‘Cryptic’ sea creature — covered in odd-shaped growths — discovered as new species
On a coral reef in Thailand, an “extremely cryptic” sea creature munched away on its favorite food. The animal blended in with its surroundings and seemed easy to overlook.
Still, something about the weird-shaped animal caught the attention of scuba-diving scientists — and for good reason. It turned out to be a new species.
Researchers conducted over 100 surveys of coral reefs around Koh Tao island between 2018 and 2020, according to a study published Jan. 24 in the journal Symbiosis. The goal of the surveys was to study the relationship between corals and gastropods, an animal group that includes sea snails and sea slugs.
During the survey, researchers encountered some “cryptic” sea slugs they couldn’t identify, the study said. They captured four of these animals and, taking a closer look, realized they’d discovered a new species: Phestilla arnoldi, or Arnold’s sea slug.
Arnold’s sea slugs measure about a tenth of an inch in length, researchers said. They are “the smallest known Phestilla species” and “among the smallest known” sea slugs.
.jpg "Rahul Mehrotra (1).jpg")
Photos show an Arnold’s sea slug. It has a creamy body with some yellow and white blotches. Its head has four smooth horn-like tentacles, and its tail tapers to a point.
Several odd-shaped growths, known as cerata, jut out of the sea slug’s back and side. Each growth has two bulges and looks almost like an observation tower.
.jpg "Rahul Mehrotra (2).jpg")
Arnold’s sea slugs live on a specific type of coral, Acropora muricata, commonly called staghorn coral, between depths of about 10 to 30 feet, the study said. The new species feeds off this coral and lays its eggs on it in the form of “spawn capsules.”
Researchers described the new species as “extremely cryptic.” A photo shows how well the sea slug blends into the coral.
Rahul Mehrotra, one of the study’s co-authors, told McClatchy News that this research “was among the most challenging works because of the incredibly small size of the species, making it a surprising find in the water.”
.jpg "Celicia Cordes (2).jpg")
Researchers said they named the new species after Spencer Arnold “for his discovery of this highly cryptic species” and for supporting “marine biology education and research.”
So far, Arnold’s sea slugs have only been found around Koh Tao island, but researchers suspect it is more widespread, the study said. Koh Tao, or Ko Tao, is a small island on the western side of the Gulf of Thailand. The island is about 260 miles southwest of Bangkok.
The new species was identified by its size, teeth, body shape, internal anatomy and preferred food, the study said. DNA analysis found the new species had at least 9% genetic divergence from other Phestilla sea slugs.
The research team included Rahul Mehrotra, Manuel Caballer, Deepeeka Kaullysing, Suthep Jualaong and Bert Hoeksema.
CORRECTION (2/1): The DNA analysis was not included in an earlier version of this article. The corrected story is above.
This story was originally published January 31, 2024 at 9:14 AM with the headline "‘Cryptic’ sea creature — covered in odd-shaped growths — discovered as new species."
