Taxonomic group: Desmid

Scientific name: Micrasterias incisa

A large single‑celled desmid, 200–300 microns in diameter, formed by two semicells that create striking bilateral symmetry. At the centre lies the round isthmus, housing the nucleus and serving as the growth zone for new cell wall material. Its bright green colour comes from a pair of large chloroplasts - one in each semicell - each lined with pyrenoids, visible as darker dots that boost carbon fixation. The long, slender arms form an elegant mirror‑image shape, making this genus a key model for understanding how plant cells generate complex forms and symmetry.

These desmids thrive in slightly acidic freshwater habitats and contribute significantly to primary production, often serving as indicators of clean, stable aquatic environments.

Location found: Shallow dam, Eltham NSW

Microscopy technique: Polarised light. 100x magnification. 

Under polarised light desmids glows with vivid colours due to birefringence, a property of its cellulose‑rich cell wall, where crystalline layers split light into different wavelengths and reveal hidden structural detail.

Taxonomic group: Chlorophyta

Scientific name: Volvox 

Large spherical colonies, ~500 microns in diameter, each composed of hundreds to thousands of cells embedded in a clear, gelatinous matrix made of extracellular polysaccharides. The smaller outer cells that dot the spheres surface are called somatic cells, each have a pair of flagella, and together they beat in coordinated waves that allow the entire colony to roll toward light for photosynthesis. Inside the sphere sit larger reproductive cells, or gonidia, which divide to form daughter colonies that eventually break free from the sphere. This clear division between somatic and reproductive roles makes Volvox a key evolutionary model for understanding early multicellularity and the emergence of cellular cooperation, offering a living window into the early evolution of complex life.

Volvox thrives in warm, calm freshwater and often blooms after periods of strong sunlight or mild nutrient enrichment. It forms an important food source for zooplankton such as rotifers and small crustaceans, linking microscopic primary producers to higher trophic levels.

See fottage of Volvox down the microscope here.

Location found: Shallow dam, Eltham NSW

Microscopy technique: Dark field illumination. 100x magnification

Taxonomic group: Desmid

Scientific name: Closterium kuetzingii

A single crescent‑shaped cell, ~ 300 microns in length, with a long, slender midregion built around a central axial line from which the two chloroplasts sit symmetrically. These chloroplasts run along the cells midsection and contain dark green pyrenoids that enhance carbon fixation during photosynthesis. The smoothly tapered tips are colourless extensions of the rigid cellulose cell wall, forming elongated, beak‑like ends that contrast with the greener central body. Just beyond each chloroplast lie tiny crystalline inclusions, likely calcium‑based, thought to assist with mineral balance and subtle orientation control. The elongated, curved form is an adaptation for life suspended in the water column, improving nutrient uptake, buoyancy, and light exposure.

Found in soft, slightly acidic, low‑nutrient fresh water that supports diverse desmid communities.

Location found: Shallow creek, Pearces Creek NSW

Microscopy technique: Bright field illumination. 400x magnification.

Taxonomic group: Desmid

Scientific name: Micrasterias

This Micrasterias cell is captured in the final stages of division, revealing the genus’s distinctive pattern of growth from the centre outward. The two newly formed semicells are nearly complete but noticeably smaller and less elaborate than the mature pair, a hallmark of desmid division. Each new semicell contains a developing chloroplast that has not yet expanded to fill the full lobed structure, leaving the younger halves paler and less densely patterned.

Division in Micrasterias begins at the central isthmus, where the nucleus sits and new wall material is secreted. From this midpoint, each daughter semicell grows outward, gradually sculpting the intricate lobes and arms characteristic of the species. Once fully formed, the cell will separate cleanly at the central junction, producing two genetically identical individuals that will repeat the process.

Location found: Booyong Nature Reserve NSW

Microscopy technique: Dark field illumination. 100x magnification.

Taxonomic group: Desmid

Scientific name: Micrasterias

This Micrasterias cell has recently separated after division, shown by the unequal size of its two semicells. The older semicell is fully developed, while the new one is still expanding outward from the central isthmus, where all growth begins during cell division. In both halves, bright green chloroplasts fill the intricate lobes, with the younger semicell’s chloroplast continuing to spread into the newly formed spaces as the semicell grows.

Under polarised light, the cell wall glows with vivid colours due to birefringence in its crystalline cellulose layers. Bright twinkling points appear across the cell under polarised light - these are tiny crystalline inorganic mineral deposits that refract polarised light, casuing them to shine and glow.

Micrasterias thrives in soft, slightly acidic, low‑nutrient freshwater and is widely used as an indicator of clean, stable aquatic environments. 

Location: Still puddle, Minyon Falls NSW

Microscopy technique: Polarised light. 100x magnification.

Taxonomic groups: Filamentous & Diatom

Two pennate diatoms appear here (right) in the final stage of asexual division, still joined together as their newly formed silica halves harden. Their elongated frustules are lined with fine striae, and inside, brown fucoxanthin‑rich chloroplasts sit alongside large refractive oil droplets that store energy and help regulate buoyancy - a feature that also underpins their value in algal biofuel research.

Beside them lies a fragment of Spirogyra, a long filamentous green alga. Its spiral chloroplasts are clearly visible, each dotted with rounded pyrenoids, specialised centres for carbon fixation and starch formation during photosynthesis. 

Pennate diatoms thrive on sediments, aquatic plants, and biofilms in clean, slightly acidic to neutral freshwater, where their sensitivity to pollution makes them reliable indicators of water quality. Spirogyra forms floating mats in calm water and strong anchored colonies in fast flowing waters.

Location: Freshwater lake, Skennars Head NSW

Microscopy technique: Bright field illumination. 400x magnification.

Taxonomic group: Diatom

This diatom is a microscopic alga enclosed in a silica frustule (shell), its long shape marked by distinct grooved vertical striae. The brown colouration is the chloroplast, and dense oil droplets are also clearly visible inside the cell - a trait that has drawn interest for biofuel research. It moves by gliding, secreting a thin film of mucus through a central raphe slit, the deep groove that runs the length of the cell, that lets them slide across surfaces. The chloroplast performs photosynthesis to produce sugars however the alga can switch to the stored oil reserves when light is limited. 

Over millions of years, the accumulated frustules of ancient diatoms have formed vast deposits known as diatomaceous earth.

These diatoms inhabit freshwater and marine environments, from streams and ponds to sediments and damp soils. They form a major base of aquatic food webs and are eaten by zooplankton, small crustaceans, filter‑feeding invertebrates, and larval fish. Their gliding ability allows them to colonise rocks, plants, and sediments, where they play a key role in primary production.

Location: Evans Head NSW

Microscopy: Bring field illumination. 400x magnification.

Taxonomic group: Chlorophyta

Names: Volvox, commonly called Globe Algae.

This close‑up of a Volvox colony reveals its elegant spherical structure, formed by hundreds of tiny somatic cells arranged on the surface and connected by thin strands of cytoplasm that allow the colony to coordinate its movement. Inside the sphere sit the larger reproductive cells, or gonidia,. which divide to form daughter colonies that eventually mature and break free from the sphere.

Each somatic cell carries a pair of flagella that beat in synchrony, propelling the entire colony through the water in a smooth rolling motion. The reproductive cells specialise in growth and division, while the somatic cells handle movement and protection - a simple but striking example of early cellular differentiation in multicellular life.

Volvox thrives in freshwater ponds, lakes, and quiet backwaters, where sunlight is abundant for photosynthesis. They form an important part of planktonic communities and are grazed upon by small crustaceans, rotifers, and filter‑feeding insects. Their cooperative structure and division of labour make them a key organism in studies of multicellularity and evolutionary transitions.

Location: Eltham NSW

Microscopy: Dark field illumination. 400x magnification.

Taxonomic group: Desmid

Scientific name: Cosmarium sp.

This image shows a colony of exceptionally small Cosmarium desmids, each cell made of two nearly hexagonal semicells joined at a narrow central isthmus. Inside each semicell sits a distinct round chloroplast and several cells have been caught in the act of division, with new semicell material forming from the central axis. This is the characteristic way desmids grow and divide, producing a fresh semicell on each side before separating.

Threaded among the colony are streaks of rod‑shaped bacteria that commonly share the same diverse biofilm habitats as many microalgae. 

Location: Minyon Falls NSW

Microscopy: Bright field illumination. 400x magnification.

Taxonomic group: Blue-green algae (cyanobacteria)

This image shows a tightly coiled colony of rounded blue‑green algae cells joined end‑to‑end. The cells divide in sequence to maintain the continuous filament. Blue‑green algae also known as cyanobacteria, are ancient photosynthetic organisms that evolved more than 2.5 billion years ago and invented the process of photosynthesis, which was responsible for the Great Oxidation Event, the moment Earth’s atmosphere first filled with oxygen. 

Their invention of chlorophyll‑based photosynthesis later became the foundation for all plant and algal lineages through a process called endosymbiosis - where a primitive cell engulfed a cyanobacteria and turned it into a chloroplast, enabling it to photosynthesise. This occurence has since shaped every ecosystem on earth.

Their spiral shape helps them stay suspended where light is strongest. They are grazed by zooplankton, filter‑feeding invertebrates, and larval fish throughout various fresh, brackish and marine habitats. 

Location: Eltham NSW

Microscopy: Bright field illumination. 100x magnification.

Taxonomic group: Filamentous algae

Names: Spyrogyra, commonly called water silk

These strands of Spirogyra show the classic spiralling chloroplast bands that wrap through each elongated cell in smooth helical ribbons. These large chloroplasts make it an efficient photosynthesiser. The filament is made of many cells joined end‑to‑end, separated by clear septums that mark each cell boundary. In the centre of every cell sits a faint, rounded nucleus, held in place by delicate cytoplasmic strands that radiate outward like fine arms. The nucleus is the cell’s control centre, housing the DNA that directs growth, metabolism, reproduction and maintains the spiralling structure of the chloroplasts.

Spyrogyra thrives in various water environments rich in sunlight and nutrients. I can form floating mats on the surface of still water or form thick colonies in running water.

Location: Angourie NSW

Microscopy: Bright field illumination. 400x magnification.