General Characteristics

• Cell wall
• Many also have a capsule
• No organelles
• Very small
• Circular DNA
• Reproduce by simple binary fission

Heterotrophic Bacteria

• Detritivores
• Important in the detrital food chain
• Recycle nutrients
• Some are denitrifying

Autotrophic Bacteria

• Some are photosynthetic
• Some are chemosynthetic (H₂S, CH₄)

Cyanobacteria (Blue-Green Algae)

• Contain chlorophyll and phycocyanin
• Have thylakoid-like membranes
• Reproduce by division
• Tolerate wide ranges of salinity & temperature
• Some are nitrogen fixers

Occurrence & Distribution of Cyanobacteria

• Form mats and crusts at high tide
• Epiphytic & epizootic
• Symbiotic with fungi in lichens
• Endoliths (burrow in calcareous rocks & coral skeletons)

Which Kingdom?

• Traditionally algae have been placed in Plantae.
• Other systems have placed some in Plantae and other groups in Protista.
• Still others have put all the algae in Protista.
• Some still keep all the algae in Plantae (All have chlorophyll a).

General Characteristics

• Carotenes and xanthophylls more abundant in chloroplasts.
• Excess photosynthetate stored chrysolaminarin & oil.
• Cell walls silicified in some.
• 325 genera, 6000 species.

3 Classes

1. Xanthophycae (yellow-green algae) 80 genera, 450 species. Mostly freshwater.
2. Chrysophyceae (golden-brown algae) 70 genera, 325 species. Fresh and saltwater.
3. Bacillariophyceae (diatoms) 200 genera, 5000 species. Everywhere.

General Characteristics

• many planktonic, some epiphytic and benthic.
• May be unicellular, colonial or filamentous.
• Two cell shapes in unicellular forms: pennate and centric.

Structure of Frustule

• Composed of two valves: epitheca and hypotheca, 1st larger.
• Usually attached to each other by girdle bands.
• A prominent band called the raphe transverses each valve.

Asexual Reproduction

• Nuclear division and cytokinesis result in a frustule containing two protoplasts.
• As the protoplasts enlarge they each use one valve as their new epitheca.
• One new cell therefore smaller than other.
• There appears to be the ability in some to enlarge the girdle band and valve slightly.
• Others are able to extrude all or part of the protoplast and form a new and larger frustule.

Sexual Reproduction (pennate diatoms)

• 2 cells pair and 2 isogametes produced by each.
• Gametes fuse to form auxospores (zygotes) which increase in size, elongate and secrete new valves.

Sexual Reproduction (centric diatoms)

• Similar to pennate diatoms but oogamous.
• Vegetative cell that becomes the oogonium goes through meiosis and only one egg survives.
• Sperm swim to oogonium and fertilize the egg which is then an auxospore.

General Characteristics

• Often classified as protozoa by many protozoologists.
• Includes chlorophyllous and colorless organisms.
• Carotenoid pigments so abundant that chl a and b are masked.
• Accumulate starch in chloroplasts and cytoplasm.
• Motile cells have 2 flagella.
• 1 is long and extends posteriorly to direction of motion.
• 2nd is ribbon like and lies in a transverse groove in which it undulates.
• Nucleus very interesting.
• DNA remains condensed all the time.
• No RNA or histones.
• Sometimes referred to as Mesokaryotes.

Ecological Importance

• Some cause red tides (Noctiluca, Ceratium & Gonyaulax)
• Some live in other plants (zoochlorellae) or animals (zooxanthellae)
• Bioluminescence present in some (Noctiluca, Pyrodinium & Gonyaulax)

Reproduction

• Asexual reproduction occurs by simple cell division usually in motile cells.
• Sexual reproduction.
• Small individuals in Ceratium may function as gametes.
• Female gamete often similar in size to vegetative cell.

Note on reproduction: Many reproduce asexually, some by syngamy.

I. Phylum Foraminifera

• Have a CaCO₃ test which is microscopic and several chambered
• Retractable pseudopodia for trapping food
• Most are benthic (attached or unattached)
• Some are abundant & planktonic
• Dead tests for foraminiferan ooze (White Cliffs of Dover)
• Most species are microfossils (useful in climate studies and oil)

II. Phylum Polycystina or Actinopoda (Radiolarians)

III. Phylum Ciliophora (Ciliates)

• Possess tiny cilia for locomotion & feeding
• Benthic, epiphytic, epizootic & endozootic (intestines of sea urchins)

Characteristics

• Multicellular
• Some are detritivores
• Some are parasitic
• Some are symbiotic with blue-green algae (lichens)

Reproduction

More Sites to Visit

• Introduction to the Bacillariophyta
• Marine Diatom Photos from Centex
• Dinoflagellates
• Dinoflagellates: Swimming phytoplankton

Back to the BIOL 331 Syllabus