Anatomy of a Slime Mold
Estimated Time: 10–15 minutes
Course: Myxomycetes 101 — Introduction to Slime Molds
Lesson Type: Reading + Media (self-paced)
1. From Blob to Architecture
When a slime mold completes its journey as a plasmodium, it performs one of the most extraordinary feats in the microbial world — it builds a structure.
The fruiting body, or sporocarp, is a miniature masterpiece of biological engineering.
Each component has a precise role in spore protection, maturation, and dispersal.
Fruiting bodies of myxomycetes range from less than a millimeter to several millimeters tall, each with complex internal architecture.
2. Overview of the Fruiting Body
Though there’s tremendous diversity among genera, most myxomycete fruiting bodies share a similar blueprint.
Picture a tiny sporangium — a capsule perched on a stalk, filled with a network of threads and spores.
Common Components
Peridium – the outer wall
Capillitium – the internal thread network
Columella – central pillar (when present)
Hypothallus – the base or “foot”
Stalk – the supporting column
Spores – the reproductive units
Parts of a myxomycete sporocarp
3. The Peridium — Protective Skin
The peridium is the outer shell or wall of the fruiting body.
It protects the developing spores and internal structures from desiccation, UV light, and microbial attack.
Key Features:
Often single-layered and membranous, sometimes covered with lime crystals. Can be double or triple layered.
Can be papery, iridescent, or brittle, depending on the species.
Splits open or disintegrates when spores mature, aiding release.
Fruiting bodies of myxomycetes range from less than a millimeter to several millimeters tall, each with complex internal architecture.
Fun Fact:
The color and texture of the peridium are often diagnostic features used in myxomycete identification.
4. The Capillitium — The Dispersal Network
Inside the sporangium, a network of delicate threads called the capillitium weaves between the spores.
These threads act like springs or levers, responding to humidity and air currents to help release spores gradually.
️ Function in Dispersal:
As humidity changes, capillitial threads expand and contract, shaking spores loose.
Prevents all spores from releasing at once — maximizing dispersal opportunities.
Variations:
In Trichia and Hemitrichia, the threads are ornamented or spiraled.
In Arcyria, they are elastic and free.
Some genera (e.g., Licea) lack a true capillitium altogether.
The elastic threads of the capillitium move in response to humidity, releasing spores in bursts.
5. The Columella — The Central Pillar
The columella is a central core or column that rises from the stalk into the sporangium.
Think of it as the backbone of the fruiting body — providing internal support.
Details:
Composed of dense, non-cellular material.
Extends partially or fully into the sporangium cavity.
Often continuous with the stalk, and visible as a darker or opaque core.
The columella strengthens the sporangium and serves as a structural anchor.
6. The Hypothallus — The Foundation
Beneath every fruiting body lies the hypothallus, a thin, flattened layer that attaches the structure to its substrate.
It acts as a baseplate — securing the sporangium or cluster of sporangia to bark, leaves, or wood.
Roles:
Provides attachment and sometimes contributes to nutrient transfer during sporulation.
May be membranous, shiny, or crusty depending on the species.
In some genera (e.g., Physarum), the hypothallus extends between multiple sporangia, forming a shared base.
The hypothallus anchors multiple sporangia, as seen here in Stemonitis herbatica, ontop of a brophyte.
7. The Stalk — The Supporting Column
The stalk elevates the sporangium above the substrate, helping spores catch air currents for dispersal.
It’s made of hardened material, often continuous with the columella.
️ Functions:
Increases height for better spore distribution.
Provides structural stability during drying.
Varies in length, thickness, and composition among genera.
The slender stalk elevates the sporangium, allowing spores to disperse efficiently into surrounding air currents.
8. The Spores — Carriers of the Future
At the heart of it all lie the spores — microscopic, single-celled units that ensure survival and dispersal.
They are released into the air or carried by insects, wind, or rain to new habitats.
Key Facts:
Typically 5–15 µm in diameter.
Shapes range from smooth to spiny, round to irregular.
Walls often sculptured — a major taxonomic character under microscopy.
Once settled in moist conditions, they germinate to release amoeboid cells, beginning the cycle again.
Each spore is a microscopic sphere, often 5–15 µm across, with unique ornamentation patterns that help myxomycetologists distinguish between species. In these Badhamia capsulifera spores, we seem them clustering, with ornamentation, warts, only on half of the spore body. This spore is magnified 1000x under an oil immersion slide.
Pro Tip:
Using phase-contrast or brightfield microscopy can reveal spore ornamentation crucial for identification.
9. How It All Works Together
Each part of the fruiting body has a precise function:
Peridium protects.
Capillitium controls spore release.
Columella and stalk support the structure.
Hypothallus anchors it.
Spores carry the lineage forward.
The result is a microscopic machine for dispersal — a structure optimized by evolution for both durability and delicacy.
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