Invertebrates: Sponges to Annelids Overview

Sponges

Phylum Porifera; habitat: fresh and marine waters, sessile; germ layers: none; no true tissues; body cavity: no; symmetry: asymmetrical; nervous system: none, no cephalization; gas exchange and excretion: diffusion; reproduction: most sponges are hermaphrodites; dispersal: flagellated, swimming larva.

Spongocoel

Cavity in sponges where water is drawn through pores and out through an opening called the osculum.

Choanocytes

Flagellated collar cells in sponges that generate a water current.

Amoebocytes

Cells in sponges that take up food particles, digest them, and carry nutrients to other cells.

Eumetzoa

Animals with true tissues; all animals except sponges and a few other groups belong to the clade Eumetazoa.

Cnidarians

Oldest Eumetazoans; phylum Cnidaria includes jellyfish, hydra, coral, and sea anemone.

Cnidarian Habitat

Marine and fresh water; includes sessile and motile forms.

Germ Layers in Cnidarians

Diploblastic, consisting of endoderm and ectoderm only.

Symmetry in Cnidarians

Radial body plan.

Body Cavity in Cnidarians

None.

Body Plans in Cnidarians

1) Sessile asexual polyp; 2) Sexual motile medusa.

Nervous System in Cnidarians

No cephalization, no brain; a non-centralized nerve net allows cells to communicate over long distances.

Nematocysts

Specialized stinging cells on the tentacles of cnidarians.

Cnidarian Feeding

Carnivores that use tentacles with nematocysts to capture and ingest prey.

Digestive System in Cnidarians

Incomplete digestive system with a single opening that functions as both mouth and anus; sac with a digestive compartment called gastrovascular cavity.

Gas Exchange in Cnidarians

By diffusion; cavity is only 2 cells thick.

Bilateria

Organisms with bilateral symmetry and triploblastic structure.

Lophotrochozoans Characteristics

Bilateral symmetry and 3 germ layers (triploblastic); some have lophophore for feeding; others pass through a trochophore larval stage.

Platyhelminthes

Flatworms; habitat: marine, fresh water, and damp terrestrial environments; can be free-living or parasitic.

Body Cavity in Platyhelminthes

None; Acoelmates.

Germ Layers/Symmetry in Platyhelminthes

Triploblastic/Bilateral.

Gas Exchange in Platyhelminthes

Very thin bodies; transport via diffusion; no circulatory system.

Nervous System in Platyhelminthes

Yes; nerves with a centralized 'brain'.

Cephalization in Platyhelminthes

Yes.

Head

Has light-sensitive eye spots

Digestive System

Gastrovascular cavity (one opening); branching delivers food to worm's cells

Platyhelminthes

Some free-living and some parasites

Planaria

Freshwater predators/scavengers that move with cilia or muscles

Tapeworms (cestodes)

Mostly parasitize vertebrates and attach to intestinal lining of host to obtain nutrients

Rotifers

Phylum: Syndermata = Rotifers; Protostomes with a body cavity (pseudocoelmates) and an alimentary canal

Mollusca

Includes snails, slugs, oysters, clams, octopuses, and squids; mostly marine, some freshwater & terrestrial

Mollusca Body Plan

Soft-bodied, but most secrete a hard shell; body cavity: Coelmates (hemocoel)

Radula

Organ that scrapes up food in molluscs

Circulatory System in Mollusca

Open (except cephalopods) with hemolymph as the circulatory fluid

Gas Exchange in Mollusca

Occurs through gills or simple lung

Digestive System in Mollusca

Scavengers with a digestive gland containing enzymes

Nervous System in Mollusca

Nerve ring around esophagus with nerve cords and cephalization

Excretion in Mollusca

Excretion organs present

Reproduction in Mollusca

Most have both sexes; snails are hermaphroditic

Mollusca Major Groups

Gastropoda (snails and slugs), Bivalvia (clams, oysters, and other bivalves), Cephalopoda (squids, octopuses, cuttlefish, and chambered nautiluses)

Cephalopoda

Active marine predators with a closed circulatory system, complex brain, and well-developed sense organs

Annelida

Segmented worms found in marine & freshwater and damp soil; coelomates and protostomes

Annelida Orders

1) Sedentaria (burrowers) 2) Errantia (swimmers, crawlers)

Leeches

Mostly freshwater predators & parasites that secrete hirudin to prevent blood coagulation

Earthworms

Class: Oligochaetes; have a complete digestive system and extract nutrients from soil

Gas Exchange in Annelida

Occurs through diffusion across skin

Excretion in Annelida

Nephrostome removes nitrogenous waste

Circulatory System in Annelida

Closed with blood

Reproduction in Annelida

Hermaphrodites that cross-fertilize

Lophotrochozoan

Includes two more phyla: Ectoprocta and Brachipoda, which have lophophores for feeding

Body Cavity in Lophotrochozoans

Yes! Coelomates

Deuterostomes

A classification that includes certain phyla of Lophotrochozoans