The wallpaper on which Alexander Fleming discovered Penicillin in 1928.
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Lots of different organisms, including a two-headed platyhelminth near the end.
A little snail I found in a pond water sample. It was the size of a small pebble.
Blepharisma, a pink protist.
These microorganisms are photophobic, meaning they have an aversion to light. This makes them rather difficult to photograph since the moment you shine a microscope light on them they try to swim away.
The frustration of trying to photograph them was well worth it, though
The pictures above are of microscopic crustaceans called copepods. The first two are copepod nauplii, which are the larval forms. The third picture is an adult carrying two egg sacs.
The larvae of copepods look quite similar to the larvae of another organism…
Pictured here is a barnacle larvae. Their similar appearance is not a coincidence. Believe it or not, barnacles are also crustaceans.
Although we tend to think of crustaceans as crabs and lobsters, they actually come in a variety of forms, ranging from sessile barnacles to giant marine isopods to the blind and worm-like Remipedia. There are thousands of species that are parasites, and some are even parasites of other crustaceans.
The majority of these crustaceans are microscopic. In fact, copepods are tied with krill (also a type of crustacean) when it comes to having the highest animal biomass.
(The first three pictures are mine. The fourth picture is not mine, its from here)
Aelosoma, microscopic worms found in aquatic environments, have a unique way of reproducing. They mostly just keep growing lengthwise and then split themselves horizontally into 2 or 3 individuals. The pictures show the site of a soon-to-be split. You can see the outline of the head of the posterior worm starting to form.
How small can an animal get?
This organism is a gastrotrich, an invertebrate found in the sediment of aquatic environments. They can be as small as .06 mm, or about the size of 10 human red blood cells laid flat end to end. And keep in mind that red blood cells are smaller than most of our cells!
Despite their size, these multi-cellular animals come with their own complete digestive system, nervous system, reproductive organs, and muscle tissue. They may not be the smallest (some rotifers and obligate parasites are smaller), but they certainly push the limit for how small an animal can be.
(Photos are mine, information source is Animal Earth by Ross Piper and this)
A pair of worms under the microscope shot in dark-field.
The long, thin and somewhat yellow-ish worm is an Aelosoma, which are related to leeches and earthworms (part of the Annelid phylum). They are quite common in freshwater and are voracious feeders of algae and soil.
The smaller white worm is a turbellarian, which is a type of free-living flatworm (as opposed to parasitic flatworms, which make up around 50% of all flatworms). This species in particular was a predator, as I saw siphoning up protists and rotifers.
Although I refer to both of these two as “worms”, this does not mean they are closely related! Many life forms on earth have evolved a worm-like body. In science vernacular, we call this body shape “vermiform”. This just goes to show you that morphology alone is not enough to parse evolutionary relationships.
The first gif is mine. The protist in the gif is misidentified as an amoeba….. Anyways…