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