A sea whelk is a type of sea snail that is purple in color with light tangerine shells that are the shape of a cone with orange spikes on them. They also have no eyes and a big gaping mouth that can spit out lavender slime bubbles.
Role in episode
During "Whelk Attack," Bikini Bottom sustains devastation due to giant whelks. It is later revealed that germs caused the whelks to be aggravated.
They resemble a regular sea snail without the stems leading up to the eyes and the eyes themselves. While the bodies are purple, their shells feature a light tangerine color with a circular series of spikes around each curve on the cone shell. Throughout the episode, these snails are depicted as giants, but they can actually fit in the palm of a fish's hand.
Sea whelks have a disease (most likely a bunghole parasite) that aggravates the whelks, causing a rampage while being huge in size.