Invertebrates 1 Introduction, Porifera, Cnidaria

Lecture outline 1.Overview: Invertebrate lectures 2.What is an animal? 3.Introduction to major phyla in Kingdom Animalia 4.Basic phylogeny of Kingdom Animalia 5.Phylum Porifera 6.Phylum Cnidaria

1. Overview of Invertebrate portion of course  Evolutionary relationships  Body plan  How animal meets its basic needs  Relationship of structure and function  Selected aspects of life-history and ecology

2. What is an animal?  Eukaryotic  Multicellular: Multiple cell types (Not just many cells)  Heterotrophic  No cell wall  Characteristics of early development (unique!)  Blastula and gastrula stages unique to animals  Sponges, have precursors to these stages

Phylum Porifera: sponges

Phylum Cnidaria: Have Cnidocytes

Phylum Ctenophora: The comb jellies

Phylum Platyhelminthes: The flatworms

Phylum Nematoda: The roundworms

Phylum Annelida: The segmented worms

Phylum Mollusca: The “soft-bodied” animals

Phylum Arthropoda: Jointed appendages

Phylum Echinodermata: Spiny-skinned

Phylum Chordata: Animals with notochords

4. Phylogenetic overview  Presumed to be monophyletic  Hypothesis assumes all animals evolve from a single common ancestor  That ancestor thought to be a sponge-like protist called a choanoflagellate  Modern choanoflagellate  Found in aquatic habitats  Some propose polyphyletic origins polyphyletic origins  Cite Cambrian explosion

Phylogenetic overview (“traditional”)

Multicellularity separates the ancestral protists from all animals  Multicellularity  Different types of cells!

Development of two true tissue layers  Separates Phylum Porifera from all others  Sponges All other groups (2-3 tissues)

Development of a third germ layer and bilateral symmetry  Cnidarians, Ctenophores All others  Radial symmetry, 2 layers Bilateral symmetry, 3 layers  (Porifera)

Further developments (briefly)

Body cavities  Acoelomate  Pseudocoelomates  Coelomates

Further developments (briefly)

5. Phylum Porifera: The sponges

Evolutionary relationships  Simplest multicellular animals  Main cell type, choanocyte, resembles choanoflagellate cell  Considered "multicellular" rather than colonial, because there are different cell types.  Not much, if any cooperation between cells  No real "tissues", no "systems" of any type (no nervous system, circulatory system, etc.)

Sponge structure  Review key parts…

Water movement and feeding  Role of flagellum  Role of collar  Movement of particles  Phagocytosis

Protection  Sponges are sessile…  Toxins/warning coloration (this is why many sponges are brightly colored)  Painful or sharp covering (spicules)  Regenerative ability  Camouflage (if not toxic)  Bore into shells.  NOTE: Nudibranch predators co-opt sponge defenses (toxins, spicules)

Phylum Cnidaria

Evolutionary relationships  Diverge from the Porifera in the following ways:  Diploblastic: two true tissue layers  Ectoderm and endoderm  No mesoderm  Radiata: One of two phyla to exhibit radial symmetry

Where Cnidarians fit in…  Cnidarians, Ctenophores All others  Radial symmetry, 2 layers Bilateral symmetry, 3 layers  (Porifera)

Body organization  Polyps and medusae

Key features  Polyps and medusae  Tissue layers  Ectoderm, gastroderm (=endoderm)  Mesoglia  Secreted from the tissue layers  Gastrovascular cavity  Functions  Not a true body cavity!  Nervous system: nerve net  No other major body systems  Tentacles with cnidocytes (stinging cells)

Nervous system features   True neurons   Conduction can be unidirectional or bidirectional along neurons   Nerve net with no direct pathways   Have simple sensory organs

Cnidocytes/nematocysts How do they work?

Life-history strategies