“…and today we’re talking about a flat character. But more on that later.”
Everyone likes a comeback kid. Clutching victory from the jaws of defeat. But what the Black Planarian Flatworm does is way beyond a come from behind win. This pond citizen has a regenerative ability so extraordinary that it would give a thinking creature a ship-of-theseus style identity crisis. Sometimes that’s what it takes to survive in Life, Death, and Taxonomy.
Measure Up
Welcome to the beloved Measure Up segment. The official listener’s favorite part of the show! The part of the show when we present the animal’s size and dimension in relatable terms through a quiz that’s fun for the whole family. It’s also the part of the show that’s introduced by you when you send in audio of yourself saying, singing, or chittering the words Measure Up into ldtaxonomy at gmail dot com.
In Media: In J.K. Rowling’s Harry Potter series, Flobberworms are dull, worm-like magical creatures resembling flatworms in their simple, soft-bodied structure. They are mentioned in Harry Potter and the Prisoner of Azkaban as creatures studied in Care of Magical Creatures class. They’re described as sluggish, mucus-producing worms that live in damp environments, loosely echoing the aquatic habitats of flatworms like Polycelis nigra.
Length of Polycelis nigra
Polycelis nigra has a length of 12 mm (0.47 inches). How many flatworms, laid end to end, fit into the length of these freshwater-related objects from Europe or North Africa?
Question: How many Polycelis nigra fit into each object’s length?
A) 11 go into the length of a European freshwater pearl mussel
B) 20 go into the diameter of a water lily leaf
C) 5 go into the length of a North African newt
a) The length of a European freshwater pearl mussel
The European freshwater pearl mussel (Margaritifera margaritifera), found in clean rivers across Europe, reaches about 12 cm (120 mm or 4.72 inches) in shell length for a large adult.
b) The diameter of a water lily leaf
The white water lily (Nymphaea alba), common in European lakes and ponds, has floating leaves with a diameter of about 25 cm (250 mm or 9.84 inches) for a mature plant.
c) The length of a North African newt
The Algerian ribbed newt (Pleurodeles nebulosus), native to North African freshwater habitats, has a body length of about 8 cm (80 mm or 3.15 inches), excluding the tail, for a large adult.
Weight of Polycelis nigra
Polycelis nigra weighs 1 milligram (0.001 grams). How many flatworms fit into the weight of these freshwater-related objects from Europe or North Africa?
Question: How many Polycelis nigra fit into each object’s weight?
A) 100,867.0 go into the weight of a European water vole
B) 100,400.0 go into the weight of a papyrus scroll
C) 59.0 go into the weight of a freshwater shrimp
a) The weight of a European water vole
The European water vole (Arvicola amphibius), a rodent found in European rivers and wetlands, weighs about 200 grams (0.2 kg) for an average adult.
b) The weight of a papyrus scroll
A papyrus scroll, made from the Cyperus papyrus plant used in ancient North African (Egyptian) writing, weighs about 100 grams (0.1 kg) for a medium-sized scroll, based on archaeological estimates.
c) The weight of a freshwater shrimp
The European freshwater shrimp (Gammarus pulex), common in rivers and streams, weighs about 50 milligrams (0.05 grams) for a large individual.
Key Features of Polycelis nigra
- Habitat: Found in clean, oxygen-rich freshwater environments like streams, ponds, and springs across Europe and parts of Asia. It thrives in moist substrates like moss or sediment.
- Diet: Predatory, feeding on small invertebrates (e.g., nematodes, microcrustaceans) using an eversible pharynx to capture prey and secrete mucus to immobilize it.
- Reproduction: Capable of both asexual reproduction (via fission, splitting into two) and sexual reproduction (hermaphroditic, laying eggs in cocoons).
Major Fact: Talkin About Regeneration
Polycelis nigra is renowned for its ability to regenerate complete organisms from small body fragments, a process driven by its unique biology. Here’s how it works:
- Neoblasts: The Regeneration Powerhouse
- What Are Neoblasts?: Neoblasts are pluripotent stem cells, unique to planarians, that make up ~20–30% of the worm’s body cells. These cells are distributed throughout the body and are responsible for regeneration and tissue maintenance.
- Role in Regeneration: When Polycelis nigra is injured or cut, neoblasts rapidly divide and migrate to the wound site. They differentiate into various cell types (e.g., neurons, muscle, epidermis) to rebuild missing tissues.
- Mechanism: After amputation, neoblasts form a blastema, a mass of undifferentiated cells at the wound site. The blastema develops into the regenerated structures, guided by molecular signals.
- What Are Neoblasts?: Neoblasts are pluripotent stem cells, unique to planarians, that make up ~20–30% of the worm’s body cells. These cells are distributed throughout the body and are responsible for regeneration and tissue maintenance.
- Regenerative Capacity
- Polycelis nigra can regenerate a complete body from fragments as small as 1/100th of its original size. For example:
- A head fragment can regrow a body and tail.
- A tail fragment can regrow a head, including the brain and eyes.
- Middle fragments can regenerate both head and tail.
- A head fragment can regrow a body and tail.
- Regeneration typically takes 1–2 weeks, depending on the fragment size and environmental conditions (e.g., temperature, food availability).
- Polycelis nigra can regenerate a complete body from fragments as small as 1/100th of its original size. For example:
- Polarity and Body Plan
- Polycelis nigra maintains a clear anterior-posterior (head-to-tail) axis during regeneration. This is guided by bioelectric signals and molecular gradients, ensuring the correct structures form in the right places.
- For example, if cut in half, the anterior piece regenerates a tail, and the posterior piece regenerates a head, restoring the original body plan.
- Environmental and Physiological Factors
- Nutrition: Regeneration is energy-intensive, and well-fed Polycelis nigra regenerate faster. Starved individuals can still regenerate by reallocating body resources, sometimes shrinking in size.
- Temperature: Optimal temperatures (around 15–20°C) enhance regeneration speed, while extreme conditions slow it down.
- Wound Healing: Immediately after injury, the wound closes within hours via muscle contraction and epidermal spreading, setting the stage for neoblast activity.
Interesting Facts About Polycelis nigra Regeneration
- Head Regeneration: A headless Polycelis nigra can regrow a functional brain within days, restoring behaviors like feeding and light avoidance.
- Memory Retention: Some studies on related planarians suggest regenerated worms retain learned behaviors, hinting at memory preservation in neoblasts or neural networks.
- Asexual Advantage: In asexual reproduction, Polycelis nigra splits into two, and each half regenerates the missing parts, effectively cloning itself.
Resilience: Even under stress (e.g., starvation), Polycelis nigra can regenerate by reallocating resources, a process called “degrowth.”