The Planarian

Posted in Insects, Nature Articles

planaria picBliss is floating on an air mattress, drifting on the shallow waters of the Eel River. Excitement is seeing a planarian undulating across the gravel.

It stared at me. I stared at it.

The planarian is a small (1/2” or less) and simple flatworm. It lives in rivers, freshwater ponds and saltwater, gliding across the bottom as it looks for prey (small worms, crustaceans) . The two eyespots are sensitive to light, which the planarian prefers to avoid. On the sides of its triangular head, the “ears” are actually sensitive to touch and to chemicals.

On its belly is the mouth. The planarian extend its long tubular pharynx out through the mouth and secretes digestive enzymes. These begin to chemically break up the prey. The pharynx then sucks up the bits. These go into a simple gut. The intestinal cells lining the gut complete the digestion. Nutrients are dispersed throughout the body by a highly branched system of tubes. Excretory pores along the sides release the chemical waste products.

Planaria breathe through their skin, receiving oxygen and releasing carbon dioxide. They move by the beating of small hair-like projections from the cells on their bellies, or via muscle contractions. The muscles are a part of the body membrane. The nervous system is very simple: two large bodies of nerve cells (ganglions) behind the “ears”, and nerve cords and smaller ganglions in a ladder-like configuration down the body.

They are hermaphrodites, having both testes and ovaries, but they must mate to reproduce, exchanging each other’s sperm. The eggs develop internally, are shed in capsules, and several weeks later hatch into mini-adults.

So why was I excited to see one? The last time I saw one was in a biology class, in a petri dish, where it was being cut in half. Planaria have the amazing ability to regenerate missing parts. You could cut one up into over 100 pieces and each one would grow into an intact, fully functional planarian. How does this happen? About one fifth of the cells in its body are stem cells, capable of making any of the various tissues and organs, much as the cells of an early embryo (embryonic stem cells) can do.

Today, researchers studying planaria have identified a protein, TOR, which is essential for regeneration. Without it, no growth can occur. Researchers are looking for ways to inactivate TOR in cancer cells, to stop them from multiplying and to activate TOR where needed to stop degeneration caused by disease or Alzheimer’s.

Eve Broughton was educated at UC. Berkeley and lives in Whitethorn.

 

Water Penny Beetles

Posted in Fauna, Insects, Nature Articles

Psephenus_herricki,I_DSC48“Grandma, what’s this?” Danged if I knew. Bella and I were looking for aquatic insects in the Mattole, and she had captured something very weird in the clear magnifying box. We couldn’t find its photo in Audubon’s Field Guide to North American Insects and Spiders.

What she had captured was really strange: small, and copper-brown, it was shaped like a flat limpet and segmented like a chiton. By using a magnifying lens on top of the box’s magnification, we could see a mandible, legs and moving gills on its underside. I got the identification several days later from Pete Haggard, entomologist: Water Penny Beetle larva.

It was a fortuitous find. These larvae are only found in clean, well-oxygenated, unpolluted water. They prefer fast-moving water, clinging to the underside of rocks, and avoid habitats heavily covered with algae or inorganic sediments. They breath oxygen through their paired feathery gills, rely on claws on their legs for rock-clinging, and move away from light, preferring the undersides of the rocks . The larval water pennies scrape the thin layer of algae, microorganisms and feces from the surface of the rocks with their mandibles and eat this. The penny-like shape is created by flattened dorsal (back) plates which expand out to widen the sides. The one Bella found was slightly over ¼” long.

Water penny adult, photo by Joyce GrossThe larvae grow and molt several times during the summer, and then they create a small chamber in moist soil on land, where they, still in their larval skins, pupate and transform into the adult. The adults are small (less than ¼”), dark, with short fine antennae and a slightly flattened body. They breathe air and live on land close to the water. The adult water penny beetle survives for just a short time, 2 to 3 weeks, and may not even eat during this phase. Like many other insects with an aquatic phase, they exist to procreate.

Play behavior on wave-splashed rocks has been observed before mating. Fertilization is internal (inside the female’s body). The female lays small, bright yellow eggs, hundreds of them, on the edge of the stream, or submerged objects in stream riffles. The newly hatched larvae crawl into the water to repeat the cycle. Next summer, we might find another one.

 

Written by Eve Braughton. Eve lives in Whitethorn and was educated at UC Berkeley

 

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