Bio Exam 4

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protists.

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Eukaryotes that are not plants, animals, or fungi have traditionally been called

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Eukaryotes are

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monophyletic.
They are thought to be more closely related to Archaea than to Bacteria.
But mitochondria and chloroplasts are clearly derived from bacterial lineages.

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Loss of cell wall

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Flexible cell surface allows infolding and increased surface area (cells can be larger).
Endocytosis is possible—pinching off bits of the environment and bringing them into the cell.

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Development of cytoskeleton:

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Simple cytoskeletons probably evolved in prokaryotes.
Greater development of microfilaments and microtubules gives support, and allows changes in shape, distribution of daughter chromosomes, and movement of materials.
Microtubules may have led to eukaryotic flagella.

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Nuclear envelope:

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Developed early in eukaryote evolution.
May have arisen from DNA attached to the membrane of an infolded vesicle.
(Prokaryote DNA is attached to the inner plasma membrane).

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Phagocytosis and digestive vacuoles

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the ability to engulf and digest other cells.

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Endosymbiosis

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: a proteobacterium was incorporated and evolved into the mitochondrion.

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What is original function of mitochondria?

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Original function of mitochondria might have been to detoxify the O2 that was being produced by cyanobacteria, reducing it to water. Later, this became coupled with formation of ATP.

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How did development of chloroplast occur?

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Development of chloroplasts occurred in a series of endosymbioses.

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Primary endosymbiosis

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a cyanobacterium was engulfed. Chloroplast has two membranes. Remnants of peptidoglycan cell wall can be found in glaucophytes.

Primary endosymbiosis also gave rise to chloroplasts of red algae, green algae, and land plants.

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Secondary endosymbiosis:

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a eukaryote engulfed a green alga cell which became a chloroplast.
Chloroplast has three membranes.

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Tertiary endosymbiosis

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a dinoflagellate lost its chloroplast and took up another protist that had acquired its chloroplast through secondary endosymbiosis.

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How many major clades of protistan eukaryotes are there?

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five
*enormous diversity
*most unicellular
*traditionally classified on the basis of life histories and reproductive features

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alveolates

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Sacs called alveoli lie just beneath plasma membrane.
All unicellular, most are photosynthetic.
Dinoflagellates
Apicomplexans
Ciliates

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Dinoflagellates:

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mostly marine; photosynthetic; important primary producers in the oceans.
Some species cause red tides.
Some are endosymbionts with invertebrates (e.g., corals).

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Apicomplexans

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obligate parasites
Apical complex—organelles at the tip of the cell; help it invade host tissue.
Elaborate life cycles featuring asexual and sexual reproduction and life stages in different hosts.
Plasmodium is the causative agent of malaria.

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Apical complex

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organelles at the tip of the cell; help it invade host tissue

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plasmodium is causative agent of what?

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malaria

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Ciliates

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numerous hairlike cilia (identical to eukaryotic flagella).
Heterotrophic; some have photosynthetic endosymbionts.

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paramecium

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is covered by a flexible pellicle with trichocysts—defensive organelles that can explode as sharp darts.

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where does paramecium live?

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Lives in fresh water: contractile vacuoles excrete excess water taken in by osmosis.
Also has digestive vacuoles

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Excavates

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Diplomonads
Parabasalids
Heteroloboseans
Euglenids
Kinetoplastids

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Diplomonads and parabasalids

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unicellular and lack mitochondria (a derived condition).

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Giardia lamblia

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causes the intestinal disease giardiasis.

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Heteroloboseans

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amoeboid body form
Naegleria has two stages, one with amoeboid cells and the other with flagellated cells.
Some species can enter the human body and cause a fatal disease of the nervous system

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Euglenids and kinetoplastids

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have flagella; mitochondria with disc-shaped cristae.
Some euglenids are always heterotrophic; some are photosynthetic but can loose their pigments and feed on organic matter.

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Kinetoplastids

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mitochondrion has a kinetoplast that contains multiple circular DNA molecules

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Trypanosomes

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are pathogens that can change cell surface recognition molecules frequently, making them hard to control.

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Stramenopiles

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Rows of tubular hairs on the longer of their two flagella
Some lack flagella but are descended from ancestors that possessed them.
Diatoms
Brown algae
Oomycetes

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Diatoms

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unicellular; some species associate in filaments
Lack flagella except in male gametes.
Deposit silicon dioxide in two-piece cell walls; intricate patterns are unique to each species.
Reproduce both sexually and asexually.
Abundant in oceans and fresh waters and are major photosynthetic producers.

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Brown algae

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brown color from the carotenoid fucoxanthin.
Multicellular, marine.

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attached forms of brown algae develop what?

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holdfasts with alginic acid to glue them to rocks. Alginic acid is used by humans as an emulsifier in ice cream, cosmetics, and other products.
Giant kelps may be up to 60 meters long

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Oomycetes

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water molds, downy mildews
Once classed as fungi

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What are all oomycetes?

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All are absorptive heterotrophs—secrete enzymes that digest large food molecules into smaller molecules that they can absorb.
Water molds—all aquatic and saprobic (feed on dead organic matter).

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Rhizaria

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Unicellular and mostly aquatic; have long, thin pseudopods.
Make up a large component of ocean sediments.
Cercozoans
Foraminiferans
Radiolarians

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Cercozoans

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soil and aquatic organisms
One group has chloroplasts derived from a green alga by secondary endosymbiosis—and that chloroplast contains a trace of the alga’s nucleus.

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Foraminiferans

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external shells of calcium carbonate
Threadlike, branched pseudopods extend through microscopic holes in the shell and form a sticky net, used to catch smaller plankton.
Accumulations of shells have produced much of the world’s limestone.

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Radiolarians

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radial symmetry; thin, stiff pseudopods reinforced by microtubules.
Pseudopods increase surface area of the cell, and help it stay afloat.
Secrete glassy endoskeletons

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Amoebozoans

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Amoeboid body form; lobe-shaped pseudopods
Loboseans
Plasmodial slime molds
Cellular slime molds

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Loboseans

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feed by phagocytosis, engulfing smaller organisms and particles with pseudopods.
Many are adapted to living on the bottoms of lakes and ponds.
Testate amoebas live in shells made from sand grains or secreted by the organism.

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Plasmodial slime molds:

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Vegetative state—plasmodium—a mass of cytoplasm with no cell walls and many diploid nuclei (a coenocyte).
Moves by cytoplasmic streaming and engulfs food particles by endocytosis

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if conditions become unfavorable for a plasmodium, it can

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form a hardened mass (sclerotium), which can re-grow into a plasmodium.
or, transform into spore-bearing fruiting structures. The haploid spores germinate to form swarm cells.
Swarm cells can live independently, form resting cysts, or fuse to form a diploid zygote which divides to form a new plasmodium.

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Cellular slime molds

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: vegetative state consists of amoeboid cells called myxamoebas.
Myxamoebas have one haploid nuclei, engulf food particles by endocytosis, and reproduce by mitosis and fission.

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If conditions become unfavorable for a cellular slime mold, they can do what?

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aggregate in a slug or pseudoplasmodium.
The slug can migrate, then form a stalked fruiting structure. Spores germinate to form new myxamoebas.

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Binary fission

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equal splitting by mitosis followed by cytokinesis

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multiple fission

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splitting of one cell into more than two cells

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budding

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outgrowth of a new cell from the surface of an old one

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sporulation

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formation of specialized cells that can develop into new individuals.

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clonal lineages

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Offspring from asexual reproduction are genetically identical to their parents

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Reproduction in Paramecium

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Two types of nuclei—one macronucleus and one to several micronuclei.
Asexual reproduction—all nuclei are copied before the cell divides.

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Conjugation

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two individuals fuse and exchange genetic material; a sexual process, but not reproductive.

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alternation of generations

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A multicellular, diploid, spore-producing organism gives rise to a multicellular, haploid, gamete-producing organism.
When two haploid gametes fuse, a diploid organism is produced.
The haploid organism, the diploid organism, or both may also reproduce asexually.

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heteromorphic

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two generations from alternation of generation differ morphologically

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isomorphic

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the two generations from alternation of generations are similar

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In the diploid organism, specialized cells called sporocytes

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divide meiotically to produce haploid spores.

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what do spores develop into?

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spores develop into the haploid organism

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what does the haploid organism from a spore produce?

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gametes by mitosis and cytokinesis that fuse to produce diploid organism

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Phytoplankton are very important what?

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primary producers, The diatoms perform about 1/5 of all carbon fixation on Earth—about the same amount as the rainforests.

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Some microbial eukaryotes are pathogens such as

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plasmodium

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Plasmodium

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*parasite in human red blood cells that causes malaria
*complex life cycle that includes mosquitoes as an alternate host
*extracellular parasite in the mosquito and an intracellular parasite in the human host

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Many microbial eukaryotes live as what?

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endosymbionts

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some photosynthetic dinoflagellates live as what?

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live as endosymbionts in corals. If the dinoflagellates die or are expelled, the coral is said to be bleached.
If the corals don’t acquire new endosymbionts, they usually die or are damaged due to reduced food supply.

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diatoms store energy as what?

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oil

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foraminiferan shells make up what?

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extensive limestone deposits, and some sandy beaches

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dinoflagellates are...?

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important component of marine ecosystems, some species produce beautiful bioluminesence in the oceans.

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All organisms

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Plasma membranes and ribosomes
Metabolic pathways (e.g., glycolysis)
Conservative DNA replication
DNA that encodes proteins
Shared features indicate that all life is related, but major differences have also evolved.

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Three domains of life

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Bacteria—prokaryotes
Archaea—prokaryotes
Eukarya—eukaryotes

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prokaryotes differ from eukaryotes

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All are unicellular
Divide by binary fission, not mitosis
DNA is often circular, not in a nucleus
No membrane-enclosed organelles

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Genetic studies show that the three domains have a what?

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single common ancestor

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before DNA sequencing, classification was based on what?

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based on phenotypic characters such as shape, color, motility, nutrition, and cell wall structure.

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what do most bacteria cell walls contain?

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peptidoglycan, antibiotics target peptidoglycan because eukaryote cells do not have it

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gram stain classification

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based on difference in cell wall structure

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gram-positive bacteria

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appear blue to purple

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gram-negative bacteria

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appear pink to red

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coccus

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sphere, occur singly or in plates, block, or clusters

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bacillus

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rod

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helix

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spiral or helix

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what two bacteria shapes would form clusters?

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rods and helical shapes

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sequencing of ribosomal RNA genes is useful for phlogenetic studies because

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rRNA was present in the common ancestor of all life.
• All free-living organisms have rRNA.
• Lateral transfer of rRNA genes among distantly related species is unlikely.
• rRNA has evolved slowly.

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Transformation, conjugation, and transduction

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allow exchange of genetic information between prokaryotes without reproduction.

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lateral gene transfer

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genes move “sideways” from one species to another. When sequenced, gene trees will not match the organismal tree.

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Genes that result in new adaptations...

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that confer higher fitness are most likely to be transferred.

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what do biologists now examine?

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Biologists now examine gene sequences collected from random samples of the environment

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Low-GC Gram-positives

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Low ratio of G-C to A-T base pairs in DNA.
Some are gram-negative, and some have no cell wall.
Some produce heat-resistant endospores that can survive unfavorable conditions. Some can survive for 1,000 years.

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Bacillus anthracis

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produces an exotoxin that causes anthrax. The endospores have been used as a bioterrorism agent.

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Staphylococcus (staphylococci

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are abundant on skin and cause boils and other skin problems. S. aureus can also cause respiratory, intestinal, and wound infections.

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Mycoplasmas

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have no cell wall, are extremely small, and have a very small genome.
They have less than half as much DNA as other prokaryotes, which may represent the minimum amount of DNA needed for a living cell.

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High-GC Gram-positives (Actinobacteria)

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Higher ratio of G-C to A-T base pairs.
Branched filaments; some form reproductive spores at filament tips.
Most antibiotics are from this group.
Mycobacterium tuberculosis causes tuberculosis; oldest know human pathogen.

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Hyperthermophilic bacteria

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Live at extreme high temperatures (extremophiles)—hot springs, volcanic vents, underground oil reservoirs.
High temperatures may have been the ancestral condition on Earth when prokaryotes evolved.
Monophyly of this group is not well established.

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Hadobacteria

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Hadobacteria
*deinococcus
*thermus aquaticus

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Deinococcus

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survive cold as well as hot temperatures and are resistant to radiation. They can consume nuclear waste

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Thermus aquaticus

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was isolated from a hot spring; source of the thermally stable DNA polymerase used in PCR.

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Cyanobacteria

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Photosynthetic; have blue-green pigments.
Many species fix nitrogen.
Chloroplasts of eukaryotes are derived from an endosymbiotic cyanobacterium.

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Cyanobacteria

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Photosynthetic; have blue-green pigments.
Many species fix nitrogen.
Chloroplasts of eukaryotes are derived from an endosymbiotic cyanobacterium.

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Spirochetes

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Gram-negative; motile
Unique axial filaments (modified flagella) that rotate
Many are human parasites, some are pathogens (syphilis, Lyme disease), others are free living.

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Chlamydias

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Can live only as parasites in cells of other organisms.
Gram-negative; extremely small
Can take up ATP from host cell with translocase
Complex life cycle with two forms—elementary bodies and reticulate bodies

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Proteobacteria

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largest group of bacteria
Mitochondria of eukaryotes were derived from a proteobacterium by endosymbiosis.
Some are photoautotrophs that use light energy to metabolize sulfur; some are N-fixers (Rhizobium).
Escherichia coli is one of the most studied organisms on Earth.

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Agrobacterium tumefaciens-proteobacteria

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causes crown gall disease of plants and has a plasmid used in recombinant DNA studies.

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what do many proteobacteria include?

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include many pathogens— cholera, bubonic plague, salmonella.

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what is the separation of the archaea domain from bacteria domain based on?

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genome sequencing

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two main groups of archaea

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*euryarcheota
*crenarcheota

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What is common to all archaea?

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*all lack peptidoglycan
*have unique lipids in the cell membranes

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Bacterial and eukaryotic membranes have lipids with fatty acids connected to glycerol by?

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ester linkages

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archael membranes have lipids with fatty acids linked to glycerol by?

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ether linkages

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What is the similarity of the linkages?

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synapomorphy of archaea

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Some Euryarcheota are methanogens

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CH4 is produced by reducing CO2; they are obligate anaerobes.
Methanogens release 2 billion tons of methane per year. Many live in the guts of grazing mammals, termites, and cockroaches.
Increased cattle farming and rice growing contributes methane to the atmosphere.

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Extreme halophiles

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have pink carotenoid pigments.
Live in the most salty, most alkaline environments on Earth.
Some have a light-absorbing molecule, microbial rhodopsin, to trap light energy and form ATP.

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Biofilms—

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cells bind to a solid surface and secrete a sticky polysaccharide matrix that traps other cells

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why are cells in biofilms hard to kill?

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Can form on any surface, including contact lenses, artificial joint replacements, metal pipes.
Dental plaque are biofilms on our teeth.

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Anaerobes

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do not use oxygen as an electron acceptor in respiration.

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Obligate anaerobes

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oxygen is poisonous

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Aerotolerant anaerobes

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not damaged by oxygen

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facultative anaerobe

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use both aerobic and anaerobic metabolic pathways

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obligate aerobes

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require oxygen

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Photoautotrophs

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perform photosynthesis; use CO2 as carbon source.
Cyanobacteria use chlorophyll a and produce O2.

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Photo autotrophs that use bacteriochlorophyll

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and produce sulfur; H2S is the electron donor.

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Bacteriochlorophyll

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absorbs longer wavelengths than chlorophyll.
Bacteria using this pigment can grow in deeper water under dense layers of algae, using light that is not absorbed by the algae.

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Photoheterotrophs

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use light as an energy source, but get carbon from organic compounds made by other organisms.
Sunlight provides the ATP through photophosphorylation.

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Chemolithotrophs (chemoautotrophs)

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get energy by oxidizing inorganic substances and use it to fix carbon.
Inorganic compounds oxidized include ammonia, nitrite, hydrogen gas, hydrogen sulfide, sulfur, and other materials.

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Chemoheterotrophs

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get both energy and carbon from organic compounds that have been synthesized by other organisms.
Most known bacteria and archaea are chemoheterotrophs—as are all animals, fungi, and many protists.

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Prokaryotes-decomposers

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: they metabolize organic compounds in dead organic material. The inorganic products, such as CO2, are returned to the environment.
Other prokaryotes oxidize inorganic compounds and also play key roles in element cycling.

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Denitrifiers

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Bacteria that use nitrate (NO3–) as an electron acceptor in place of O2 in anaerobic conditions.
They release N2 to the atmosphere.
They play a key role in nitrogen cycling.

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Nitrogen fixers

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Convert N2 to ammonia. Ammonia is a form of nitrogen that is useable by organisms.
Nitrogen fixation is vital to life and is done only by certain prokaryote species.

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Nitrifiers:

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Chemolithotrophic bacteria that oxidize ammonia to nitrate.
Nitrate is the form of nitrogen most easily used by many plants.

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Koch’s postulates

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were rules for establishing that a particular microorganism causes a particular disease.

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Consequences of bacterial infections depend on

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invasiveness of the pathogen (ability to multiply in host’s body) and its toxigenicity (ability to produce toxins).

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consequences of bacterial infections depend on...

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invasiveness of the pathogen (ability to multiply in host’s body) and its toxigenicity (ability to produce toxins).

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Endotoxins

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are released when certain Gram-negative bacteria lyse (burst); rarely fatal; they cause fever, vomiting, and diarrhea.

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Exotoxins

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are released by living bacteria; highly toxic, often fatal.

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Exotoxins

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are released by living bacteria; highly toxic, often fatal.

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Negative-sense single-stranded RNA viruses:

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Negative-sense RNA—the complement of mRNA.
Specialized RNA polymerase ton make mRNA from their negative-sense RNA genome.
These viruses probably arose by cellular escape many times independently across the tree of life.
Includes viruses that cause measles, mumps, rabies, and influenza.

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Positive-sense single-stranded RNA viruses:

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Already set for translation, no replication of compliment strand is necessary
The most abundant and diverse group; includes mosaic viruses of crop plants, polio, hepatitis C, and the common cold.
They also appear to have evolved multiple times across the tree of life from different groups of cellular ancestors.

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RNA retroviruses

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Single-stranded RNA; probably evolved as escaped cellular components.
Regenerate themselves by reverse transcription. DNA is produced and integrated into the host genome, where it is replicated along with host’s DNA.
Only infect vertebrates; includes HIV, and some are associated with various cancers.

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Double-stranded RNA viruses:

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May have evolved repeatedly from single-stranded RNA ancestors.
Cause many plant diseases and infant diarrhea in humans.

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Double-stranded DNA viruses

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May represent highly reduced parasitic organisms that have lost their cellular structure and ability to survive as free-living species.
Some have genomes as large as parasitic bacteria.
Includes bacteriophage, smallpox, and herpes viruses.

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Red algae

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multicellular; have phycoerythrin and other pigments.
Most are marine and the ratio of phycoerythrin to chlorophyll a depends on light intensity or water depth.
> phycoerythrin deeper water
> chlorophyll a shallow water

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three clades of green algae

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Chlorophytes
Coleochaetophytes
Charophytes

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key synapomorphy of land plants

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an embryo that is protected by tissues of the parent plant.

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key synapomorphy of the land plants

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an embryo that is protected by tissues of the parent plant. They are also called embryophytes

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Vascular plants (tracheophytes

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well developed vascular systems with tracheids

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Non-vascular plants

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some have conduction cells, but no tracheids. Not a clade.

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Sporophyte

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the multicellular diploid plant
Cells in the sporangia produce haploid spores by meiosis.
Spores develop into the gametophyte, the multicellular haploid plant.
Gametophyte produces haploid gametes by mitosis.
Fusion of gametes produces a diploid zygote, which developed into the sporophyte

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Liverworts

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Green, leaflike gametophytes
Sporophyte remains attached to the larger gametophyte.

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Mosses

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Have stomata
Have cells called hydroids, which die and leave a channel through which water can move.

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Hornworts

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Sporophytes look like small horns.
Cells contain one chloroplast.
Have a symbiotic relationships with cyanobacteria that live in internal cavities and fix nitrogen.

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tracheid

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evolved in sporophytes and was critical for evolution of land plants.
Tracheids allow transport of water and materials.
Lignin in the cell walls provides structural support, allowing taller growth.

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vascular system consists of

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tissues specialized for transport of water and materials from one part of the plant to another.

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evolution of vascular tissue allow what?

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land plants to spread to new environments and diversify rapidly.

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Evolution of vascular tissue

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allowed land plants to spread to new environments and diversify rapidly.

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Colonization of land by vascular plants made the terrestrial environment more what?

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more hospitable to animals

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Rhyniophytes

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earliest vascular plants
No roots; were anchored in soil by rhizomes (like ferns today)
Dichotomous branching pattern

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Lycophytes

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club mosses
True branching roots
Have leaflike structures (microphylls), arranged spirally on the stem
Dichotomous branching
Sporangia in club-like clusters called strobili

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Monilophytes

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horsetails and ferns: a clade
A synapomorphy: leaf gaps in stem where leaves emerge.
Also have differentiation between main stem and side branches

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Horsetails

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all in genus Equisetum
Reduced true leaves in whorls
True roots
Independent sporophyte and gametophyte
Only about 15 species remain living all in the genus Equisetum

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Leptosporangiate ferns:

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Sporangia walls only one cell thick
Most are terrestrial; a few aquatic species
Require liquid water for movement of sperm, so most inhabit moist woodlands and swamps
Gametophyte is small and short-lived; sporophyte can be very large and can sometimes survive for hundreds of years.
Sporangia are borne on a stalk in clusters called sori, on the undersurfaces of the leaves

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Euphyllophytes

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clade consisting of monilophytes and seed plants

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Overtopping growth

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one branch differentiates from and grows beyond the others; an advantage in competition for light.

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Megaphylls

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more complex leaf; may have arisen from flattening of a branch tip.

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heterosporous

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most vascular plants

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heterosporous-megaspore

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develops into a female gametophyte (megagametophyte) that produces only eggs.

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heterosporous-microspores

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develop into a male gametophytes (microgametophytes) that produce only sperm.

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Seed plants (gymnosperms and angiosperms

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Seeds provide a secure and lasting dormant stage for the embryo.
Seeds can be dormant for many years, even centuries.

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Secondary growth

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growth—increasing diameter of roots and stems by growth of xylem—forms wood.
Older wood becomes clogged with resins but provides support and allows plants to grow to great heights.
Many plant groups have lost the woody growth habit.

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Gymnosperms

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seed plants that do not form flowers or fruits.
Ovules and seeds are not protected by ovary or fruit tissue.
Have only tracheids as the water-conducting and support cells within the xylem.

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four groups of gymnosperms

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cycads
gingkos
gnetophytes
conifers

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Cycads

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tropical, earliest diverging clade

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Gingkos

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common in Mesozoic, today only one species: Gingko biloba

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Gnetophytes

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some characteristics similar to angiosperms; Welwitschia

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Conifers

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cone-bearing plants

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Cones of conifers: two types

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Megastrobilus—female cone, seeds protected by woody scales
Microstrobilus—male pollen-bearing cone

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Inflorescence

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group of flowers; types are characteristic of plant families.

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Petals (collectively, the corolla) and sepals

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(collectively, the calyx) can be important in attracting pollinators

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General characteristics of animals:

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• Multicellularity
• Heterotrophy
• Internal digestion
• Motility
But these are not diagnostic for all animals.

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What was the common ancestor to all animals?

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probably a colonial flagellated protist;
Similar to existing colonial choanoflagellates and sponges.
Cells in the colony began to specialize for different functions.
Coordination among groups of cells may have been improved by regulatory molecules; eventually leading to larger, more complex animals.

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Diploblastic-developmental patterns

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animals have 2 cell layers—ectoderm and endoderm

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triploblastic- developmental patterns

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have 3 cell layers—ecto-, endo-, and mesoderm

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Gastrulation

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hollow ball of cells indents and forms a cavity, the blastopore.

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Protostomes

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blastopore develops into the mouth.

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Deuterostomes

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blastopore develops into the anus; mouth develops later.

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Body plan

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general structure, arrangement of organ systems, and integrated functioning of body parts.

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Four key features of body parts?

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• Symmetry
• Body cavity structure
• Segmentation
• External appendages

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Symmetry

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is overall shape.

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radial symmetry

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body parts arranged around a central axis.

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Bilateral symmetry

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can be divided into mirror image halves on only one plane.

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what is bilateral symmetry associated with?

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cephalization—concentration of sensory organs and nerve tissues at the anterior end, or head.

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Segmentation

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facilitates specialization of body regions.
Also allows animal to alter body shape and control movements precisely.
Radiation of the arthropods was based on changes in a segmented body plan.

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what do appendages enhance?

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animal’s ability to move around to find food, avoid predators, and find mates.

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what do limbs allow for?

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for highly controlled, rapid movement. Arthropods and vertebrates have jointed limbs. In some groups they are modified into wings.

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Bilateria

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monophyletic group that includes protostomes and deuterostomes.
• Bilateral symmetry
• Triploblastic
• At least 7 Hox genes

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Eumetazoans:

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• Body symmetry
• A gut, and nervous system
• Tissues organized into distinct organs
Includes all animal groups except sponges and placozoans.

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Sponges

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no distinct tissue types
Have hard skeletal elements called spicules
Glass sponges and demosponges—spicules made of silicon dioxide
Calcareous sponges—spicules made of calcium carbonate

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Sponge body plan

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aggregation of cells around a water canal system.
Water and food particles enter through small pores and pass into the canal system where the choanocytes capture food particles.
Water movement results from the beating of the choanocyte flagella.

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Placozoans:

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• Four cell types; weakly differentiated tissue layers
• Flattened animals that adhere to substrates; asymmetric
• Diploblastic
• Have a swimming, pelagic stage
Some features of the very simple body plan may be secondarily derived.

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Ctenophores (comb jellies):

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• Radial symmetry;
• Diploblastic; gelatinous extracellular matrix called mesoglea between the layers
• Move by beating cilia arranged on 8 comb-like plates called ctenes
• Complete gut; feed with tentacles that discharge sticky material to trap plankton

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Cnidarians:

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• Jellyfishes, sea anemones, corals, hydrozoans
• Nearly all are marine
• Radial symmetry

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• Gastrovascular cavity of cnidarians

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functions in digestion, circulation, and gas exchange, and as a hydrostatic skeleton
• Life cycle with sessile polyp and motile medusa stages