Micrasterias cell division

Time-lapse video of the microscopic green algae Micrasterias in the process of dividing:

"The Rotifera of the Scottish Lochs"

Illustrations of rotifers (microscopic aquatic animals) from a 1906 book. Image from Scientific Illustration.

Sand, magnified

These grains include what looks like a tiny crustacean's claw, a minuscule shell, and spines possibly from a sea urchin. Image from Nikon Small World.

Planktonic protists

The word "plankton" shares a Greek root with "planet" (πλαγκτός, meaning drifting or wandering)-- an etymological link which seems particularly appropriate for these drifting microbes, spherical or stellate in form: 

Protists - Cells in the Sea from Parafilms on Vimeo.

This beautiful clip is one of a series called Plankton Chronicles, found via The Book of Barely Imagined Beings.

Sponges and their skeletons

Images of sea sponges from the Report on the Hexactinellida collected by H.M.S. Challenger during the Years1873-76; each image shows a sponge framed by examples of the glass-like spines (called spicules) which make up its "skeleton":

Sea cucumbers also have attractive mineralized parts called spicules, but these function as external armor rather than internal support.

Dinoflagellates

These strange marine microbes are related to those which cause red tide. 

Characodictyon

This is an electron microscope image of a tiny fossil from the Precambrian era, the shell of a microbe (somewhat resembling modern radiolaria). It may be the oldest example of armor on a living creature. 

Image from Live Science. 

Micro-plants

Illustrations of algae, plants, seaweed, and fungi from Common Objects of the Microscope, by John George Wood, 1900:

Diatom mandala

This beautiful design fits on a microscope slide, and the jewel-like objects that compose it are the shells of tiny marine microbes.

Image from Klaus Kemp's diatom art site. Diatom arrangements like these, along with similar arrangements of butterfly scales, were popular in the Victorian era.

Fairy wasp

[above] The fairy wasp, Megaphragma mymaripenne... pictured next to a Paramecium and an amoeba at the same scale.
...
As they get smaller, insects can do away with many of their organs. The feather-winged beetles – twice as big as the fairy wasps, but still impressively tiny – have drastically reduced the size of their genitals, guts and breathing tubes. They have totally lost their hearts: at their size, diffusion is enough to carry liquids around their body without the need for a pump. Their wings, like those of thrips and fairy wasps, are little more than wispy strands, rather than the flat oars of most other insects. That’s all they need to paddle through thick air currents.

From Not Exactly Rocket Science.

Infusorial Animalcules

Plate from Pritchard's 'Infusorial Animalcules' 1852 showing illustrations of freshwater microscopic organisms.

Starfish larva

Image from The Echinoblog. This transparent creature grows into a many-armed sun star.

Even stranger is the starfish Luidia-- its larva splits into a juvenile starfish and a gelatinous planktonic creature, which go on to live independent lives.

Butterfly egg

 David Millard,Vanessa atalanta (Red admiral butterfly) egg in Urtica dioica (Stinging nettle) trichomes (10X)

From Nikon Small World. 

Pediastrum

A beautiful pond-dwelling microscopic algae:

Image from MicroscopyUK, which has many more photos of similar algae.

Oolite

These are microscopic sections of a sedimentary rock containing spherical grains called ooids-- which are formed of concentric layers like pearls.

"Feathers of Humming Bird, Brittle Star Fish, Fossil Tooth of Shark"

These slides have cover slips of thin glass, which was very expensive and difficult to produce before the 1840s—early mounters more often used sheets of mica, which was far from transparent. The use of Canada balsam sap (which preserves structures and eliminates air and water from samples) as a mounting medium also vastly improved the view.

From a SEED Magazine slideshow of Victorian microscope slides. Those shown above are from the collection of Howard Lynk, who has many more; the arranged slides of diatoms and spicules are quite lovely.

Foraminifera

These are the shells of marine protists, each as small as a grain of sand. They are abundant in the fossil record, showing smooth transitions from stratum to stratum.

Two sunfish

Juvenile

Skeleton of adult

Xiphostylus and Saturnalis

 

Drawings from Report on the Radiolaria collected by H.M.S. Challenger during the years 1873-76. From Scientific Illustration.

Spicules

Illustrations of spicules, spines found in the skin of sea cucumbers. 

Micro-photos of these pretty objects can be seen here and here; they also appear in the border of this sea-cucumber drawing by Ernst Haeckel.