mm long (female), 9mm (male)
 Large plates in mouth cut into intestine and suck
blood
 Can cause anemia
 Juveniles hatch in soil
 Enter the skin from soil
o Trichina spiralis
 Causes trichinosis
 Deadly
 Live anywhere in the body
 Juveniles become nurse cells (provide nutrients)
(cysts)
 Found in raw or poorly cooked meat
o Loa loa
 Eye worms
 Transmitted by fly bites
 Larvae go through blood stream
 Live in subcutaneous tissue
o Dracunculus medinensis
 Guinea worms
 Transmitted by infected copepods in drinking water
 Marvea move through body cavity
 Subcutaneous tissue where it creates ulcers exits out of
ulcer
o Dirofilaria immitis
 Heartworms
 Microfilariae
 elephantiasis
- Class Secernentea: three esophageal glands, some phasmids, both
free living and parasitic
- Class adenophorea: five or more esophageal glands, phasmids
absent, mostly free living some parasites
Phylum Nematomorpha: horsehair worms
- Have the same cuticle, epidermal cords and longitudinal muscles only
as seen in nematodes
- Sister taxa with nematodes: clade Nematoidea
- 320 species
- Free living adults, parasitic juveniles in arthropods
- Long and slender, cylindrical body
- .5 to 3mm diameter
- 1m length
- Posterior end with two or three caudal lobes
- Vestigial digestion, absorb food through body wall in host, adults live
on stored nutrients.
- No circulatory, respiratory and excretory system
- Nerve ring around pharynx
- Midvental nerve cord
- Gordian knot
- Gordius
Phylum Loricifera: 11 described species
- Tiny animals
- Protective external case (lorica)
- Live in grains of marine gravel
- Five regions: mouth cone, head, thorax and abdomen, neck
- Scalids (curved spines with sensory and locomotion function
- Cuticular plates
- Brain fills head
- Dioecious
- Dimorphic males and females
- Higgins larva
Phylum Kinorhyncha: marine worms with rotifers and gastrotrichs
- Echinodera (spiny neck)
- 179 species
- Cosmopolita
- Live mud and ssandy mud
- Head, neck, trunck region
- Trunk: 11 segments marked by spines and cuticular plates
- Introvert head and retractile proboscis.
- Scalids (spines): locomotion, chemoreception and mechanoreception
- Circular, longitudinal and diagonal muscle bands
- Cannot swim
- Hydrostatic pseudocoel
- Complete digestive system
Phylum Priapulida: 16 species of marine worms
- Colder waters in both hemispheres
- Live in mud and sand
- Tubiluchus: detritus feeder
- Cyclindrical bodies
- Introvert, trunk, and one or two caudal appendages
- Trunk: covered in spines, 30 to 100 rings
- Pharynx, straight intestine and anus
- Feed on invertebrates
Clade Panarthropoda: Phylum Onychophore and Tardigrada and
arthropoda
- Coelom reduced and hemocoel develops (major body space in
arthropods formed by fusion of embryonic coelom with
blastocoel contains hemolymph)
- A heart\
Phylum Onychophora: velvet worms
- 70 species
- Caterpillar like
- Live in rainforestsand southern hemisphere
- Predaceous: feed on caterpillars, insects, snails and worms
- Changed little in 500 million years
- Soft skin
- No segments but paired appendages
- Flexible cuticle
- Antennae with eye at the base
- Oral papillae(defensive secretion)
- 14 to 43 pairs of unjointed legs
- Crawl
- Muscular pharynx
- Straight digestive tract
- Pair of nephridia with a vesicle, ciliated funnel and duct
- Tracheal system that opens to the outside through spiracles, need
water
- Open circulatory system: pericardial sinus, dorsal heart and pair of
ostia
- Ladder nervous system
- Dioecious with paired reproductive organs
Phylum tardigrada: water bears
- Less than a mm
- 900 described species
- Most are terrestrial live on moss
- But freshwater and marine too
- Elongated, cylindrical or oval body
- Unsegmented
- Four pairs of short stubby unjointed legs with claws
- Cuticle
- Suck body fluids from nematodes, rotifers and small animals
- Mouth: buccal tube that goes into pharynx
- Hemocoel
- True coelom in gonadal cavity
- No circulatory or respiratory system
- Large brain
- Cryptobiosis
Phylogeny:
- No common cleavage pattern
- Kinorhyncha sister taxon to Priapulida: two layered pharynx
- Tardigrades are similar to rotifers but share two features with
arthropods: setae and muscles that insert on cuticle, but Tardigrades
are sister taxa with onychophorans and they are a sister taxa to
arthropods
Possess a cuticle, restrict growth
- Molted via ecdysis
- Ecdysis: Shedding of outer cuticular layer; molting, as insects or
crustaceans
o Regulated by ecdysone: molting hormone of arthropods,
stimulates growth and ecdysis, produced by prothoracic glands
in insects and Y organs in crustaceans
- Ecdysozoa phyla: composed of those taxa that molt a cuticle as they
grow
o Don’t share a common body plan
o Nematoda, Nematomorpha and Kinorhyncha are
pseudocoelomate; Priapulida might be pseudocoelomate more
research is needed.
 Used as a hydrostatic skeleton
o Loricifera can be pseudocoelomate or acoelomate
o Panarthropoda have coelomate bodies; have three phyla
 Onychophora, Tardigrada and Arthropoda
 Arthropoda is the largest phylum