Phoronis ijimai
April 6, 2014

Scientists Discover First New Horseshoe Worm In Over 60 Years

redOrbit Staff & Wire Reports - Your Universe Online

A team of Japanese researchers has identified a new species of horseshoe worm, making it the 11th member of the phylum Phoronida and the first to be discovered in more than six decades.

Horseshoe worms are worm-like invertebrates that live in the water and typically make their homes in rocks, bivalve shells and other hard and soft substrates. The “horseshoe” portion of their name refers to the appearance of their lophophores, which are U-shaped crowns of tentacles that serve as the organism’s feeding organ.

The new species was collected from Tomioka Bay in Amakusa, Japan and has been identified as Phoronis emigi. It’s discovery, which is the first new horseshoe worm to be identified since Phoronis pallid in 1952, is described in the latest edition of the journal ZooKeys.

The study authors report that the number and arrangement of body-wall muscle bundles of Phoronis emigi are unlike any other horseshoe worms, as is the position of the nephridia, which served as the excretory organ of some invertebrates. In other ways, it is described as morphologically similar to the sand-dwelling Phoronis psammophila and it is also closely related to the species Phoronis hippocrepia.

Phoronis emigi is reddish in color in its living state, and yellowish white after fixation, the researchers wrote. Without the lophophore, its body is 4.42-20.06 millimeters long and 0.34-0.66 millimeters in diameter at its ampula. Its horseshoe-shaped lophophore is 2.00-3.51 millimeters long and 0.54-0.76 millimeters in diameter at its base.

In addition, the study includes the morphology of the topotypes for Phoronis ijimai more than a century after its original description. By combining detailed observations of its internal morphologies and its molecular phylogenetic analyses, they prove a long-disputed synonymy between Phoronis ijimai and Phoronis vancouverensis.

“It is necessary to use both internal anatomy and molecular data for [sic] reveal the global diversity of horseshoe worm,” explained study author Dr. Mastato Hirose of the University of Tokyo’s Atmosphere and Ocean Research Institute. “The known phoronid diversity still remains low, with all specimens reported from limited habitats and the localities by the limited reports. Investigations at new localities or habitats may yield additional species in the future.”