Survey of Lower Invertebrates

Phylum Porifera

&

Phylum Cnidaria

(Domain Eukaryota, Kingdom Animalia)

Phylum Porifera (Sponges)

Key Characteristics:

• Simplest members of Kingdom Animalia

• Multicellular, no tissues or organs

• Mostly asymmetrical

• Acoelomates

• Sexual or asexual,

• Adults are sessile, zygotes are protozoan-like.

• Live in aquatic environments

Etymology: From the Latin porus for pore and Ferre to bear, hence an animal with pores.

Phylum Porifera

(Sponges)

Porifera Structures• Spicule – Skeletal component. Provides structure & support for the

cells.

• Osculum – Large pore where water escapes from sponge.

• Spongocoel (Atrium) – Open space inside sponge.

• Choanocyte – (collar cell) goblet shaped cells w/ flagellum that line the inside of sponges and capture food.

• Amoebocyte – amoeba-like cells that travel along the spicules and absorb food.

• Pinacyte – outer epidermis of sponge.

• Porocyte & Myocyte – muscle-like cell surrounding pores that expand & contract to control water flow into the sponge.

• Mesohyal (Mesophyl) – Center layer of sponge, between outer and inner layers.

Porifera Structures

Porifera StructuresAsconoid

Simplest body form(flagellated spongocoel)

Syconoid

Intermediate complexity(flagellated

canals)

Leuconoid

Most complex

(flagellated chambers)

Porifera Taxonomy

1. Class Calcarea - Calcium sponges

2. Class Hexactinellida - Glass sponges

3. Class Demospongiae - Spongin (soft) sponges

Fossils Only:

4. Class Stromatoporoida (Ordovician)

5. Phylum Archaeocyatha (Cambrian)

1. Class CalcareaCalcareous spicules or more commonly, non-spicular calcareous porous

chambers

2. Class HexactinellidaOften called glass sponges. Siliceous (glass) spicules that are commonly fused to

form a net or box-like pattern

3. Class DemospongeaSkeletons of spongin, spongin and siliceous spicules, or a skeleton of fused

opaline silica

Fossil Sponges:• Class Stromatoporoida

Some paleontologists consider this group a member of demospongea, some

do not consider them as true sponges, but belonging to their own

phylum.

• Phylum Archaeocyatha Predominantly an Early Cambrian phylum with no living representatives

Phylum Cnidaria

(Jellyfish, Corals, Anemonies, Hydras)

Phylum Cnidaria (Jellyfish, Corals, Anemonies, Hydras)

Key Characteristics:

• Nematocysts – stinging cells

• Sac-like Diploblastic Body – formed from two germ layers, endo & ectoderm.

• tissue level of organization

• radial symmetry

• All have sessile phase

Etymology: from Latin “cnida”, Greek “knide” for "nettle," from stem of knizein "to scratch scrape”, hence a phylum of stinging invertebrates.

Life Cycle of Select Cnidarians

Figure 7. Life cycle of Obelia showing an alternation between the polyp (asexual reproduction) and medusa (sexual reproduction). This life cycle is typical for many species in Class Hydrozoa. Class Schyphozoa emphasizes the medusa stage while Class Anthozoa has only polyps. Modified diagram courtesy of BIODIDAC (University of Ottawa), http://biodidac.bio.uottawa.ca/

Cnidaria Structure

Cnidaria Taxonomy

1. Class Hydrozoa – hydras

2. Class Anthozoa – Corals, Anemonies

3. Class Scyphozoa – Jellyfish

4. Class Cubozoa – Box Jellyfish / Sea wasps

1. Class Hydrozoa – Ex. hydras

2. Class Anthozoa – Ex. Corals, Anemonies, Sea Fan

3. Class Scyphozoa – Ex. Jellyfish

4. Class Cubozoa – Ex. Box Jellyfish / Sea wasps