An international team of paleontologists has found the remains of an extinct sea cucumber in 430 million-year-old (Silurian period) fossil-rich deposits in Herefordshire, the United Kingdom.
The researchers named the new species Sollasina cthulhu due to its resemblance to monsters from the fictional Cthulhu universe created by author H.P. Lovecraft.
Although the animal was just 1.2 inches (3 cm) wide, its many long tentacles (tube feet) would have made it appear quite monstrous to other small sea creatures alive at the time. It is thought that these tentacles were used to capture food and crawl over the seafloor.
Thirteen specimens of Sollasina cthulhu were collected from a single locality of the Herefordshire Lagerstätte (a geologist’s term for a deposit of extraordinarily well-preserved fossils).
One exceptionally well-preserved specimen was selected for detailed study by physical-optical tomography.
The 3D reconstruction allowed the paleontologists to visualize Sollasina cthulhu’s internal ring, which they interpreted as part of the water vascular system — the system of fluid-filled canals used for feeding and movement in living sea cucumbers and their relatives.
“Sollasina cthulhu belongs to an extinct group called the ophiocistioids, and this new material provides the first information on the group’s internal structures,” said Dr. Imran Rahman, from the Oxford University Museum of Natural History.
“This includes an inner ring-like form that has never been described in the group before. We interpret this as the first evidence of the soft parts of the water vascular system in ophiocistioids.”
The new fossil was incorporated into a computerized analysis of the evolutionary relationships of fossil sea cucumbers and sea urchins.
The results showed that Sollasina cthulhu and its relatives are most closely related to sea cucumbers, rather than sea urchins, shedding new light on the evolutionary history of the group.
“We carried out a number of analyses to work out whether Sollasina cthulhu was more closely related to sea cucumbers or sea urchins,” said Dr. Jeffrey Thompson, from University College London.
“To our surprise, the results suggest it was an ancient sea cucumber.”
“This helps us understand the changes that occurred during the early evolution of the group, which ultimately gave rise to the slug-like forms we see today.”
The team’s paper was published in the journal Proceedings of the Royal Society B: Biological Sciences.
Imran A. Rahman et al. 2019. A new ophiocistioid with soft-tissue preservation from the Silurian Herefordshire Lagerstätte, and the evolution of the holothurian body plan. Proceedings of the Royal Society B: Biological Sciences 286 (1900); doi: 10.1098/rspb.2018.2792