Simple Animals: Invertebrates



Invertebrate: Does not have a backbone
These invertebrates have simple digestive system, nervous systems and their
skeletal and muscular systems are very primitive or non existent
What are we going to be studying:
 Sponges
 Cnidarians: hydras, jellyfish
 Flatworms/Roundworms: Planaria, Tapeworms, Ascaris
 Annelids- segmented worms: Leeches, Earthworms (dissection)
 Mollusks: clams, squid, snails (possible squid dissection)
 Arthropods: insects, spiders, crustaceans
 Echinoderms: starfish, sea stars, sea urchins (starfish dissection)
Phylum Porifera: Sponges






Asymmetrical
Most are marine
They have no organ systems and are characterized by
numerous canals and chambers that open to the
outside by way of pores
Phylum names means: “pore-bearer”
Sessile: does not move
Filter feeders
Sponge Anatomy
water flows into the sponge - water flows into a sponge through cells with pores
(these cells arecalled porocytes) located all over its body.
water flows out of a sponge through large openings called oscula (plural). Each of
these large openings is called an osculum
A. Three Classes (tiger book pg 638)
1. Class Demospongae- General Structure. This is the largest of
the sponge classes. Bath sponges, which lacks calcareous or siliceous
spicules and is therefore soft to the touch. Most of the large pores
on the outer surface of this sponge are oscula (the excurrent
canals). The tiny pin holes on the surface represent, for the most
part, the ostia (incurrent canals).
Contain spongin; flexilbe protein fiber
Spongin
Spicules
Cross section of a commercial
sponge. Note the large
excurrent canals.
Halichondria
panicea Breadcrumb
Sponge
2. Class Hexactinellida (Hyalospongiae). These sponges have their
skeletons formed from silicon oxides (called spicules) which
gives them a glassy appearance (their common name is "glass
sponges"). Nearly all are deep-water forms, living at depths
between 200 and 1000 m.
Glass sponge spicules
Venus Flower Basket
3. Class Calcarea (Calcispongiae).
-- Memebers of the group Calcarea are the only sponges
that possess spicules composed of calcium carbonate.
-- Their diversity is greatest in the tropics, as is the case
with most marine groups. They are predominantly found in
shallow waters, though at least one species is known from a
depth of 4,000 meters.
A.
Reproduction
Both sexually and asexually
1. Asexually: regeneration. Each piece that is cut off will
attach and grow into a new sponge. Therefore, sponges use
this to reproduce; fragments of their body (buds) are broken
off by water currents and carried to another location, where
the sponge will grow into a clone of the parent sponge (its
DNA is identical to the parent's DNA).
2.
Sexually: Most sponges are hermaphrodites (each adult can
act as either the female or the male in reproduction).
Fertilization is internal in most species; some released sperm
randomly float to another sponge with the water current. If a
sperm is caught by another sponge's collar cells
(choanocytes), fertilization of an egg by the traveling sperm
takes place inside the sponge. The resulting tiny larva is
released and is free-swimming; it uses tiny cilia (hairs ) to
propel itself through the water. The larva eventually settles
on the sea floor, becomes sessile and grows into an adult. (pg
639)
Food

Sponges are filter feeders:
Most sponges eat tiny, floating organic particles and
plankton that they filter from the water the flows
through their body. Food is collected in specialized
cells called choanocytes and brought to other cells by
amoebocytes.
Vocabulary
1.
archaeocytes (amoebocytes) - Cells with pseudopods, located in the
mesohyl. They are used in processing food, distributing it to other
cells, and for other functions.
2.
choanocyte - also called collar cells, choanocytes line the inner cavity of the
sponge. They have a sticky, funnel-shaped collar (that collects food
particles) and a flagellum (which whips around, moving water). The sponge
obtains its nutrients and oxygen by processing flowing water using
choanocytes. Choanocytes are also involved in sponge reproduction; they
catch floating sperm.
3.
epidermis (pinacocyte) - the epidermis is the layer of cells that covers the
outer surface of the sponge. The thin, flattened cells of the epidermis are
called pinacocytes.
4.
5.
6.
Holdfast (base) - root-like tendrils that attach the sponge to rocks.
mesohyl (mesenchyme) - the gelatinous layer between the outer body of
the sponge and the spongocoel (the inner cavity).
osculum - a large opening in a sponge through which water flows out of the
sponge. Sponges may have more than one oscula.
7. ostia - a series of tiny pores all over the body of a sponge that let
water into the sponge. One of these is called an ostium
8. pinacocyte - pinacocytes are the thin, flattened cells of the
epidermis, the sponge's outer layer of cells.
9. porocyte - cells with pores that allow water into the sponge; they are
located all over the sponge's body.
10. sessile - permanently attached to a substrate and unable to move
on its own. Adult sponges are sessile.
11. spicule - spicules are sharp spikes (made of calcium carbonate)
located in the mesohyl. Spicules form the "skeleton" of many
sponges.
12. spongin - the flexible, fibrous fibers that form the skeleton of horny
sponges; spongin is located within the mesohyl.
13. spongocoel - the central, open cavity in a sponge through which
water flows.