Re: do male and female sea stars look different?

Hello Starr,

When male and female animals of the same species look different, we biologists call that sexual dimorphism. You can see sexual dimorphism for yourself in many birds and fishes, where the males are more brightly colored while females tend to have dull coloring. In species such as mallard ducks and guppies, it is easy to distinguish between males and females.

However, sexual dimorphism does not occur in sea stars, and you can't tell if an individual star is male or female just by looking at it. The only way to know for sure is either to induce it to spawn or wait for it to spawn naturally, and look at the gametes -- males will spawn milky whitish sperm, and females will spawn larger, granular eggs. I did find a scientific article on sexual dimorphism in a species of brittle star, but this species appears to be the exception to the rule that echinoderms are not sexually dimorphic.

The sea star that you have chosen for your project, the blue sea star, does have some very interesting capabilities. Members of this genus, Linckia, can reproduce by tearing their bodies apart, with each part developing into a new star. Here's a link to a previous MadSci answer about this very subject.

I hope this answers your question. Good luck on your project!

Allison J. Gong
MAD Scientist