Fussmann Combined

Species (phylogenetically)

The lowest taxonomic unit with uncontroversial membership.

Nodes represent _______ in a phylogeny.

Taxa

Lines represent _______ in a phylogeny.

Descent

Monophyletic group (synonym and definition)

Also known as a clade; a group of organisms with a single common ancestor, defined by shared derived character traits.

Metazoa

Term for animals.

Two objectives of phylogeny

A. To understand how one kind of animal evolves from another.

B. To discover the relationships between the kinds of animals

Classically, A is used to find B, but with molecular data, the opposite can happen.

Phylum

A monophyletic group that comprises animals of the same fundamental body plan. Classification of phyla continues to be controversial

What are animals?

Motile multicellular organisms with somatic differentiation (usually).

Traits:

• Multicelluar

• Heterotropic

• Nervous System (arises later in the phylogeny)

• Mobile stages

• Cell differentiation

• Blastula stage

Choanoflagellata

• Sister taxon of Metazoa

• Single flagellum

• Base of flagellum is surrounded by collar of actin filaments (microvilli)

• Flagellar movement draws water through the collar, trapping edible particles (i.e. bacteria)

• May be free-swimming or sessile.

• Sessile forms tend to be colonial - connected with an ECM - likely resembles ancestral Porifera

• Resemble choanocytes found in Porifera

Choanocytes

Porifera cell type, resemble Choanoflagellata.

Have the same general cell structure, Microvilli collar

Metazoan traits

Epithelial cells

Mesenchymal cells

Epithelial cells

• Polarized

• Arranged in parallel

• Basement membrane

• Joined by belt-form junctions

Mesenchymal cells

• No particular alignment with other mesenchymal cells

• Bear only spot-form junctions

• Surrounded by ECM

The blastula

• Ball of hollow cells

• Comes from equal radial cleavage

• 2 main difficulties: Cannot feed (no mouth, cannot further develop because of ciliation (if cilia were shed, the embryo would sink).

• Solution=gastrulation

Gastrulation

Fundamental feature of metazoans,

Cells on the interior can divide/ differentiate without compromising motility.

Five known clades of Metazoa

Porifera (sponges)

Placozoa (“flat animals”)

Cnidaria (jellyfish, corals, hydroids, etc)

Ctenophora (comb jellies)

Bilateria (everything else

Placozoa

“Ciliated plates”

• Single known species

• Up to 2 mm size

• Global distribution in littoral of tropical and subtropical oceans

• Development only observed up to 64 cells

Placozoan anatomy

Simpler organization than any other living metazoan:

• Sandwich organization: Upper and lower epithelium with loose network of fiber cells

• No mouth, organ systems, nerve or muscle cells

• No symmetry of any kind

• Irregular body shape, constantly changes

Placozoan feeding

Moves on surfaces via ciliary creeping

Feeds by overlaying an algal cell and lysing it with extracellular digestive enzymes.

Grades of organization in metazoa

Non-epithelial (incomplete compartmentalization):

• Porifera

• Placozoa

Epithelial diploblasts:

• Cnidaria

Epithelial triploblasts:

• Bilateria

Choanocyte

Uniflagellate cell with a collar of microvilli.

Draws water through the collar

Retains particles larger than 0.2 micrometers (ex. bacteria)

Ingests particles via phagocytosis, transfers to Archaeocytes for digestion

Each choanocyte captures ~ 3-4 bacteria every day.

Archaeocytes/ Amoebocytes

Porifera cells that digest bacteria

Totipotent cells

Found in mesohyl

Porocytes

“Doughnut-shaped” cells

Form pores through which water is drawn into the sponge

Bridge the mesohyl

Spongocoel

Interior of the sponge

Pinacoderm

Outer layer of protective cells in sponges.

Not real epithelium

Mesohyl

Gelatinous layer between pinacoderm and choanocyte chambers

Contains archaeocytes

Spicules

Porifera structure and protection

Made of calcite, silicate, or protein

Distributed in mesohyl

Give shape to sponge body

Often characteristic to species

All Porifera cell types:

• Choanocytes

• Pinacocytes

• Archaeocytes

• Porocytes

Osculum

Opening of the spongocoel

Asconoid Body Plan

Found in Porifera

Simplest body plan

Choanocytes arranged on spongocoel walls

Syconoid Body Plan

Folded inner wall

• Increased surface area for choanocytes

• Increased power of water flow

• Allows for larger individuals

Leuconoid Body Plan

Folded folds create chambers:

• Allows sponges to grow to 1m+ size

Vegetative Propogation (Sponges)

Budding, branching, fragmentation possible

Freshwater sponges survive winter as reduction bodies called gemmules

Sexual Cycle (Sponges)

• No discrete gonads

• Ova and sperm develop from somatic cells

• Most sponges are hermaphroditic

• Sperm are released en masse into the water

• Sperm are then phagocytosed by choanocytes of neighbouring individuals

• Then de-differentiated into ameboid carrier cells

• Migrate into mesohyl and fertilize oocytes

Sponge Development

Wide range of development

• Cleavage is usually total and equal (no order/ size differentiation)

• Late blastulae experience extensive cellular reorganizations

• Homology of developmental processes in sponges with gastrulation and germ layer formation in other metazoans uncertain

Sponge life cycle

• Small, ciliated pelagic larve

• Metamorphosis into benthic adult

• Lecithotrophic larvae (feed on maternally supplied yolk)

Lecithotrophic larvae

Larvae that feed on maternally supplied yolk

Planktotrophic larva

Rely on external food sources

Sponge symbionts

• Wide variety of symbiotic microbes in the mesohyl

• Up to 30% of the wet weight of sponges

• Some (e.g. cyanobacteria) are mutualists

Carnivorous sponges

Demosponges in the family Cladhorizae can capture living prey (i.e. shrimp)

Use hooked spicules

Most live in deep water (below 1000m) or in caves

Some retain chambers and choanocytes

Others have lost their choanocytes

Calcarea (Calcispongiae)

• Sponge clade

• Sister group of Homoscleromorpha

• 3-4 radiate spicules made of calcium carbonate

• Mostly small, drab, inconspicuous

• Simple asconoid or syconoid body plans

• ~ 400 species

Homoscleromorpha

• Porifera clade

• Sister group of Calcarea

• Reduced skeleton of uniform siliceous spicules (without axial filament)

• Epithelium with basement membrane and specialized cell junctions

• Possibly branched later than other Porifera

Demospongiae

• Porifera clade

• Sister group of Hexactinellida

• Siliceous spicules organized around an axial filament (shared with Hexactinellida)

• Spicules not with six rays

• Spongin network often present

• Mostly complex leuconoid body plan

• Ocean and freshwater

• Includes carnivorous sponges

• All of the really big sponges

Hexactinellida

• Porifera clade

• Sister group of Demospongiae

• Siliceous spicules organized around an axial filament (shared with Demospongiae)

• Rigid skeleton of 6-pointed siliceous spicules

• Syncytial network of soft body tissue

• “Collar bodies” instead of “collar cells”

• Deep-water forms

• Most common in cold seas, especially the Antarctic

Porifera groups summary sheet

Classes of Cnidaria

Three classical classes

• Anthozoa: Corals and anemones

• Scyphozoa: Jellyfish

• Hydrozoa

Two additional classes:

• Staurozoa: Stalked jellyfish

• Cubozoa: Box jellyfish

Anthozoa

Cnidarian class

Subclasses:

• Hexacorrallia

• Octocorrallia

Most corals and sea anemones

Polyp only - completely suppressed medusa

Includes reef-building corals with massive calcareous exoskeleton for zooids

Medusozoa

Cnidarian class

Sister group of Anthozoa

Contains 2 sister groups:

• Staurozoa (stalked jellyfish), Scyphozoa (jellyfish), Cubozoa (box jellyfish)

• Hydrozoa

Cnidarian Characteristics

Diploblastic:

• Ectoderm and Entoderm

Oral-aboral axis and radial symmetry

Life Cycle:

• Ciliated Planula larvae

• Polyp (asexual) and Medusa (sexual) - with variations and reductions

Solitary or colonial

Tentacles

Neurons → nerve net

Musculature

Simple sensory structures (more complex in some Cubozoa

Parasitic Myoxozoa have virtually none of these characteristics

Myoxozoa

Parasitic Cnidarians, have virtually no typical traits

Cnidarian germ layers

Ectoderm → Epidermis

Endoderm → Gastrodermis

Mesoglea between layers

Mesoglea

Between epidermis and gastrodermis in Cnidarians

Zooid

An animal arising from another through budding or division, especially in each of the organisms of a colony.

• Ex: The hydrozoan polyp

Hydrozoan development

Cleavage:

• Equal and radial

• Blastula → Gastrula → Planula

Ciliated Planula larvae

• Cnidarian larvae

• Ciliated ectoderm and solid endodermal mass

• Cellular differentiation (nerve, muscle, sensory and gland cells, nematocysts)

• Feeds in anthozoans, but not hydrozoans

• Planula attaches at the aboral end and becomes a polyp, developing mouth and gastric cavity

Cnidarian colonies

• Budding and persistent stolon lead to colonies

• Differentiation leads to polymorphic colonies

• Ex: Hydractinia

Hydractinia

A colonial hydrozoan growing on gastropod shells

Several kinds of morphologically/ functionally distinct zooids:

• Gastrozooid

• Gonozooid

• Dactylozooid

Gastrozooid

Colonial zooid type found in Cnidarian Hydractinia

Feeding zooid with mouth, tentacles, and gastric cavity

Gonozooid

Colonial zooid type found in Cnidarian Hydractinia

Reproductive zooid that forms sexual medusa

Dactylozooid

Colonial zooid type found in Cnidarian Hydractinia

Protective zooid with nematocysts but no mouth

The Hydrozoan medusa

• Motile zooid

• Swims by contraction of muscular ring

• Sexual zooid, bearing gonads - some budding occurs, but rarely

• Gametes shed directly into seawater, fertilization is usually external

The cnidocyte

Perhaps the most complicated of all metazoan cell types

Discharge stimulated by chemical (prey body fluids) and mechanical (displacement of cnidocil) signals

Coral zooids

Anthozoa (Cnidaria)

Form large non-polymorphic colonies

Nematocyst-armed tentacles

Usually rely on endosymbiotic zooxanthellae for most of their metabolism

Each zooid occupies a cup on the surface of the block of secreted calcium carbonate

Gorgonacea

Anthozoa (Cnidaria)

Sea whips and sea fans

Pennatulacea

Anthozoa (Cnidaria)

Soft corals and sea pens

Scyphozoa

Traditional Cnidarian class

Jellyfish

Primarily predatory marine medusae

Highly reduced polyp phase

~ 200 species worldwide

Tetramerous symmetry

Bell with motile tentacles or drawn out into 4 oral arms

Capture prey with nematocysts on tentacles, arms, and bells

Mesoglea contains fibres and ameboid cells, often stiff

Swimming by jet propulsion

Sensory organs on periphery of bell - Rhopalia

Rhopalia

Scyphozoan sensory organ

• Contains statocyst, ciliated sensory pit, and sometimes ocelli

Scyphozoan development

• Solid or hollow ball develops into a polyp, the scyphistoma

• Immature medusae (ephyrae) bud from polyp by horizontal fission (strobilation)

Cubozoa (Cubomedusae)

• Box jellyfish- cuboidal bell with 4 flattened sides

• Tentacle or bunch of tentacles at each corner

• Rhopalia, containing large, complex, lens-bearing eye

• Active predators of fish

• Highly venemous

Hydrozoa

Most marine, colonial, with typical life cycle

Ex: Portuguese man-of-war

Ctenophora

Marine predators

200 species, mostly pelagic

>1 cm to 2 m

Shared with Cnidaria:

• Diploblasts with Mesoglea

• Oral-aboral axis with radial symmetry

• Gelatinous body

• Tentacles

• Nerve and muscle cells

Unique traits

• 8 rows of ctenes (comb-like, ciliated plates)

• Colloblasts (adhesive cells)

• Statocyst-based sensory organ

• Bioluminescence is common

Ctenophore general anatomy

Ectoderm + entoderm, separated by mesoglea

Muscle cells in mesoglea

Epidermal body wall with basement membrane

Mouth → Blind gut → anal pores

Comb rows (ctenes)

Comb = blade of fused cilia

Beat in sequence for propulsion

Ctenophores= larges animals propelled by cilia

Ctenophore tentacles

Paired

Capture prey with colloblasts

Different from cnidarian tentacles, may have evolved separately

Colloblasts

Adhesive cell used by Ctenophores to capture prey

Ctenophore nervous system

Neurons with synapses

Nerve net with some neural concentrations

Lack many bilaterian genes for neural developments and neurotransmission

Possibly evolved independently

Apical organ

Complex statocyst-based organ at the aboral pole

Senses gravity and controls movement, including ciliary beating

Flattened Cestida (“Venus girdle”

Ctenophore example

Benthic Platyctenida

Ctenophore

Settles of sea stars

Tentacles and colloblasts

Predatory Beroida

Ctenophore

8 comb rows

No tentacles

Mnemiopsis leidyi (“Sea Walnuts)

• Invaded Black Sea in the 1980s

• Introduced from North America through ballast water

• Feeds on zooplankton and fish larvae

• Disrupted whole ecosystem

Current consensus view on Bilateria Phylogeny

Bilateria

Bilateral symmetry at some life stage

Triploblastic

• Mesoderm → Muscles

• Mesoderm → Coelom

Bilateral symmetry

Two mirrored portions - left & right

Typically accompanied by cephalization

Three planes

• Anterior - posterior

• Dorsal - ventral

• Medial - lateral

Acoelomates

e.g. Acoela, Platyhelminthes

Pseudocoelomates

e.g. Nematoda

Coelomates

e.g. Annelida

Protostome Developmental Tendency

Spiral Cleavage

Mosaic Embryo

Blastopore becomes mouth

Coelom forms by splitting (Schizocoelus)

Deutorostome Developmental Tendency

Radial Cleavage

Regulative Embryo

Blastopore becomes anus

Coelom forms by outpocketing (enterocoelus)

Xenacoelomorpha

• a.k.a Acoela

• Acoel flatworms

• Formerly grouped in Platyhelminthes

• Sister group of all other Bilateria

• 3 internal sister clades

• Marine worms

• Examples:

  • Xenoturbellida

  • Amphiscollops

Spiralia

• Protostome clade characterized by spiral cleavage

• = Lophotrochozoa

• Sister group of Ecdysozoa

Spiral Cleavage

3rd division is unequal:

• 4 macromeres

• 4 micromeres

Subsequent divisions also unequal

Result:

• A hollow, ciliated blastula that develops into a prototroch larva

Current consensus phylogeny of Spiralia

Gnathifera

Gnathostomulidae and Rotifers

Sister group of Chaethognaths

Chaetognatha

“Arrow worms”

Marine, ~100 species

Abundant planktonic ambush predators - up to 10% of plankton biomass

Torpedo-shaped, 1-12 cm

Trunk with “fins”

Mouth with grasping spines and “teeth”

Chaetognath anatomy

Lateral fins for swimming

Chitinous spines for capturing prey

Body usually turgid with a well-developed coelom

Gnathostomulidae

Sister group of Rotifera, part of Gnathifera

Marine and brackish worms, up to 3 cm

Acoelomates

Complex jaws

Rotifera

Mostly free-living, freshwater, microscopic; ~ 2000 species (plus ~1500 in Acanthocephala)

Corona of cilia (rotary or wheel organ)

Feeding apparatus with muscular mastax and trophi (“jaw”)
“Toes”

Pseudocoelomate

Eutely; syncytial epidermis

Cryptobiosis common

Reduction of male sex common

Rotifer anatomy

Body wall: Cuticle, epidermis, and subepidermal muscles

Syncytial epidermis with scattered nuclei

Spacious body cavity, pseudocoel

No respiratory or circulatory systems