77 terms

Understanding Animal Biology: Unit 4

Basal Metazoans

Terms in this set (...)

Endosymbiotic Origin
Association of bacteria, additional organelles & membrane processes
*Additional energetics
*Facilitated complexity
*Facilitated diversity

Specific order of symbioses uncertain
includes animals, fungi, and some protists
-Most protozoa, algae, plants
-DHFR + TS fused
fungi, choanoflagellates (protozoan), animals
"Posterior flagellum"
-E.g., sperm and spore flagellum

Include fungi, choanoflagellates & metazoa

Few unifying, discriminating characters
*Molecular data (proteins, rRNA) support relationship
-"Mouth first"
-Includes 2 major groups

*Trochozoa (annelids, molluscs, etc)
*Lophophorata (bryozoa, brachiopods, etc)

*The molters (arthropods, nematodes, etc)
Supergroup of protostomes; characterized by periodic molting of their exoskeleton. Include the roundworms and arthropods.
multicellular animals
Metazoan Characteristics
-Differentiated tissues
-Sexually reproducing
Major Metazoan Lineages
-Porifera (sponges)
-Placozoa (Trichoplax)
-Ctenophora (comb jellies)
-Cnidaria (jellyfish, corals, related)
-Bilateria (all other animal phyla) (contains majority of metazoan biodiversity)
How to Classify an Animal

Developmental Complexity
-Zygotic mitosis -> formation of blastula
-Blastula invaginates during gastrulation
Developmental Complexity
During gastrulation 2-3 layers of primary, pluripotent cells form
-Radiate animals are diploblastic
-Bilaterate animals are triploblastic

Germ layers -> organogenesis
Develop a coelom (body cavity)
-There may be phylogenetic value in

-True coelom arises from mesoderm

-Variations occur in some protostomes
*Pseudocoelom: M+En
*Acoelom: no coelom
Poorly defined tissues
-'near animals'
The basal animal group?
-Why basal
*Lack clear-cut germ layers
*Lack true tissues

-Possess differentiated cells
-Have many of the "developmental toolbox" genes
Porifera Diversity
-About 5,000-10,000 species
-All aquatic, >90% are marine
-Asymmetrical body plan
---Reflects environment
---Phylogenetic & skeletal constraints
Porifera Skeleton
Sort of...
-"Spicule" deposits provide support/rigidity

Deposited in the mesohyl
-Collagenous connective material
-Most common mesohyl material is called spongin
a needle of silica or calcium carbonate in the skeleton of some sponges
gelatinous matrix within a sponge
Flexible material that make up the skeleton of some sponges.
Porifera Groupings (major)
Development & morphology of internal canal system

Not really based on morphology
-Largely based on +/- skeleton, and...
-Spicule composition: CaCO3 vs SiO2
-Presence of spongin
Morphology (Porifera)
Immatures are motile

Adults are sessile
-So they bring things to themselves
-Morphology reflects this
-Some lab evidence of motility
Morphology (Porifera)
Lack true tissue.... Instead, 'cooperating cells!'
Energetics (Porifera)
Choanocytes create currents

All cells engage in phagocytosis, pinocytosis, and absorption

Archaeocytes may carry food to other cells

There's no division of labor to speak of
-All cells respire
-All cells excrete
Reproduction (Porifera)
Essentially all cells are totipotent stem cells
-Disaggregation experiments

Asexual reproduction by budding
-Internal (termed gemmules) - covered with spicules, i.e. tough
Reproduction (Porifera)
Sexual reproduction
Generally hermaphroditic
Archaeocytes/amoebocytes -> eggs
Choanocytes -> sperm
-Viviparity vs oviparity
Porifera Sensory Mechanisms
-Chemosensory proteins present
-Mechanosensory ability
-Have cryptochrome photopigments
-Lack a nervous system or even nerves
---Chemical communication...?
Represented by single species: Trichoplax adhaerens
-First identified in aquaria (1883)
-Marine, Diam: 2-3 mm, Thick: <200um
-No L/R or A/P symmetry
-D/V polarity
show high genetic variance

Single species: Trichoplax adhaerens
-Significant genetic variance
-Are there multiple species?
Placazoan Complexity
Several thousand cells

4 "classical" cells types
-Dorsal/Upper epithelial
---Flagellated (UE)
-Ventral/Lower epithelial
---Non-flagellated glandular (GC)
---Columnar cylindrical+flagellum (LE)
---Syncitial fiber cells (FC)
---Synapse-like attachments
---Symbiotic bacteria (B)

Gene expression suggests more complexity there
Placazoan Complexity
Appears to be diploblastic
Muscle & neural systems
Lack basement membrane
Encodes gene networks that suggest loss
Placazoan Energetics
Extracellular digestion
-Glandular cells secrete enzymes

Phagocytic 'ingestion'
-By ventral epithelial cells

Excretion from cells
Placazoan Reproduction

-Dividing in half

-Unequal separation and formation

-Produces multicellular, flagellated 'swarmers'
Placazoan Reproduction
-Typically observed only in lab
-Under stress typically
-Mother degenerates
---Small flagellated cells (sperm?)
---Bursting releases
Members of the radially symmetrical animal phyla, including cnidarians and Ctenophora.
Basal Metazoa (Who is it?)
-Some phylogenomic studies

-Other phylogenomic studies

Problems with determining ______________ _________________
-Complex traits (eg, nervous system) = 1 or many characters?
-Long branch attraction?
Cnidarian Diversity
Arose in Ediacaran (Vendian) period of Proterozoic
-Fossils found in 540-650 mya range
-A lot of Paleozoic diversity
-Wiped out at Permian extinction (~250 mya)

~10,000 extant species
-All aquatic
*Majority are marine
Cnidarian Characteristics
Radial symmetry around mouth


-Lack true body cavity
-Lack muscles
Lack true body cavity and lack muscles.
-Characteristic of cnidarians.
in cnidarians, the jellylike material located between the ectoderm and the endoderm
Cnidocytes (Cnidarian Taxonomy)
Five Classes:
One of five classes of cnidocytes.
-Lack medusa
-"corals", anemones
One of five classes of cnidocytes.
-Medusa stage adherent.
One of five classes of cnidocytes.
-'True' Jellies
-Reduced polyps
One of five classes of cnidocytes.
-similar to scyphozoa
-efficient swimmer
One of five classes of cnidocytes.
-both medusa and polyp
-colonial polyps observed
Cnidarian Morphology
-Absorptive, blind gut
-No true muscles
-Longitudinal arrangments of myofibrils

Blind gut: gastrovascular cavity
-May be shared by polyps
-Functional specialization, eg feeding vs reproduction

Nerve ring and/or net present in many
-Nerve net diffuse
-Ring at margin of bell
-May have greater centralization than previously interpreted
Blind Gut (Gastrovascular Cavity)
Characteristic of Cnidarian morphology.

Gastrovascular Cavity
-May be shared by polyps
-Functional specialization, eg feeding vs reproduction
Cnidocyte (contents)
-Specialized hunting cells
-Organelles: cnida(e)
Cnidarian Morphology
Endoderm -> gastroendodermis
-Digestion & absorption
-Secretory rate high
-Significant intracellular breakdown

Mesoglea - non-cellular interstitial layer
Cnidarian Morphology
Ectoderm -> epidermal layer

-Basal to body covering
-Myofibrils at the base of epidermis
-Actin+myosin fibers = "muscles"

Nerve cells
-Multi- and bi-polar
-Nerve ring integrates
-Lack cephalization/concentrated region of integration
Cnidocyte Expulsion
Osmotic pressure changes
-Calcium lost to environment
=Na+, Cl- uptake
-Water rushes in
-Cnida ejects
Cnidarian Life History
-Planula Larva
-Polyp Stage
-Medusa Stage
Planula Larva
Part of Cnidarian Life History
-Dispersal stage
-Metamorphose to polyp
Polyp Stage
Part of Cnidarian Life History
-Adhere by pedal
-Reproduce asexually, OR
-May metamorphose to, or produce medusa stage.
Medusa Stage
Part of Cnidarian Life History
-Floating stage
-Reproduce sexually
Cnidarian Sensory Reception
Broad range of modalities
-Photoreceptors (ocelli)
-Proprioceptors (Balance/gravity=statocysts)
cells that sense gravity in a cnidarian
Simple eyes on cnidarian (and other organisms) used to sense light
A unit containing statocysts for balance, ocelli for light sensitivity, and simple eyes with lenses in certain jellyfish.
Cnidarian Motility
Sessile stage
-Polyp form
-Attaches relatively strongly often with pedal
-Hydrozoa exhibit motile colonial polyps
Cnidarian Motility
Motile stages

Medusa stage
-Utilize tentacles to manipulate water flow
-Utilize velum (if present) -
---margin extends inward from bell
---produces water jet

Planula larva
-Floats with current
-Metamorphoses into polyp form generally
Cnidarian Gas Exchange
Predominantly by diffusion

Current generation by tentacles

Affected by environment
-Dissolved oxygen content
-Water temperature
-Biotic activity
Cnidarian Nutrition
Predominantly carnivorous
-Utilize tentacles
-Digested & absorbed in gastrovascular cavity

Some phagocytic activity from environment
Cnidarian Nutrition
Some are Autotrophic
-Zooxanthellae (dinoflagellates)
Cnidarian Reproduction
Can be asexual
-Pedal laceration
Cnidarian Reproduction
Can be sexual
-Typically medusa stage
-Most are dioecious
-Can be hermaphroditic
-Germ cells typically generate in gastrodermis
Having male and female reproductive organs in separate plants or animals
Cnidarian Ecosystem Services
Corals primarily

Tremendous primary producers
-Generate great secondary and tertiary diversity
-Nutrient recycling

Provide barriers for ocean

Weather modifiers
Ctenophoran Phylogeny
Arose by Devonian

Was associated with cnidarians
---Based on Ctenophora cnidae
---Cnidae actually came from diet
Bilaterally symmetrical
8 rows of cilia

Move by concerted beating of cilia
Ctenophoran Phylogeny
Separated to own phylum
-8 rows of cilia
-"comb" + "bearer"
-Aka, sea gooseberries

100-150 species
-Near shore: mm-cm
-Oceanic: up to a meter!

Many bioluminesce
Ctenophora Ecosystem Services
---Colloblast adhesive

Eaten by...
-Sea birds
Ctenophora Reproduction
Most are planktonic

Most are hermaphroditic
-Spawn into water
-Sperm find eggs
-Most self-fertile(?)

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