Chapter 33A:
An Introduction to Invertebrates I
1. Porifera
2. Cnidaria
ANCESTRAL PROTIST
Common ancestor of all animals
Porifera
Cnidaria
Lophotrochozoa
Ecdysozoa
Deuterostomia
Bilate
ria
Eum
etazo
a
Invertebrates Animals without a backbone (vertebral column) are called invertebrates.
• over 95% of known animal species are invertebrates
1. Porifera
Porifera
Cnidaria
Lophotrochozoa
Ecdysozoa
Deuterostomia
General Characteristics of Porifera
All animals in the phylum Porifera are informally referred to as sponges which have the following characteristics:
• sessile (non-motile, sedentary) filter-feeders
• lack body symmetry
• do not have any defined tissues
• most are hermaphrodites (produce both eggs and sperm)
The characteristics in RED are unique in the Animal Kingdom.
The Structure of a Sponge
Spongocoel
Pores
Epidermis
Water flow
Mesohyl
Amoebocytes
Spicules
Flagellum
Osculum
Choanocytes Collar
Food particles in mucus Choanocyte
Phagocytosis of food particles
Amoebocyte
Azure vase sponge (Callyspongia plicifera)
• choanocytes (or collar cells) draw water into the spongocoel through pores
• choanocytes capture food to transfer to amoebocytes that distribute food to other cells
2. Cnidaria
Porifera
Cnidaria
Lophotrochozoa
Ecdysozoa
Deuterostomia
Eum
etazo
a
General Characteristics of Cnidarians
All animals besides the sponges belong to the clade Eumetazoa, animals with true tissues. One of the oldest groups of Eumetazoa is the phylum Cnidaria which has the following characteristics:
• a diploblastic body plan with radial symmetry
anemone jellyfish
• some are sessile while others are free floating & motile
• have single opening called a proctostome (“anal mouth”) through which food enters the gastrovascular cavity and waste passes out
Two Cnidarian Body Types
Cnidirians are either a sessile polyp (e.g., corals, anemones) or a motile medusa (e.g., jellyfish).
Proctostome
Polyp
Body stalk
Tentacle
Tentacle
Epidermis
Mesoglea
Gastrodermis
Gastrovascular cavity
Medusa
Proctostome
Cnidarian Feeding
Cnidarians are carnivores that use tentacles to capture prey. Tentacle
Cuticle of prey
Nematocyst
“Trigger”
Thread discharges
Cnidocyte
Thread (coiled)
Thread • each tentacle has multiple
cnidocytes which contain a nematocyst, a specialized organelle that ejects a stinging thread when stimulated
2 Major Cnidarian Clades
MEDUSOZOA
Medusozoans
Anthozoans
Jellies Sea wasp
Sea anemones Star corals
• includes Scyphozoans (jellies), Cubozoans (box jellyfish), and Hydrozoans, all of which are medusae though some have a polyp stage in their life cycle (e.g., the Hydrozoans)
ANTHOZOA
• this clade includes the corals and anemones, all of which are polyps
Life Cycle of the Hydrozoan Obelia Haploid (n)
Diploid (2n)
Feeding polyp
Reproductive polyp
Medusa bud
ASEXUAL REPRODUCTION
(BUDDING)
SEXUAL REPRODUCTION
Medusa
Gonad
Egg Sperm
MEIOSIS
FERTILIZATION
Zygote Planula (larva)
Developing polyp
Mature polyp
Portion of a colony of polyps
1 m
m