Slime Molds

Friday, July 9, 2010

These three organisms presented are true slime molds, or myxogastrias (formerly called myxomycetes). Myxogastrias (differing from dictyostelids—other slime molds) are fascinating creatures displaying some characteristics of a fungus and some of an animal. Originally grouped as a fungus, they are now classified as a fungus-like protist in the domain Eukarya, with some uncertainty.

The basic life cycle of a myxogastria is roughly this: Spores, produced by the fruiting bodies, wait for favorable conditions to germinate, generally on decaying organic matter. The spores release between one and four unwalled haploid cells, which are either amoeboid or flagellated as their mode of movement. In free water areas, flaggelated cells tend to be predominant. The haploid cells feed and grow, dividing individually and creating more haploid cells. In the event of unfavorable conditions at this stage, the cell can become a dormant structure called a microcyst. These can remain viable for extended periods of time underground, and reemerge when the conditions are better.

At length, two haploid cells will mate, combining their nuclei and cells to form one diploid cell, or zygote. This begins the period that earns the common name “slime mold.” As the diploid cell feeds and grows, it begins a set of nuclear divisions. However, since only the nuclei divide, and not the cell (although it continues to grow), the slime mold becomes a multinucleate “macrocell,” containing hundreds or thousands of individual nuclei. This is called the plasmodium. During this phase of the myxogastria’s life cycle, it is visible as a slimy growth, often brightly colored, that moves very slowly as it feeds and searches for a good place to fruit. It is this life stage, too, that created some of the first panic of an alien invasion: imagine a slimy mass in your backyard that can be feet across and is in a slightly different place every time you look out the window! At some point, the plasmodium is mature and transforms into the fruiting bodies, which can be dramatically different depending on the species, and release spores into the air and begin the cycle again.

Some mention should be made of the other group of slime molds: the dictyostelids, which occupy a different class within the phylum Mycetozoa. The dictostelids appear similar to the myxogastrias, but are actually quite different. Instead of one macrocell forming the plasmodium, many free-living unicellular organisms will aggregate and form the plasmodium, and then the fruiting bodies. Their reason for and method of cooperation are unknown; also, the organisms that become the fruiting bodies and the organisms that become, say, the stalks will obviously have dramatically different input in the genes present in the spores. That apparatus is also a mystery.

All specimens were collected by Becky near Pond Drain. Articles with help from Mary Jane.

Articles by Hazel Galloway

Eyelash Cup Fungi
Scutellinia scutellata

This fungus is unique among the organisms displayed here because it is, in fact, a fungus. This eyelash cup is so named because of the small hairs present around the outside of the cup, resembling eyelashes. Actually, the entire sterile (lower) surface of the fungi is covered in tiny hairs, but the ones on the edge of the fertile (upper) surface, the “cup,” are most prominent. In general, this fungus has a pale brown sterile surface covered with small hairs, and a distinctive, red-orange fertile surface, from which it produces the ascospores. It can be 0.2-1 cm in diameter, and does not have a stalk. The young fungi begin nearly spherical, but as they mature they open up into flat discs.

S. scutellata can be found on almost every continent in the world, although it is most common in Europe and North America. It is a saprophyte and typically lives on rotting wood or other organic debris. In North America, it generally fruits in the spring. Though, as in this case, they sometimes fruit alone, it is more common to find them fruiting in groups on a single piece of rotting wood. It is not classified as inedible, but it has no known nutritional value.

See images of the Eyelash Cup Fungus here, courtesy of

Stemonitis sp.
This myxogastria is of the genus stemonitis, which can be found in most parts of the world. The fruiting bodies here are a typical sporangia formation with a brown, spore-producing head. The feathery appearance is misleading; the sporangium resemble, under magnification, smooth stalks. The plasmodium of this species is composed of a network of fine, transparent strands. It lives generally on rotten wood, and fruits in May through October.
See images of the stemonitis here, courtesy of Messiah College.
Hemitrichia (calyculata?)
This is another myxogastria. Its fruiting body is easily identified by the yellow “puffball” shape emerging from the peridium. It can be found from .15 to .3 cm tall. It has the same life cycle as the stemonitis above, and also tends to live on rotten pieces of wood. It can be found throughout most of the world, but is more common in tropical zones.

See images of Hemitrichia calyculata (if Hemitrichia calyculata it is) here, courtesy of the Encylopedia of Arkansas History and Culture.


Unknown myxogastria
Our last myxogastria is unidentified. It can be expected, however, to lead a reasonably similar life as the previous two, especially because of the similar habitat which it inhabits.