Unknown Parents – Mysterious Larvae Found in Panama's Two Oceans

In the microscope, seawater reveals the larval stages of little-known marine creatures called phoronids (horseshoe worms), but finding their parents is another story. Although such fanciful larvae have attracted the attention of scientists who study plankton – the tiny plants and animals drifting from the world's oceans – in the early nineteenth century were only fifteen or so species of phoronids known in the world , based on adult specimens. A study of phoronid larvae published this week by scientists at the Smithsonian Tropical Research Institute (STRI) in Panama found eight potentially new species.

"The global diversity of small, rare marine animals such as phoronids is largely underestimated," said Rachel Collin, researcher at STRI. "We do not know what animals are and we know even less about their role in the world's oceans."

Because Phoronidae larvae swim and drift in seawater, they are much easier to sample than their adult forms, which live on the bottom of the sea, in sand, sediment or rubble. And the larvae do not look like adults, making it difficult to know which larva belongs to which adult without doing some sort of paternity test: comparing larval DNA sequences to the DNA of their potential parents.

Named in honor of the Egyptian goddess Phoronis, this horseshoe-shaped adult tubular worm anchors its body in rocks or corals and waves a crown of ciliated tentacles to capture tiny particles of food. To reproduce, their eggs and sperm unite to create embryos that hatch into swimming larvae, which then become members of the microscopic plankton. The larvae have a cylindrical body surmounted by a ring of tentacles and a large cap used to capture food. Many are decorated with yellow pigment spots and in some, it is possible to see spots of red or pinkish blood cells through their translucent bodies. Finally, they descend to the sea floor, become adults and end their life cycle, considered the most common cycle in the animal kingdom.

Scientists collected plankton in Panama Bay on the Pacific coast and Bocas del Toro on the Caribbean coast. By examining the plankton with a stereomicroscope, they found more than 50 phoronid larvae; 23 from the Pacific and 29 from the Atlantic. Using a genetic technique called barcode based on DNA sequencing, they were able to distinguish three distinct phoronids in the plankton of Panama Bay and four other Caribbean.

The DNA of particular genes from each of these animals was different from anything recorded in GenBank, a global DNA collection of more than 300,000 organisms, suggesting that these larvae might belong to species news for science. However, finding adults of these species may take years, especially since very few scientists study horseshoe worms.

"Because of the cryptic lifestyles of phoronids, the corresponding adult worms can never be found, but the presence of their larval forms in the plankton confirms that they are here, established and in the process of breeding", said co-author Michael J. Boyle, previously. Tupper postdoctoral researcher at STRI, now a biologist and senior researcher in the Life Stories program at Smithsonian Marine Station in Fort Pierce, Fla.

At the STRI Research Station on Bocas del Toro in the Caribbean, Collin, the station's director, is organizing a series of training courses on tropical taxonomy, designed to bring researchers specialized in these organisms and others marine organisms quite unknown in Panama, where they almost always discover new species and pass on their knowledge to students. They produce a series of videos on YouTube to teach students how to capture, preserve and identify new species.