Introducing Sterechinus

One of the most exciting parts of the Icy Inverts cruise has been seeing, in real life, all of the interesting animals that I previously only had seen in articles and PowerPoint slides. Seeing these cool animals has been one of the more thrilling parts of this cruise. So, there are many animals I could tell you about, but today I want to put the spotlight on a particular group of animals that I personally pay quite a bit of attention to–the Sterechinus sea urchins.
 
Sea urchins are echinoderms, meaning that they more closely related to sand dollars, sea cucumbers, sea stars, and feather stars than any other extant organism. Sea urchins are among the earliest animal to be used to understand embryonic development. As a developmental model organism, they help us study how the animal form is derived from a single cell. Despite their round and spiny look as adults, sea urchin embryos share many features with vertebrate embryos. They develop certain embryonic structures in the same order as vertebrates do and are similarly bilaterally symmetrical. In more recent times, we’ve learned that sea urchin embryos use many of the same molecular mechanisms to grow as vertebrate embryos do. Back home at Auburn, I spend most of my lab time studying the embryonic development of a sea urchin that lives off the west coast of California, the purple sea urchin.
 
Sterechinus is the genus name of at least two species of sea urchins found only in the Southern Ocean, Sterechinus neumayeri and Sterechinus antarticus. Sterechinus are of particular interest to us because they develop similarly to other sea urchin species, except very, very slowly. For example, while the species I work with by home takes about 15 hours to reach what we call the ‘hatching’ stage, Sterechinus take almost a full week to reach that same stage. Naturally as scientists, we want to understand why, and this cruise gives us a chance to explore such questions in depth.
 
Throughout most of the cruise, I have been working with Sterechinus neumayeri which have a bright red coloration (see pictures). I keep them in a cold-room in the ship called Big Antarctica, where we keep them close to their natural temperature at around 0° C. Since we replicate their natural conditions as much as possible, we get to see some of their interesting behaviors. Like other sea urchins, Sterechinus use their tube feet to get around. They pump water into their tube feet to help extend them past theirs spines. And then use suckers at the ends of their tube feet to grab on to things, like the aquarium glass. Candace and I placed some red algae in the tank with them, and these urchins wasted no time munching on it, and even wearing it around! In some of the pictures you can see one fashionably dressed in the red algae. It is not clear really why they do this, but this behavior could help them hide from threats in the wild, as these little urchins make themselves look like some unassuming red plant on the seabed.

Che Ka
PhD student
Auburn University