1.
Survey of Lower Invertebrates
Phylum Porifera
&
Phylum Cnidaria
(Domain Eukaryota, Kingdom Animalia)

2.
Phylum Porifera (Sponges)
Etymology: From the Latin porus for pore and Ferre to bear,
hence an animal with pores.
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

3.
Phylum Porifera
(Sponges)

4.
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.

5.
Porifera Structures

6.
Porifera Structures
Asconoid Syconoid Leuconoid
Simplest body Intermediate Most complex
form complexity
(flagellated (flagellated (flagellated
spongocoel) canals) chambers)

7.
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)

8.
1. Class Calcarea
Calcareous spicules or more commonly, non-spicular calcareous porous
chambers

9.
2. Class Hexactinellida
Often called glass sponges. Siliceous (glass) spicules that are commonly fused to
form a net or box-like pattern

10.
3. Class Demospongea
Skeletons of spongin, spongin and siliceous spicules, or a skeleton of fused
opaline silica

11.
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

12.
Phylum Cnidaria
(Jellyfish, Corals, Anemonies, Hydras)

13.
Phylum Cnidaria (Jellyfish, Corals, Anemonies, Hydras)
Etymology: from Latin “cnida”, Greek “knide” for "nettle,"
from stem of knizein "to scratch scrape”, hence a
phylum of stinging invertebrates.
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

14.
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/

15.
Cnidaria Structure

16.
Cnidaria Taxonomy
1. Class Hydrozoa – hydras
2. Class Anthozoa – Corals, Anemonies
3. Class Scyphozoa – Jellyfish
4. Class Cubozoa – Box Jellyfish / Sea
wasps

17.
1. Class Hydrozoa –
Ex. hydras

18.
2. Class Anthozoa –
Ex. Corals, Anemonies, Sea Fan

19.
3. Class Scyphozoa –
Ex. Jellyfish

20.
4. Class Cubozoa –
Ex. Box Jellyfish / Sea wasps