CreatureCast – Pyrosomes

posted by Casey Dunn / on August 19th, 2014 / in Chordates

Anna Zeidman introduces pyrosomes, “fiery bodies” that create brilliant underwater light shows and grow into giant swimming colonies. We originally posted this episode at the New York Times, where you can read more.

This episode of CreatureCast was narrated by Samuel Lanier. The music is by Lee Rosevere.

The Vertebrate Vascular System

posted by Casey Dunn / on October 12th, 2012 / in Vertebrates
Christine Janis, a professor in the Department of Ecology and Evolutionary Biology here at Brown, designed these wonderful animations of vascular systems in vertebrates. Taken together, they provide a clear picture of the evolution of the vascular system, and place our mammalian vascular system in a much broader evolutionary context.
These animations were created in collaboration with Giovanna Roz Gastaldi and Ed Casey of Brown’s Instructional Technology Group, along with student technology assistants.

CreatureCast – Moray Eel

posted by Sophia Tintori / on December 1st, 2010 / in Podcast (Student Contribution), Vertebrates

Here is the first of this semester’s creaturecasts from the students in Casey Dunn‘s Bio 0410 Invertebrate Zoology class here at Brown. Students in this class have the option of making a creaturecast episode for their final project. This one from Phil Lai introduces the Moray Eel and describes the amazing way they eat.

This video was drawn and edited by Phil, and  is released under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 license.


Salty Pups

posted by Sophia Tintori / on June 23rd, 2010 / in Chordates, Extremophiles

In Death Valley, life can be difficult.  One might think that such a dry area would be a bad place for fish to live, and it is. But that is exactly why it is such a great habitat for this particular fish, Cyprinodon salinus, as well as the other desert pupfishes.

The salt creeks and pools of the California desert evaporate quickly, making their salinity change day by day. In the winter some creeks will be essentially freshwater, while in the hottest parts of the summer the water can become twice as salty as the ocean. Because the desert pupfish can handle this kind of fluctuation, which would kill most of the rest of us, they usually get the creek to themselves, with no other competing fish.

Some desert pupfishes in South America even live in ponds that dry up entirely during the summer. They lay their eggs in the mud before it dries, then when the rain starts to fall again, the population is reconstituted and the eggs begin to hatch.

This past March, while visiting Death Valley with his family, Casey Dunn, the principle investigator of our lab at Brown University, visited a salt water creek and found these pupfish spinning around each other while mating. The females are the smaller ones, and they lay one egg at a time. A male will swim up next to her, they will both curve their bodies into an S shape, the female drops an egg into the male’s fin, he fertilizes the egg, then drops it on the floor of the creek. In this clip the males are tagging off, each taking turns fertilizing eggs as they come out of the females.

This video is released under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 license. Thanks to Maria Dzul for pointing me towards some information about desert pupfish. Here is a paper about pupfish and the fluctuating salinity of their water, here is a description of C. macularius‘ mating behavior, and here is a nice book about California fish, which might be at your local library.

The art of knotting

posted by Stefan Siebert / on November 27th, 2009 / in Chordates

Hagfish have a skull, but no spine. They diverged from vertebrates prior to the origin of many other structures that are widespread within the group, including jaws. Hagfish are extremely important for understanding the origins of these key structures, but they are also famous for an unusual behavior—tying themselves in knots.

Hagfish have an eel-like body. They lead a bottom dwelling life and have a great sense of smell, but lack well developed eyes. When stressed, hagfish release a secretion that contains special filaments from glands along the body. When it contacts water, this secretion forms a massive slime and makes the hagfish an unpleasant bite for potential predators. To sneak out from this slimy shelter, the Atlantic hagfish, Myxine glutinosa, makes knots, which wring off the layer of slime. The knot, traveling along the body column, can provide a surface for the hagfish to push off. This enables the animal to pull its body out of the hole it makes in it’s prey’s flesh, or escape the grasp of a scientist.


Pictured above are the heads of two Atlantic hagfish, whose bodies are burried in soft sediments. They were caught in the Gullmarfjord on the Swedish Westcoast.

Photo and video by Stefan Siebert. Video edited by Sophia Tintori. “I’m learning a song for Christmas” from Jack Pleasants.

Star colonies of sea squirts

posted by Perrin Ireland / on November 17th, 2009 / in Chordates, lifecycles


Botryllus schlosseri is a colonial tunicate (or sea squirt), so named because it lives in colonies that are communally covered by a leathery tunic. Its larvae bear a striking resemblance to vertebrates, and are even called tadpoles. The resemblance is not superficial or coincidental, tunicates and their kin are the closest living relatives of vertebrates. Each tadpole attaches itself to a rock, pier, or other hard surface in the sea, and metamorphoses into a sack-like adult that will spend the rest of its life stuck in that one spot.

Tadpoles are produced sexually–they arise from an egg that is fertilized by a sperm. Like many other animals, though, Botryllus also reproduces asexually by budding off clones of itself. Each adult (also called a zooid) produces a bud, and this bud in turn begins producing another bud even before its own heart begins to beat. These clones remain attached to each other in a star shaped group with common central opening, called a siphon, and continue to share resources through their connected circulatory systems. Once the colony is large and robust enough, usually with 5 to 10 members, each adult forms a pair of ovaries and testes, and the next generation of tadpole larvae can be produced.

This is the first in a series of illustrated lifecycles I’ll be posting to CreatureCast.