Unidentified ‘Butterfly’ Palthoas.

Recently while diving off of Key West, I was fortunate to come upon a rare and unidentified species of Palythoa. This was the first time that I have come upon this type in five years of frequent diving throughout the Florida Keys. Apparently it is less rare elsewhere in the Caribbean, but as of now has yet to be properly identified by a zoanthid taxonomist. On its particular patch of reef it was relatively abundant, despite being completely absent in seemingly identical reefs in the surrounding area. And while it might seem logical that it only takes one lucky zoanthid larvae to ultimately colonize a large area, it seems that there were at least 2 separate morphs cohabiting the area, which makes its complete absence from other nearby reefs compelling. And while Caribbean Palythoa display morphologies that seem to overlap, these particular Palythoa have a few traits that make it noticeably distinct:

• Small size (1/4″-3/8″ disc diameter)
• Translucent oral disc, often with teal-bluish iridescent sheen
• Distinctive white splotch, often butterfly shaped
• Eyelash-like tentacles

But considering that the morphologies of Caribbean Palythoa species seem to blur together, genetic analysis will be the most reliable way to determine species-hood. Fortunately our friend James Reimer is a zoanthid expert in Japan’s Ryuku Islands with access to such equipment and expertise. In addition to sending him samples of this Palythoa morph, we will also include a variety of other local Palythoa morphs to see just how distinct the individual species are.

One of the first presentations that I caught today at the ICRS focused on the genetic analysis of Indo-Pacific and Caribbean zoanthid species. The work was performed and presented by Dr. James Reimer, a zoanthid specialist at the University of the Ryukus in Japan. If you’ve ever spent any time on CoralPedia.com (formally Zoaid.com), you might be familiar with Dr. Reimer and his work. Take a look here to see his photo gallery.

For Indo-Pacific species he analyzed Zoanthus vietnamensis and Z. sansibaricus. For Caribbean species he analyzed Z. sociatus and Z. pulchellus. His findings revealed that Z. vietnamensis and Z. sociatus were genetically similar enough to be considered part of the same closely related clade (a taxonomic group with a common ancestor). Similarly, Z. sansibaricus and Z. pulchellus were shown to be grouped together in another clade. This suggests that at one time in the Earth’s history, these two pairs of zoanthid species were at one time the same species (Z. vietnamensis= Z. sociatus, Z. sansibaricus= Z. pulchellus). The separation of the species occurred when the isthmus of Panama closed about 3 million years ago.

Further genetic analysis of the Symbiodinium sp. (zooxanthellae) from Z. vietnamesis and Z. sociatus showed that these two species share identical symbiotic zooxanthellae, despite at least 3 million years of geographic isolation in different oceans. The same was true when he compared the zooxanthellae from Z. sansibaricus and Z. pulchellus. Dr. Reimer believes that the separation and development of the current species occurred about 6.5-7 million years ago.

Additionally, the two clades are similar enough with each other that genetic similarity suggests that all four current species shared a single common ancestor about 15 million years ago.

I asked Dr. Reimer if he had had a chance to compare the DNA from Caribbean and Pacific specimens of Zoanthus gigantus (known in the hobby as “People Eaters”). Unfortunately, he only has one sample of Caribbean Z. gigantus, and therefore hasn’t been able to do the appropriate analysis. To overcome this hurdle, we have offered to help supply him with these and other Caribbean zoanthids for future studies.