Bat star

Natural History

Bat stars come in a wide variety of solid and mottled colors, including red, orange, yellow, brown, green and purple. They have webbing between their short, triangular arms, which gives them a batlike look. Normally, bat stars have five arms, but they occasionally have as many as nine arms.

Gill-like structures on a sea star's back, which aid with breathing, give its skin a fuzzy appearance. Most sea stars have pincers (pedicellariae) that remove debris from the skin gills, but bat stars have no pincers and are free of debris. Perhaps small, beating hairs (cilia) cause a water current that keeps the skin surface clean.

Bat stars have sensors at the end of each arm that sense light and detect prey. When a bat star finds a food item, it extends its stomach over the prey and oozes its digestive juices onto it, liquefies the prey meal and then slurps up the resulting "soup."


As scavengers, bat stars play an important role in the ecosystem, helping clean dead animals and algae from the seafloor. Fortunately, more and more people know that we all depend on healthy oceans, and that the survival of ocean animals, including bat stars, is up to us. Working together, we'll discover better and better solutions to pollution, overfishing and other threats to the oceans.

Cool Facts

When two bat stars bump into each other, a gentle brawl begins. They seem to be "arm wrestling" in a slow motion skirmish. Each sea star tries to get its arm on top of the other's arm. A winner isn't apparent, and perhaps to the bat stars, the brawl isn't gentle! Bat stars reproduce by spawning. The male broadcasts sperm and the female broadcasts eggs from pores near the bases of their arms. Fertilization takes place in the sea, and currents carry the young to new homes.

Annelid worms (Ophiodromus pugettensis) live in the arm (ambulacral) grooves on a bat star's mouth (oral) side. Here the worms have a plentiful supply of leftover food bits. As many as 20 worms may live on one bat star, but they don't harm the bat star—this is known as commensal symbiosis.

Sea stars have external hard parts (exoskeletons) made up of little plates (calcified ossicles) joined by connective tissue. The bat star's ossicles are so large and defined that they look like rough shingles. These shingles act like armor and protect the bat star's vital organs.