Invertebrates
Chapter 27: Simple Invertebrates
Section 1: Sponges (Phylum Porifera)
I. Body Plan – built for filter-feeding; lacks true
tissues
A. Ostia – tiny pores through which water
enters & travels to an internal chamber
B. Choanocytes (collar cells)
1. Line internal chamber.
2. A flagellum moves water through sponge &
out a large opening called an osculum.
3. Trap nutrients from the water & transfers
them to mobile amoebocytes, which in turn
transports nutrients & wastes.
C. Skeletons
1. Spicules – needle of silica or calcium carbonate
2. Spongin – protein fiber in some sponges
II. Reproduction – sponges are hermaphrodites
A. Sexual
1. Gametes are produced at different times
2. Sperm are released from sponge, eggs stay
3. Sperm enter another sponge as water is
drawn in
4. After fertilization, larvae leave, attach to a
surface, & develop into an adult
B. Asexual
1. Shed fragments that then produce new sponges
2. Cluster of amoebocytes with food supply can
grow into an new sponge
3. Regeneration – a piece or cell of a sponge can
grow into a new sponge
Calcerous Sponge
Demosponge
Glass Sponge
Section 2 – Phylum Cnidaria
I. Characteristics
A. General
1. 2 layers of tissue – outer epidermis, inner
gastrodermis
2. Radial symmetry
3. 2 body forms
• Medusa – free floating, mouth pointed down
• Polyp – sessile (anchored), mouth pointed
up, tube-like
B. Movement & Response
1. 2 nerve nets, one per tissue, to coordinate
movements
2. Sensory cells detect light, chemicals, and
mechanical stimuli
C. Feeding
1. Tentacles are armed with cells called cnidocytes
• In each is a nematcyst, a threadlike
organelle that contains toxins for defense &
capturing prey.
2. When triggered, nematocyst shoots out, lodges
inside prey, inject poison (paralysis), &
tentacles bring prey to mouth
D. Reproduction
1. Most alternate between a polyp & a medusa
stage
E. Groups of Cnidarians
1. Hydrozoans – both polyp &
medusa stages in life cycle;
Ex: Hydra, Portugese man-of-war
2. Scyphozoans – mostly as
medusas; Ex: jellyfish
3. Anthozoans – mostly as
polyps; Ex: anemones & corals
II. Phylum Ctenophora
A. Move by beating rows of cilia
B. Tentacles hold colloblasts, cells that
contain a sticky substance to bind prey
C. Exhibit bioluminescence – can produce
light
Section 3: Flatworms
(Phylum Platyhelminthes)
I. Characteristics
A. General
1. Acoelomates – lack a body cavity, or coelum
2. Bilateral, 3 germ layers (ectoderm, mesoderm,
endoderm), cephalized
3. Very flat!
B. Body Plan
1. Tissues are organized into organs & muscles.
2. Gastrovascular cavity has 1 opening
C. Movement & Response
1. Primitive brain & nerve system coordinate
muscle movement
D. Feeding
1. Most are carnivores with a branched
gastrovascular cavity that runs throughout
worm’s tissues.
2. Tapeworms are parasitic, lack a gastrovascular
cavity, so absorb nutrients across their skin.
E. Respiration & Circulation
1. Each cell lies close enough to the outside
environment that gases simply diffuse in/out.
F. Reproduction
1. Most are hermaphrodites & reproduce sexually.
2. Some (planarians) reproduce by fragmentation.
II. Groups of Flatworms
A. Turbellaria
1. Most are marine
2. Move with cilia (small worms) or wave-like
muscle contractions (larger worms)
B. Cestoidea – tapeworms
1. Parasites
2. Head is called a scolex & has suckers/hooks for
grasping tissue of host.
3. Body is many segments (proglottids),e ach
containing both male & female sex organs.
4. Mature proglottids, holding up to 1000
fertilized eggs, contaminate meat and are
ingested.
Tapeworm Life Cycle
C. Monogeans & Trematodes
1. External (monogeans) & internal (trematodes)
parasites of animals
2. Life Cycle:
Section 4 – Roundworms
(Phylum Nematode)
I. Characteristics
A. 3 germ layers, bilateral symmetry
B. Pseudocoelom – body cavity that forms
between mesoderm & endoderm; not a
true cavity!!!
C. Has simple muscle & nerves for movement
D. Fluid moves in & through pseudocoelom
to transport nutrients & wastes
E. Sexual reproduction – separate sexes
II. Groups of Roundworms
A. Pinworms – intestinal parasites of humans
B. Hookworms – intestinal parasites of humans
C. Filarial worms – line blood/lymphatic tissues
Ex: Elephantiasis (condition); dog heartworms
D. Ascarids – intestinal parasites of pigs,
horses, & humans
Chapter 28 – Mollusks & Annelids
Section 1: Phylum Mollusca
I. Characteristics
A. Basics
1.
2.
3.
4.
Soft-bodied coelomates – have true body cavity
Bilateral symmetry
Most secrete a shell of calcium carbonate
3-part body plan
B. Body Plan: 3 Parts
1. Visceral Mass – main, soft body that contains
organs
2. Mantle – tissue fold over visceral mass that
secretes the shell
3. Foot – muscular foot is for locomotion
II. Organ Systems
A. Digestive System
1. Can be filter feeders (clams), herbivores (snails),
or carnivores (octopus)
2. All have a radula – made of 1000’s of pointed,
backward-curving teeth in rows
B. Excretion
1. Coelum is collecting place for waste
2. Cilia pulls fluid from coelum into tubular
structures call nephridia, which recovers
nutrients
C. Circulation
1. Open circulatory system with a 3-chambered
heart
2. Exception: octopus has a closed circulatory
system
D. Respiration
1. Most exchange gases via gills
2. Snail exchange gases through their skin
E. Reproduction
1. Most are separate sexes, but some snails/slugs
are hermaphrodites.
2. Indirect development – fertilized eggs develop
into a type of larval called a trocophore.
3. In octopus & squid, larval stage occurs inside
fertilized eggs & a juvenile mollusk hatches.
III. 3 Classes of Mollusks
A. Gastropods – snails, slugs
1. Foot is for locomotion on land or swimming
2. Most are herbivores, but some use their
radula to bore holes or inject poison into prey.
B. Cephalopods – squid & cuttlefish (internal
shells), octopus (no shell), & nautilus (shell)
1. Large head (cephal) attached to tentacles (pod)
2. Squid – 10 tentacles; octopus – 8 tentacles;
nautilus – 80-90 tentacles!
3. Complex brain & nervous system = most
intelligent of invertebrates
4. Siphon – hollow tube drawing in and expelling
water (or ink!!)
C. Bivalves – clams, mussels, oysters, scallops
1. 2 part, hinged shell
2. Most are filter-feeders
3. If a piece of sand gets lodged between mantle
& shell, it is coated with nacre which, after
many layers, becomes a pearl.
Section 28-2: Phylum Annelida
I. Characteristics
A. Basics
1.
2.
3.
4.
Coelomates
Bilaterally symmetrical
Coelum contains complex, specialized organs
Segmented – coelum is divided by septa,
creating many segments
5. Most have external bristles called setea
II. Body Systems
A. Closed Circulatory System
B. Nephridia for excretion
C. Digestive gut with separate mouth & anus
D. Respirates across skin; no gills or lungs
E. Nervous System
1. Primitive brain = cerebral ganglia
2. Nerve cord runs from brain along underside of
worm’s body
Annelid Anatomy
F. Reproduction & Development
1. Sexual reproduction with a trocophore larval
stage (incomplete development)
2. Annelids add new segments to tail throughout
lifetime
III. Annelid Classes – based on # of setea & presence
of parapodia (flap-like appendages)
A. Class Polychaeta (many setea)
1. Marine segmented worms
2. Pair of parapodia per segment with setea
extending from each parapodia
3. Parapodia are used for locomotion and/or gas
exchanged
4. Either burrow into ocean floor or live in tubes
5. Filter-feeders or predators
Class Polychaeta
B. Class Oligochaeta (few setea)
1. Earthworms & freshwater segmented worms
2. No parapodia and only a few setea per
segment
3. Reduced head: no eyes, but light- and touchsensitive structures at both ends of the body
4. Scavengers: ingest soil
• Unabsorbed nutrients pass through anus in
a form called castings
• Castings are useful for soil fertilizer
Class Oligochaeta
C. Class Hirudinea (no setea)
1.
2.
3.
4.
Leaches
No parapodia or setea
Not internally segmented
Predators or scavengers
• After cutting or digesting a hole into host’s
skin, an anticoagulant (prevents clotting) is
released into host’s blood
• Can ingest 10 times its own weight in blood
Class Hirudinea
Chapter 29: Arthropods & Echinoderms
Section 29-1: Arthropods
I. Characteristics
A. Basics
1.
2.
3.
4.
5.
Segmented, Coelomates
Bilateral
Jointed appendages (arthropod = joint footed)
Hard exoskeleton made of chitin
Open circulatory system with a heart
B. Segmented Bodies = 3 parts
1. Head – cephalized!
2. Thorax – mid-section where legs & wings are
usually found
3. Abdomen – last, tail end of body
4. Cephalothorax – in some arthropods, the head
& thorax are fused (crabs)
C. Exoskeleton – made of 3 layers
1. Outer, waxy layer repels water
2. Middle layer is made of chitin for protection
3. Inner layer is also made of chitin, but is more
flexible, mainly at joints
4. Does not grow with arthropod, so must be
shed
II. Body Systems
A. Respiration
1. Most land arthropods – air enters body
through spiracles, openings that lead to tubes
called trachea.
2. Other land arthropods breathe with lungs.
3. Aquatic arthropods use gills.
B. Feeding & Digestion
1. Each group has different mouth parts for
feeding.
C. Excretion
1. Malpighian tubules – extension of lower
intestinal tract, bathed in blood
2. Blood is filtered here, but all wastes remain in
the gut and leave through the anus.
D. Other features
1. Compound Eyes – made of 1000’s of individual
focusing lenses.
2. Molting – shedding of exoskeleton; leaves
arthropod vulnerable until a new one is
grown.
III. Groups of Arthropods (Subphyla)
A. Trilobita – extinct trilobites
B. Chelicerata
1.
2.
3.
4.
Chelicera – modified pincers or fangs
4 pairs of walking legs
No antennae
Ex: spiders, scorpions, mites, ticks, horseshoe
crabs
C. Crustacea
1.
2.
3.
4.
Chewing mouth parts (mandibles)
2 pairs of antennae
Breathe with gills
Ex: shrimp, lobster, crabs, crayfish, barnacles
D. Myriapoda
1. Mandibles & antennae
2. 1 or 2 pairs of legs per segment
3. Ex: centipedes & millipedes
E. Hexapoda (Insects!!)
1. Body divided into all 3 parts
2. Antennae & mandibles
3. 3 pairs of legs & 2 pairs of wings
Section 29-4: Echinodermata
I. Characteristics
A. Basics
1. Echinoderm = spiny skin; known for spines or
bumps that project through the skin
2. Internal skeleton
3. Radial symmetry (not cephalized) in adults
4. Water-vascular system
5. Breathe through the skin
Echinoderm Diversity
B. Endoskeleton
1. Made of ossicles, small calcium carbonate
plates
2. In many echinoderms, ossicles bear spines
which characterize this phylum
C. Symmetry
1. Indirect development: larva have bilateral
sysmmetry
2. Adults develop a 5-part radially symmetric
body with arms radiating from a central point
3. No cephalization: central nerve ring with
branches of nerves travelling to each arm
D. Water-Vascular System
1. Water enters through a pore called the
madreporite.
2. Water then travels through a central ring &
into interconnected canals that lead to the
arms.
3. Attached to these canals are tube feet,
through which water leaves.
• The ampulla is a bulb-like part of tube feet
that contracts & forces water out
• Used to move, grip, & manipulate objects
Water-Vascular System
II. Echinoderm Diversity
1. Sea stars = starfish
2. Brittle Stars – arms are more narrow & even
branched
3. Sea lilies & feather stars – cannot move
4. Sea Urchins & Sand dollars – lack arms but have spines
5. Sea cucumbers – slug-like
appearance but have 5-part,
radial water-vascular system
with tube feet