Home » Teaching at UH West O'ahu » Animal Regeneration: The Magical Planaria

Animal Regeneration: The Magical Planaria

This week in my intro bio class, we are learning about the regenerative capabilities that some animals exhibit. For example, many species of lizard are able to lose their tail to a predator and regrow it over the course of several weeks/months (though it will regrow with cartilage instead of bone). Salamanders are even capable of regrowing an entire limb, bone and all.


Planaria prior to cutting (left), and after regeneration (right)

My personal favorite, though, are planaria.  These flatworms can regenerate their entire body from 1/279th of their total tissue. That means you can cut a single half-inch-long planaria into TWO HUNDRED SEVENTY NINE pieces, and each one will regenerate a whole, fully functional planaria in a few weeks. You can cut them in half and the head end will grow a new tail and the tail end will grow a new head. You can cut them lengthwise and the right side will grow a new left and the left side will grow a new right. You can even cut them lengthwise just through the head end, and it will grow two full heads! You can do the same through the tail end and end up with a two-tailed planaria. If you’re really good with a scalpel, you could even make your very own Lernaean Hydra, to fight a very tiny Hercules.

Before you can marvel at the regenerative capabilities of LIVE planaria in your very own biology classroom, though, we have to get our hands on some. So today, UHWO lab manager Carrie Tome and I headed over to Sumida Farm to collect some! Sumida is a 10-acre watercress farm tucked between Kamehameha Highway and the Pearlridge Mall in Aiea, which by itself supplies 70% of Hawaii’s watercress.


The watercress doesn’t grow in soil, but rather in rocky beds submerged in spring water from the nearby Pearl Harbor Spring. It is in the rocky pools surrounding the watercress that Carrie and I harvested the planaria. It was surprisingly easy to find them. You could pick up any little rock in the pools and it would likely have a few planaria stuck to the underside. We just gently washed them into a tub to bring back to campus. I took a couple pictures of them in their new homes because they are just so cute! I mean, look at those eye spots – they’re like little cartoon worms!

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Tomorrow in class, we will… uh… surgically alter them, and then come back next week to see how much has regenerated. Check back here for some cool before-and-after pictures!

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