In a day and age when it seems like so many species are becoming endangered or going extinct, it's a welcome celebration when 17 new species of an animal are discovered — especially ones as bright and colorful as these sea slugs.

These sea slugs, also known as nudibranches, live in coral reefs across the Indo-Pacific region.

A team of researchers led by Terry Gosliner from the California Academy of Sciences analyzed a variety of images of nudibranches from the genus Hypselodoris, detailing their behaviors and mating habits. Studying the color and anatomy of these nudibranches, the research team reorganized the family tree after they determined that there were 17 new species in the Hypselodoris family. They published their findings in the Zoological Journal of the Linnean Society.

"When we find an anomaly in color pattern, we know there’s a reason for it," said lead author Hannah Epstein, former California Academy of Sciences volunteer and researcher at James Cook University in Australia. "It reveals a point in evolution where a selective pressure — like predation — favored a pattern for camouflage or mimicking another species that may be poisonous to would-be predators."

yellow and maroon sea slug
Hypselodoris iba (Photo: Terry Gosliner/California Academy of Sciences)
various shades of purple sea slug
Hypselodoris iba (Photo: Terry Gosliner/California Academy of Sciences)

One example of color anomalies are the two Hypselodoris ibas pictured above. For years, scientists believed they were two different species. The lavender iba was believed to be Hypselodoris bullocki until a photographer captured an image of two mating. Gosliner's team studied the image and determined that they were, in fact, the same species but with different color tones and patterns.

"When two different species like H. iba and H. bullocki present in the same color, the simplest explanation is that they share a common ancestor," said California Academy of Sciences Dr. Rebecca Johnson. "These two species, however, are pretty far apart on the family tree: the more likely explanation for their similar appearance is that they reside in the same geographic region where being purple is advantageous for avoiding predators either as camouflage or warning of distastefulness."

The team assembled the rest of the recently discovered species into different "color trees" to better understand how evolution affects their vibrant colors.

"Sea slugs have an arsenal of strategies for surviving, from mimicry to camouflage to cryptic patterns," said Gosliner. "We’re always thrilled to discover new sea slug diversity. Because nudibranchs have such specialized and varied diets, an area with many different species indicates a variety of prey — which means that coral reef ecosystem is likely thriving."

The other nudibranches can be seen below in their full technicolor glory.

yellow and blue dot sea slug
Hypselodoris confetti (Photo: J. Goodheart)
teal sea slug
Hypselodoris melanesica (Photo: Terry Gosliner/California Academy of Sciences)
royal blue sea slug
Hypselodoris variobranchia (Photo: Terry Gosliner/California Academy of Sciences)
orange spikes sea slug
Hypselodoris peri (Photo: Terry Gosliner/California Academy of Sciences)
red sea slug
Hypselodoris rositoi (Photo: Terry Gosliner/California Academy of Sciences)
white sea slug
Hypselodoris lacuna (Photo: Terry Gosliner/California Academy of Sciences)
orange sea slug
Hypselodoris alburtuqali (Photo: Terry Gosliner/California Academy of Sciences)
white, yellow and violet sea slug
Hypselodoris cerisae (Photo: Rie Nakano)
juniper sea slug
Hypselodoris juniperae (Photo: Terry Gosliner/California Academy of Sciences)
orange striped sea slug
Hypselodoris katherinae (Photo: Terry Gosliner/California Academy of Sciences)
light pink sea slug
Hypselodoris paradisa (Photo: Vanessa Knutson)
black and yellow sea slug
Hypselodoris roo (Photo: Terry Gosliner/California Academy of Sciences)
beige lines sea slug
Hypselodoris skyleri (Photo: Terry Gosliner/California Academy of Sciences)
brown sea slug
Hypselodoris yarae (Photo: Terry Gosliner/California Academy of Sciences)
white and purple sea slug
Hypselodoris brycei (Photo: Nerida Wilson)