Notes for Test 3

Animal Kingdom:

-Heterotrophic
-Depend directly or indirectly on plants for nutrition
-Multicellular
-Movement
-35 Phyla
-Their form is either:
a) Invertebrate – animals without backbones
b) Vertebrate – animals with backbones
-Most reproduce by sexual reproduction
a)Exception: Parthenogenesis-
-Development of an unfertilized egg into a mature individual (asexual reproduction) common in arthropods (insects).

Animalia is divided into 3 branches; we discuss the two major sub-kingdoms, Parazoa and Eumetazoa.

Parazoa (sub-kingdom 1)

Phylum Porifera:
-Sponges (pore-bearing)
-Bodies consist of many tiny pores and canals that make up the filter-feeding system
-This system accommodates their sessile lives
-Water currents flow through the canal system bringing food, oxygen and eliminating waste.
-Food is taken in by endocytosis
-Process of cellular absorption where cell membrane folds inward to take in the substance bound to its surface.
-The sponge body consists of:
-Cells which are embedded in a gelatinous matrix
-Tiny spicules of calcium carbonate or silica are also part of the matrix
-Some have a “sponge” fiber of keratose substance called spongin

These organisms have
-No definite symmetry
-No tissues or organs
-No nervous system or sense organs
-Many are colonial
-Many are brightly colored
-Larvae are free swimming but the adults are sessile
-5,000 marine species, 150 freshwater

Embryonic layers are not homologous to germ layers (no body cavity) – Porifera belong to the cellular level of organization

Form: 3 Layers
-Choanocytes: cells lining the internal cavity; they are flagellated and resemble Protists
-Mesohyl: Contains:
-Archaeocytes: (amoeboid cells) carry out various functions such as food reserves, digestion aid, carry pigments, reproductive cells, etc.
-Can differentiate to other cell types
-Example: Spicules or spongin for strength
-Epithelial Layer: Outermost layer contains flattened cells called pinacocytes

Function:
-Body openings are many tiny pores called ostia (incoming water) and a few large ones called oscula (water outlet)
-All openings are connected by a canal system
-Choanocytes maintain the water flow

Body Forms/ Canal Systems:

-Asconoid sponges: small, simple form with a tube-shaped body
-Syconoid sponges: tubular body, wall is much thicker and highly folded
-Leuconoid sponges: have most complex structure which allows for increase in body size.
-Most efficient in water circulation.

Reproduction:

-Asexual:
-External bud formation
-Some species have internal budding or gemmules
-Regeneration following fragmentation

Sexual:
-Both male and female sex cells in one individual, but not at the same time
-Sperm released into the water by one individual, then taken into canal system of another individual.

Classification:

Class Calcarea:
-Calcispongiae
-We find all body structures in this class
-Only class with spicules of calcium carbonate fringe around osculum
-Spicules are needle-shaped or 3 or 4 rayed
-All marine
-Mostly shallow waters
-Common in coral reefs of Caribbean
-Example: Sycon (Lab: Grantia)

Class Hexactinellida:
-6-rayed siliceous spicules
-Body cylindrical or funnel-shaped, 7-40 cm tall
-All marine; deep water
-Example: Euplectella (Venus' Flower Basket)

Class Demospongiae
-Leuconoid body structure
-Contains about 80% of all sponges, including the largest and most brightly colored forms
-Siliceous spicules, not 6 rayed
-One family of freshwater sponges has 150 species
-All others marine
-Includes bath sponges (lack spicules)

Class Sclerospongiae:
-Soft body covers a massive basal skeleton of calcium carbonate
-Found in coves, crevices, tunnels associated with coral reefs
-Also called Coralline sponges

Eumetazoa (Sub-kingdom #2)

Evolutionary-wise:
-The advancement of tissues, bilateral symmetry, a body cavity, deuterostome development and segmentation are the causes for differences in the Animal Phyla under the sub-kingdom Eumetazoa

Two Groups: Radial and Bilateral Symmetry

Radially Symmetrical Animals:
-Resemble a form (pie) where several cutting planes produce identical pieces
-There are not right or left sides
-There is a top and bottom (dorsal and ventral surface)
-Suitable for sessile animals (Example: sea anemone)

Body Plan:
-Show distinct tissues but no “true” organs
-Cell Layers:
-Ectoderm: Consists of epidermis, nervous system
-Mesoglea: Gelatinous substance found between the ectoderm and endoderm
-Thick in jellyfish, thin in hydra
-Contains the muscles
-Endoderm: Consists of digestive tissue or gastrodermis
-Extracellular digestion occurs in gastrovascular cavity (gut)
-Intracellular digestion in gastrodermal cells
-Improvement over sponges
-Tentacles: Most radiates have tentacles or extensible projections around the oral end
-Aid in food capture
-Nerve Cells:
-First true nerve cells (protoneurons) occur in radiates
-Arranged as a nerve net, no central nervous system
-The nerve net is never completely lost in high forms
-Sense Organs:
-Appear in radiates
-Include well-developed statocysts (organs of equilibrium)
-Ocelli: photosensitive organs
g) Locomotion:
-In the free moving forms, locomotion is achieved either by muscular contractions (Cnidarians) or ciliary comb plates (Ctenophores).

h) Unique Features:
-Nematocysts in the cnidarians (stinging)
-Colloblasts and ciliary comb plates in the ctenophores (adhesive).

Two Phyla of Radially Symmetrical Animals:

*Phylum Cnidaria:
-Also called coelenterate (sac-like body cavity).

1. Jellyfish, hydroids, sea anemones, and corals.
2. 10,000 species – named from cnidocysts which contain the stinging structures (nematocysts).
3. Widespread in marine habitats, some found at great depths.
4. Few fresh water forms; no terrestrial species.
5. Sessile or slow moving.
6. Efficient predators of organisms that are more complex and swift.
7. Algae may live as mutuals in their tissue; notably in some fresh water hydras, jellyfish, and in reef building corals.

Cnidaria Have Two Different Body Forms:

1. Polyp
-Cylindrical- found attached to a firm substrate
-Mouth parts facing upwards
-Live a solitary lifestyle or colonial

2. Medusa
-Umbrella or bowl-shaped
-Usually free floating
-Mouth points downward (polymorphism)
-Tentacles hang down
-Many have sensory organs on the margin of the bell or umbrella.
-Pigment spot: sensitive to light
-Statocysts: organs of equilibrium
Cnidarian are usually a polyp or medusa or an alternation between the two forms.

Reproduction:

1. Asexual: Polyps bud becoming a polyp or medusa
2. Sexual: Fertilized eggs give rise to planulae (free swimming, multicellular, ciliated larvae) external fertilization.

Starting Now We Have:

-Digestion of food within a gut cavity
-Fragments of food are absorbed by cells along the cavity
-One opening (mouth and anus)

No Respiratory or Excretory Systems

1. No special organs because tissue is so thin.
2. Excretion taken care of by diffusion of nitrogenous wastes (ammonia)

Cnidocytes- cells on end of tentacles and sometimes on the body which contain nematocysts.
-Nematocyst: found within the cnidocytes and are a harpoon-like structure.
Three types of nematocysts:
1. Penetant: harpoon-like structures used to penetrate
2. Glutinant: sticky surfaces used to stick to prey
3. Volvent: lasso-like string fired at prey; wraps itself around cellular projection on the prey.

Classification:

1) Class Hydrozoa (Hydroids)
-Most have polyps and medusa stages
-Most are marine organisms; some bioluminescent.
-Colonial hydroids are found in shallow coastal water attached to mollusk shells, rocks, wharves, and other animals.
-Some are found at great depths.
-Example: Portuguese Man-of-War (Physalia)
-Marine; floating colony; have gas-filled, balloon-like floats
-Example: Hydra (freshwater, no medusa stage)
-Tolerates considerable eutrophication, wide temperature fluctuations, and saline conditions.
-Widespread, though sensitive to heavy metal toxicity.
-Example: Obelia: Marine, colonial hydroid.

2) Class Scyphozoa
-Jellyfish; all marine
1. Dominant stage is medusa (bell shaped)
2. Gelatinous mesoglea much enlarged
3. Example: Aurelia (tentacles are short)

3) Class Cubozoa
-Box Jellyfish
1. Box shaped, tentacles trail from the “corners” of the translucent body
2. Fastest swimmer among jellies
3. The most deadly cnidocytes are found on the box jellyfish's body.
4. Sea Wasp, Chironex fleckeri is claimed to be the most venomous marine animal known.
5. Certain species prevalent along the Florida and Texas coasts.

4) Class Anthozoa
-Sea anemone, hard and soft corals, sea fans, sea pens, etc.
1) Flower animals (Greek, antho = flower)
2) Polyps (no medusa stage)
3) Solitary and colonial
4) Sea anemones have simple, tubular tentacles
5) Lowest sting intensity
6) Sea anemones and hard corals have a hexamerous plan (in six or multiples of six)
7) Hard corals have a hard skeleton of calcium carbonate with many minute depressions that have been formed by the polyps.
8) Sea fans, sea pens and soft corals are octamerous
-Have eight pinnate tentacles arranged around the margin of the oral disc.

3) Phylum Ctenophora
-Comb jellies, sea walnuts, etc.
1. Structurally complex than cnidarians.
2. Transparent and bioluminecent.
3. Spherical or ribbon-like shape
4. Locomotion: Eight comb-like plates of fused ciliar are arranged along sides of animal (largest animal to use ciliar)
5. All are free swimmers
6. Have anal pores (not just one pore like the jellyfish
7. Do not have nematocysts; are harmless to humans
-Capture prey with sticky cells called colloblasts.


Bilateral Symmetry:

Terms:
Dorsal- Top
Ventral- Bottom
Anterior- Toward the head/top.
Posterior- Toward the back/ tail/ feet.

The Three Types of Body Cavities That Evolved With Bilateral Symmetry:

1. Acoelomates: which have no body cavity other than a digestive system.
-Example: Planaria (flatworm)
2. Pseudocoelomates: body cavity located between the mesoderm and endoderm.
-Example: Nematodes (round worm)
3. Coelomates: body cavity is fluid-filled and develops within the mesoderm.
-Example: Mollusks, Insects, Chordates. Have a true coelom.

[Know page 56 Fig 3.2 and page 58 Figs 3.5 and 3.7]

Development Styles:

Protostomes and Deuterostomes: both terms refer to the development of the embryo and pattens of growth surrounding the fate of the blastopore (Page 61, Fig 3.8)

1. In protostomes, the blastopore becomes the animal's mouth (develops first)
2. In deuterostomes, the blastopore becomes the animal's anus (develops first), the mouth develops elsewhere.

Body Styles:

Non-segmented to segmented denotes advancement in the body plan by subdividing the body.

Acoelomate Animals:

Phylum Platyhelminthes (flatworms)

1. Flatworms (Lab: Dugesia, common name planaria)
2. Most are parasitic (tapeworm), some are free-living (planaria)
3. Economically important (tapeworm, etc.)
4. Cilia for moving
5. Simplest animals in which organs occur
6. Most have only one opening to the digestive cavity (cannot feed, digest, and eliminate at the same time).

Phylum Platyhelminthes' Systems:

A. Excretory System:

-Network of 5 tubules with flame cells on the side branches. Main function is to help with water balance (osmoregulation).
1. Flame cell cilia push wastes out exit pores which are located between the epidermal cells.
-Waste removal is a secondary function
2. Most wastes diffuse into the gut and exit through the mouth.

B. Circulatory System:

-Do not have; they have simple diffusion for oxygen and food.

C. Nervous System:

-Some have a nerve net like cnidarians
-Most have a simple central nervous system with longitudinal nerve cords with tiny swellings at the anterior ends of the nerve cord (primitive brain)
-Eyespots are at anterior end
-Inverted pigment cups that are light sensitive (connected with nervous system)

D. Reproductive System (most)

-Most are hermaphroditic (both male and female sex structures in one).
-Many have internal fertilization.
-Asexual (regenerative reproduction) possible.

Three Classes of Flatworms:

A. Class Turbellaria

1. Free-living, soft flattened bodies
2. Ciliated epidermis
3. Locomotion: gliding over a slime tract secreted by marginal adhesive glands on epidermis.
4. Mouth located ventrally – near center of body
5. Example: Dugesia (planaria) is fresh water
-Size: very small, some less than 5mm long, some even smaller than large Protozoans
-Largest species over two feet long.

B. Class Termatoda (flukes)

1. Adults are endoparasitic of vertebrates
2. Lack cilia, eyespots, sensory organs of free-living flatworms (don't need them once they are in the host).
3. Life cycle is indirect- at least one intermediate host that is always a mollusk-type
4. Attach to body of host via suckers, anchors, or hooks.
-Have powerful oral suckers around the mouth
-Most also have a mid-ventral sucker called the acetabulum
-Example: Clonorchis sinensis: Human (Chinese) liver fluke
-Life Cycle: First host snail; second host fish where cercariae burrows under scale; third host human when he/she eats raw fish.
-Treatable but difficult
-Hermaphroditic except scistosomes
-Scistosoma (lab): Dioecious (separate male and female)
-First intermediate host is snail
-Parasite can live up to 48 hours in water
-Parasite enter human through skin
-Tropical and temperate countries, not U.S.
-200 million are affected, 1 million die per year, can be cured
-Spread by urinating or defecating into water used by others.

C. Class Cestoda (Tapeworm):
1. Endoparasitic (in vertebrates)
2. Nonciliated
3. Lack digestive organs- obtains food through the body wall
4. Example: Taenia Saginata (lab)- beef tapeworm
a) Attaches to any part of the intestinal wall in humans with suckers and/or hooks
b) Can be picked up by eating beef that is cooked rare.
c) Can grow to 36 feet in length
-Scolex located at anterior end- includes attachment organs
-Segments are called proglottids and can break off
-Embryos in proglottids can then be ingested by cattle/humans
-Need to remove entire worm, not just segments to kill worm.

Phylum Nemertea:
1. Ribbon or proboscis worm (rare), evolutionarily important.
2. Mostly marine animals
3. Proboscis used for capturing prey
4. Simplest animal with a complete digestive system (like Phylum Nematoda)
-2 separate openings, a mouth and an anus (more advanced than Platyhelminthes,but less successful as a group)
-Many important evolutionary trends start with Phylum Nemertea; eg first circulatory system with blood vessels

(last acoelomate)

Psuedocoelomates:
-The pseudocoelomate phyla have a pseudocoel (a false cavity) rather than a true coelom
-This is the second basic body plan
1. Pseudocoelom acts as a hydrostatic skeleton
-Becomes rigid when filled with fluid
-Allows muscle contraction and therefore more efficient movement.
2. No defined circulatory system
3. Has a complete digestive tract
4. The epidermis in many secretes a non-living cuticle with some specializations like bristle, spines, etc.
5. There is a constant number of cells or nuclei in the individuals of a species, this condition is known as eutely
-Some nematode species, identification is based on eutely

Phylum Nematoda (Roundworms):
1. Found in all different ecological niches- salt and freshwater, on land, from the ice caps to tropical areas.
2. Free living or parasitic
-Found everywhere; plants and animals
-Economically very important

Characteristics of Phylum Nematoda:
1. Body is cylindrical in shape and unsegmented
2. Body covered with flexible, thick, non-living cuticle that molts as they grow.
3. Muscles in body wall run in longitudinal direction only.
a) No circular muscles in body wall (4 bands, 4 epidermal cords)
4. Mouth usually has 16 raised, hairlike sensory organs
-Stylets: piercing organs (near mouth)
5. No flagella or cilia
6. Excretory System: consist of cells that function as glands or canals (no flame cells)
a) The alimentary canal consist of a mouth → muscular pharynx → long muscular intestine → short rectum → terminal anus.
7. Reproduction: Sexual
a) Males reproductive system opens into rectum to form cloaca
b) Females reproductive system opens into separate gonospore
-Example: Necator- Hookworm
a) Humans, pets, etc.
b) Anterior end curved into a hook-like structure
c) Have cutting plates in mouth; cut into intestinal mucosa
d) Sucks blood of host
e) Suck more than they need, may cause severe internal bleeding and anemia
-Ascari- Intestinal roundworm (we dissected this)
-Most common parasite in humans
-Large numbers of worms can cause intestinal blockage
-28% of humans in 3rd world countries
-Enterobius- Pinworms
-Single host can reinfect self or others
-The larvae hatches in the intestine and cycle starts over
-In U.S. 16% adults and 30% children infected
-Trichinella- Disease trichinosis
-Adult worms burrow into mucosa of small intestine
-Female produces living young (this is very important!)
-Juveniles penetrate into blood vessels; carried through the body
-Penetrate skeletal muscle forming a cyst
-Humans usually get this parasite from eating poorly cooked pork

(ALL OF THE ABOVE ARE INTESTINAL PARASITES)

(still in the Phylum Nematoda)
-Filarial Worms:
a) 8 species which infect humans
b) Major causes of several disease in humans
c) 250 million people in tropical climates are infected
d) Wuchereria bancrofti – Lives in the lymphatic system
-Disease symptoms: inflammation/obstruction of the lymphatic system
-Disease is called Elephantiasis (long/repeated exposure)
-Condition marked by excessive connective tissue growth and enormous swelling of affected parts (vector: mosquito)
e) Another filarial worm causes river blindness which is carried by black flies
-Affects 30 million people mostly in tropical areas (Africa, Arabia, Central/South America)

Phylum Rotifera:
1. Rotifers look like a trumpet
2. Name derived from the ciliated crown or corona, which when beating looks like a rotating wheel.
3. Variety of sizes, shapes, and colors.
a) Floaters (globular shaped and sac-like)
b) Creepers and swimmers (elongated, worm-like)
c) Sessile, vase-like
d) Some are colonial
4. Most species are freshwater forms; a few are marine, terrestrial, or parasitic
a) Generally found on the bottom region (benthic zone) of water way.
5. Body is made up of a head, trunk and foot
a) Head bears the corona which surrounds the mouth
b) Trunk contains primitive organs
c) Trunk sometimes ends in a “foot”
d) Toes secrete a sticky material used in attachment
6. Rotifers are dioecious
a) Male unknown in many species and reproduction is entirely parthenogenic.

Phylum Cycliophora (discovered in 1995)
1. Very tiny, as big as a full-stop
2. Live on the mouth-parts of Norwegian lobster (bristles) and other crustaceans, follow lobster's life cycle (molting)
3. Individuals are only a brain and sex organs

Coelomates:

These individuals have:
-Protostomes: Mollusks, annelids, arthropods
-Deuterostomes: Echinoderms, hemichordates, chordates

Phylum Annelida: (Earthworms, marine and freshwater worms, leeches)
-Worldwide distribution: marine, brackish, freshwaters and terrestrials

1. Segmentation or metamerism (also arthropods)
a) Metamerism means the animal is composed of “serially repeated units called segments or metameres”
b) First segmented animals
c) Segmented internally and externally.

A. Body Plan- General:
1. Tube within a tube with the digestive tract suspended within the coelom
-Digestive system is complete and not metamerically arranged.
2. Coelom (body cavity) is divided by septa.
-Septa: are partitions that divide the segments internally, except in leeches.
-Septa = more powerful for burrowing
-Coelomic fluid supplies pressure an functions as a hydrostatic skeleton.
3. Externally, body divided into similar rings or segments arranged in a linear series, marked by circular grooves called annuli.
-Setae: Tiny, chitinous bristles found on each segment.
-Short ones- used during movement to anchor and prevent backward slipping
-Long ones- aid aquatic annelids in swimming
-Often present on fleshy appendages called parapodia
-Absent in leeches
4. Muscles are used to crawl, burrow, swim

B. Nervous System is Centralized
1. Cerebral Ganglion in an anterior segment (brain)
-Separate ganglia (or nerve centers) in each segment
-These are interconnected by nerve cords
-Have sense organs such as taste buds, photoreceptor cells, some have eyes with lenses

C. Respiration:
-Oxygen and CO₂ diffuse through body surface.

D. Circulatory System
1. Closed with muscular blood vessels and aortic arches (heats) move blood.
-More complex than previous organisms

E. Excretory System:
1. Nepheridia: (kidney) found in each metamere
2. Have reached differentiation that involves removal of waste from blood as well as from coelom -Collects wastes and transports it out of the body through the coelom by way of excretory tubes.

F. Reproduction:
1. Hermaphroditic or separate sexes
2. May have larva, if present are trochophore type (structure)
-Small, free-swimming, ciliated larvae (1st stage)
3. Some have asexual reproduction via budding

G. Annelids are the most highly organized animals capable of complete regeneration
-Ability greatly varies within a group

Classes: they are classified on the basis of the presence or absence of parapodia, setae, and metameres

Class Polychaeta:
-Commonly known as bristleworms
1. Most primitive of the annelids; largest class, mostly marine
-Size range from less than 1mm to 3 meters in length
2. Extremely important component of marine food webs
3. Most abundant organism in soft marine sediment
4. Many are commensal
-Live in or with other animals; i.e. sponges, shells of mollusks, echinoderms, crustaceans
5. Others are parasites or predators
6. Parapodia:
-Use setae on edges of parapodia to anchor/hook to bottom
-Paired, fleshy paddle-like flaps
-Found on most segments
-Used for locomotion (burrowing, swimming, crawling, etc.) and gas exchange (surface area)
7. Separate sexes
-External fertilization usually
8. Have a trochophore larvae like the mollusks.
-Lab: Nereis (the one whose pharynx we tried to pull out) and Arenicola (lugworm)

Class Oligochaeta (Earthworms)
1. Most are terrestrial; some freshwater (What happens when it rains? Burrows flood and they all come to the surface)
2. Many segments- tropical forms have up to 250 segments
-Mouth on first segment; anus on the last
3. Suck in organic and other material by a contracting pharynx
4. Digestive tract- (gizzard) part of
-grinds up organic material
-Leave casting (earthworm poop), rich soil, aerate soil
5. No eyes
-Have light and touch sensitive organs
6. No parapodia and fewer setae than polychaetes
7. No distinct head region
8. Hermaphroditic with cross-fertilization
-Nose to toes ventrally for sperm exchange
-Stick together via mucus from clitellum (thick band on earthworm's body)
-After mating, clitellum produces a sac which goes down worm
-Called a cocoon; located on the outside of the worm. Picks up sperm and egg along the way.
-Eggs are fertilized in the cocoon
-The cocoon is dropped off in the soil
-Lab: Lumbricus (earthworm)

Class Hirudinea (leeches)
1. Flattened dorso-ventrally, like flatworms
2. Hermaphroditic
-Have clitellum only during breeding season
3. Have a reduced coelom and continuous throughout the body
-No individual segments like the other 2 classes
4. Have suckers at one or both ends
-Sometimes used for locomotion
5. No parapodia or setae
6. Most are predators or scavengers and some are external parasites
7. Example: Blood-sucking leech: Hirudo medicinalis
-Have mouth with chitinous jaws and they secrete an anticoagulant called hirudin.

Phylum Mollusca
-Chitons, snails, slugs, nudibranches, clams, mussels, scallops, oysters, squid, octopi, nautiluses, etc.
1. Size: The group ranges from microscopic (bivalve seed shells), to a giant squid and giant clam.
2. New characteristics: fleshy mantle which, in most cases, secretes a shell, the radula, and a muscular foot.
3. Movements: hardly moving (bivalves; sessile) to very fast (squid)
4. Mode of feeding: includes grazers, predators, and suspension feeders
5. Locations: great range of habitats from the tropics to the polar seas; from shorelines to ocean depths
-Originated in the sea
-Bivalves and gastropods in brackish and freshwater habitats
-Only snails and slugs (gastropods) invaded land
-Require humidity, shelter and calcium in the soil to make shell

They Phylum Mollusca is an important food source to many other species as well as for decorative objects such as pearl buttons and jewelry.

A. General Body Plan
1. Head at anterior end of body
2. Highly developed direct eye of higher mollusks (from skin) is compared to the indirect eye of the vertebrates (brain eyes)
3. Visceral mass- where the digestive, excretory, and reproductive organs are found.
4. Foot- Muscular- used for locomotion, attachemtn, or capturing of food
5. Dorsal body wall forms two folds called the mantle, inside of which isth e mantel cavity.
-Mantle cavity- holds gills and lungs = respiration
-Also secretes the sell-shell absent in some
-Protective shell has 3 layers:
a) Outer- horny layer rich in protein
b) Middle- calcium carbonate crystals
c) Inner- pearly layer
-Found in clams and oysters = pearls (from nacre)
6. Radula: rasping, tongue-like organ used to scrape food off of substrate (not bivalves- they are suspension feeders)

B. Respiration; Gas Exchange:
-Occurs not only through the body surface as in lower invertebrates, but also by specialized respiratory organs in the form of gills or lungs


C. Circulatory System:
1. Open circulatory system
-Coelom is a small area surrounding the heart
2. In most cephalopods the circulatory system is closed (octopus, squid) more efficient than previous organisms.
-Closed circulatory system allows for larger size: cephalopods the largest invertebrates

D. Excretory System
1. Consists of 1 or 2 tubular structures called Metanephridia: removes wastes

E. Reproductive System:
1. Most are dioecious, some hermaphroditic
2. Trochophores: Free-swimming larvae, first stage
-Propelled by cilia which are found around the center of the body
3. Veligers: second free-swimming stage after trochophores.

Classes of Mollusks:
-7 Classes, we will look at 4

A. Class Polyplacophora: Chitons
1. Primitive marine mollusks found on rocks and seaweed in the intertidal zone
2. All have 8 shell plates, generally oval in outline and a flattened body
3. The shell plates consist of articulation calcareous valves (roly poly)
4. Creeping foot; a primitive feature in mollusks
5. Trochophore larva is present, no veliger larva
(The annelid has ancestral characteristics)

B. Class Gastropoda: (Belly Foot: Snails, conchs, slugs, etc.)
1. Largest, most diverse group of mollusks
-Make up 70% of all mollusks; are found in marine, freshwater and terrestrial habitats
2. Visceral mass (body) is asymmetrical with spiral shell serving as a retreat rather than a shield.
3. Muscular foot used for “creeping” locomotion, modified for swimming or burrowing
4. Operculum: a horny plate that seals the opening
5. Tentacles and eyes on head (1 or 2). Longer ones have eyes on end
6. Radula: tongue-like organ
7. Feeding habits: graze, browse, and feed on plankton, scavengers, detritivores, and carnivores
8. Important in food chains and serve as pollution/ acid rain indicators.
9. Intermediate hosts for many important parasites.

C. Class Bivalvia: Clams, scallops, mussels, oysters
1. Mostly marine, freshwater also
2. Two shells, hinged together dorsally
3. Large, muscular wedge-shaped foot for creeping, burrowing, cleaning
4. Adductor muscles-draws shells together
5. Incurrent and excurrent siphons for filtering water
6. No distinct head
7. No radula (radula is a primitive feature)
8. Most are sessile suspension feeders
9. Important economically for food and for saltwater pearls.

D. Class Cephalopoda (means head-foot: octopus, squid, nautilus)
1. Marine predators- swift swimmers
2. Characterized by a completely emerged head and foot
-Foot has evolved into a series of tentacles
-Adhesive structures, suction cups, hooks
-Squid = 10 tentacles; Octopi = 8 tentacles; Nautilus = 60-80 tentacles
3. Horny, beak-like pair of jaws
4. Radula present
5. Nervous system- highly developed with great nerve fibers and a brain
6. Eyes- are very elaborate and retina is similar to vertebrates
7. Most intelligent invertebrates
8. Closed circulatory system
9. No external shell except for few species of the nautilus
-Squid, cuttlefish = pen, cuttle-bone
10. Some have a dark fluid (melanin) in special sacs used for protection.
11. Movement- have directional jet propulsion
-By means of water movement through their modified mantel cavity
12. Reproduction
-Dioecious
-Sperm stored in spermatophores
-No larval stage; development is direct
13. Color changes
-All except nautilus can change color and patterns due to chromatophore cells.
-Response to danger or emotion (hormonal control)
14. Economic Importance
-Food, shells for decoration, cuttlefish bone calcium source for pet birds.