A new species of symbiotic flatworms,Paracatenulagalateiasp. nov. (Platyhelminthes: Catenulida: Retronectidae) from Belize (Central America)

Researchers have discovered a new species of symbiotic flatworm, Paracatenula galateia, in the shallow back-reef sands of Belize's Barrier Reef. This mouthless marine catenulid platyhelminth stands out due to its large size, ribbon-shaped body, and unique bipartite inclusions interpreted as sperm, distinguishing it from other members of the genus. The worms host intracellular bacterial endosymbionts, likely sulfur-oxidizing chemoautotrophs, which inhabit a specialized 'trophosome region' behind the brain while leaving the anterior rostrum bacteria-free. Phalloidin staining revealed intricate subepithelial muscle systems and dorsoventral fibers, while serotonergic nervous system mapping identified a brain at the base of the rostrum and longitudinal fibers extending both anteriorly and posteriorly, with a concentration in the 'dorsal cord.' This discovery sheds light on the morphological and symbiotic adaptations of catenulid flatworms in coral reef ecosystems.

Dirks, U., Gruber-Vodicka, H. R., Leisch, N., Sterrer, W., & Ott, J. A. (2011). A new species of symbiotic flatworms,Paracatenulagalateiasp. nov. (Platyhelminthes: Catenulida: Retronectidae) from Belize (Central America). Marine Biology Research, 7(8), 769–777. https://doi.org/10.1080/17451000.2011.574880