The Metazoa (Differentiated Multicellular Animals) An Overview of the Major Groups How Do We Classify Life ?

Note: Kingdoms Eubacteria and Archaea formerly classified as Kingdom Monera

Three Domains Now Three Domains and 6 Kingdoms

Archaea

Eukarya

Bacteria

1 Conventional Classification of Major Phyla Discovery of classic “Ediacaran Fauna” (about 543 Ma) Protista amoebas, foraminifera, radiolaria (presumed ancestors of Metazoa)

Metazoa Porifera sponges Cnidaria/Coelenterata sea anemones, corals, sea pens, etc. Several “worm” phyla flatworms, annelids, etc. Pound Quartzite Brachiopoda brachiopods (“lamp shells”) Ediacara Hills, north of Sydney, Australia Bryozoa bryozoans (“moss animals”) Metazoan Fossils Found in 1946 Mollusca snails, clams, cephalopods, etc. Arthropoda shrimps, crabs, insects, spiders, etc. Echinodermata starfish, sea urchins, crinoids, etc. Hemichordata acorn worms, graptolites, etc. Chordata lancelet, vertebrates, etc.

Classification: lumped together as “medusoids”

Details originally overlooked: A diverse assemblages of fossils Mistaken Point, Newfoundland 565 Ma

Mawsonites Spriggina

Dickinsonia “spindles”

2 Portugal Cove Newfoundland Up to about 575 Ma

Latest Proterozoic (Ediacaran Period) Oxygenated atmosphere and seas Complex, soft-bodied metazoa Charniodiscus (fronds)

Adolph Seilacher Were Vendian organisms Early representatives of modern phyla ? Concept of “Vendozoa: (Extinct phylum ? Probably not.)

Sea Pen Nudibranch

soft bodied “quilted” structure (fluid-filled bags ?” Dependent on microbial mats “mat stickers”: fixed to seafloor, photosynthesizers “mat scratchers”: grazed on microbial mats

Ostrich plume hydroid No carnivores !

3 How do You Make a Metazoan ? You Have to Start Out Simple. Phylum Protista: the importance of choanoflagellates Single celled Protista

A choanoflagellate is a protist with a collared cell and a flagellum

Amoebas, Foraminifera, Radiolaria, etc.

Some choanoflagellates form colonies

In such colonies, all individuals cooperate in moving their flagella, generating a current from which food particles can be extracted

On to the Metazoa…

4 Phylum Porifera (Sponges) Similar to some of the Ediacaran Most Basic Metazoan Plan of Cowen animals (remember the frond-like creatures), sponges show a fractal organization

Leucon-grade sponge (contains multiple “sycon” elements)

Single layer of tissue Sycon-grade sponge (collared cells) (contains multiple Sponges also have collared cells, but these form a larger, integrated structure supported by rigid spicules or organic tissue. The differentiation “ascon” elements) of cells required the evolution of Hox Genes (genes that dictate differing Ascon-grade sponge functions of cells)

Phylum Cnidaria / Coelenterata Phylum Cnidaria / Coelenterata (Second Metazoan Body Plan of Cowen)

Hydra hard corals sea pens

2 layers of tissue: ectoderm, endoderm sea anemones (probably resulted from invagination of ectoderm) soft corals jellyfish 2 tissue layers: ectoderm, endoderm

5 “Worms” or “Bilaterans” Most Complex Metazoan Body Plan of Cowen

Natural coral Computer-generated fractal triploblastic - 3 principal cell layers ectoderm, mesoderm, endoderm Again, in the more complex forms of these simple organisms fractal geometry is apparent Basic bilateral symmetry: fractal geometry breaks down, but tissue differentiation is incredible !

The Coelom Coelom and Orifice Development; Protostomes

In the Protostomes (including molluscs, annelid worms and arthropods), the coelom develops directly from mesodermal tissue.

Another distinguishing characteristic to the The Ectoderm and Endoderm can be viewed as essentially protostomes is the solid, continuous layers. development of the mouth The Mesoderm is a little more complicated in that it actually before the anus in the lines a fluid-filled body cavity called the coelom. It is within young embryo the coelom that internal organs other than the gut develop (e.g. respiratory organs)

6 Coelom and Orifice Development; The Evolution of the Coelom Deuterostomes

In the Deuterostomes The coelom may have initially evolved as a hydraulic device. (including echinoderms and chordates), the coelom A bilateran with a coelom can squeeze its internal fluids with develops from outpockets of body muscles. the gut (endoderm) This squeezing bulges the body wall at the weakest point, Another distinguishing and can be used as a “power drill” for burrowing (think about characteristic to the how a worm gets around). protostomes is the development of the anus before the mouth in the young embryo (blastophore)

The Evolution of the Coelom

In addition, this pumping could facilitate the transport of oxygen through the body without relying on the bathing of The Protostomes can be subdivided in two smaller groups tissues in oxygenated water by diffusion through a thin (clades): ectoderm. 1. Lophotrochozoa This means that animals could efficiently deliver oxygen 2. Ecdysozoa throughout their bodies without compromising the effectiveness of their outer skins (ectoderm) or size.

This also meant that animals could evolve exoskeletons.

7 Lophotrochozoa: This group gets its confusing name from two related subgroups (linked by molecular phylogenetic studies):

1. The trochozoa - animals with distinctive, fuzzy, trochophore Important Lophotrochozoans larvae, which include the phyla trochophore larva Platyhelminthes and the Mollusca.

2. The lophophora – animals which feed via a fringe of hollow Lophophore tentacles, called a lophophore), (in brachiopod) which include the phyla Brachiopoda and Bryozoa.

Lophotrochozoa: Phylum Platyhelminthes (flatworms) Lophotrochozoa: Phylum Mollusca

Flatworms do not have a coelom, and it is likely that Each class derived from HAM something like a flatworm gave rise to more advanced (hypothetical ancestral mollusc) coelomate bilaterans.

Key Features: gut mantle cavity radula (rasping organ) gills foot

8 Lophotrochozoa: Phylum Mollusca Lophotrochozoa: Phylum Brachiopoda (“arm foot”)

Gastropods Bivalves

Key Features: pedicle, gut, muscles, lophophore

Cephalopods (squids, octopuses, cuttlefish, ammonoids)

Lophotrochozoa: Phylum Bryozoa (“moss animals”)

Ecdysozoa: This group includes animals that moult Key Features: their outer covering colonial habit, lophophore as they grow. Phylum Arthropoda is the primary phylum of this group.

9 Ecdysozoa: Phylum Arthropoda

Insects Spiders Crabs Lobsters Important Ecdysozoa Barnacles trilobites eurypterids Etc.

Key Features: Jointed appendages 3-fold division of body (head, thorax, abdomen)

scorpions shrimps

Deuterostomia: Phylum Echinodermata (“spiny skin”)

Sea urchins Brittlestars Important Deuterostomes (Deuterostomia)

Crinoids

Starfish Sea cucumbers

Key Features: 5-fold symmetry, calcite plates (but embryos are bilateral, suggesting a bilateral ancestor)

10 Deuterostomia: Phylum Hemichordata Deuterostomia: Phylum Chordata

Key Features: Key Characteristics: notochord 3-part division of body Sea squirts and salps (Urochordates) dorsal nerve cord, (preoral lobe, collar, trunk) pharynx Pterobranchs Pharynx gills slits Gill slits post-anal tail Stomochord

Amphioxus (lancelet) Graptolites Acorn worms (Cephalochordates)

END OF LECTURE

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