As usual, Naturally Curious readers submitted unbelievably creative ideas about the identity of yesterday’s Mystery Photo. Kudos to those of you who recognized that it was a slime mold. Slime molds look like a fungus, and reproduce with spores like fungi do, but are no longer classified as fungi. Slime molds are made up of individual organisms that form a mass called plasmodium. They can be bright orange, red, yellow, brown, black, blue, or white. These large masses act like giant amoebas, creeping slowly along and engulfing food particles (decaying vegetation, bacteria, fungi, and even other slime molds) along the way. If a slime mold is cut up into pieces, the pieces will pull themselves back together.
The most common species are in a group called plasmodial slime molds. They share one big cell wall that surrounds thousands of nuclei. Proteins called microfilaments act like tiny muscles that enable the mass to crawl at rates of about 1/25th of an inch per hour. A slime mold mass can actually navigate and avoid obstacles. If a food source is placed nearby, it seems to sense it and head unerringly for it.
As long as conditions are good, (enough food and moisture and favorable pH), the mass thrives. But when food and water are scarce, the mass transforms itself into spore-bearing fruiting structures. These typically form stalks topped by sphere-like fruiting bodies called sporangia that contain spores that are carried by the rain or wind to new locations. After they have been dispersed, each of these spores will germinate and release a tiny amoeba-like organism which, if it successfully finds and fuses with another similar organism, can then begin to feed and develop into a new plasmodium.
The pictured slime mold, Coral Slime (Ceratiomyxa fruticulosa), is one of the more common slime molds. It is unusual in that it produces its spores externally on small stalks, not in sporangia, which gives it a fuzzy appearance.
To watch a time-lapse video of slime mold moving, go to https://www.youtube.com/watch?v=GY_uMH8Xpy0.
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