You’ve heard of a sea cucumber, but how about a sea mushroom? This week, scientists described a mushroom-shaped sea creature that may be in a phylum all its own.
Two species of the newly described animal were found along the bottom of the ocean as deep as 3,200 feet beneath the surface. One is a about 10 mm in length, the other is 17 mm; both are slightly smaller than a button mushroom.
The Danish research team that described the animal named it Dendrogamma, but in a paper published in PLOS One, they acknowledge that they are having trouble deciding exactly how to categorize it. It has features similar to animals in the phylum Ctenophora (the comb jellies and their relatives) and Cnidaria (sea anemones, corals, and jellyfish), but it doesn’t fit neatly into either category.
“This is our central conundrum,” said Jean Just of the University of Copenhagen, co-author of the paper. “They are at the base of the Tree of Life together with Cnidaria and Ctenophora, but they lack the defining characteristics of those two major Phylae.”
A close look at Dendrogamma reveals a remarkably simple creature with a single opening at the base of its “stem” where food goes in and waste comes out. In the “cap” of the animal, this gastrovascular tube branches into a series of canals.
Animals in the Cnidaria phylum have tentacles, sense organs, and radiating canals, none of which the Dendrogamma has. Animals in the Ctenophora phylum have small-hair like features called cilia that help them move through the water, but Dendrogamma does not.
The authors note that in the review process it was suggested that Dendrogamma could represent a new, non-bilaterian phylum in the kingdom Animalia. “While we may agree, we refrain from erecting such a high-level taxon for the time being because new material is needed to resolve many pertinent outstanding questions,” they write in the paper.
Intriguingly, they do have similarities to an extinct group of Precambrian group of animals known as Ediacara, which also have dichotomously branching canals in the disc. However, these animals were thought to be a “failed experiment.”
Whether these two animals are related or their similarities simply represent a parallel response to the same environmental conditions is not clear.
The reseachers had a total of 18 specimens of Dendrogamma to work with when they wrote the study. They were collected in 1986 on the Australian continental slope near Tasmania as part of a research cruise.
Unfortunately, these specimens were not ideally preserved. They were accidentally kept in pure alcohol rather than 80% ethanol, which resulted in them shrinking and almost completely drying out. They are also unsuitable for molecular analysis.
“It is of course very disappointing to us, but that’s life!” Just said.
If new specimens are found, the researchers would hope to learn more about how these animals live in their natural environment, and to study their molecular an anatomical construction to see whether they have nerve endings or muscle cells.
But, that may take awhile. In the 28 years since they were discovered, no additional Dendrogammas have been found.