Anatomical, histological, and ultrastructural investigation of the hydrothermal vent phyllodocid Galapagomystides
aristata shows that this unusual polychaete has a normal mouth and
foregut but a highly modified
midgut with a
blood-filled
lumen. The foregut includes a protrusible proboscis armed distally with minute spines. Midgut
tissues contain concentrically banded spherocrystals, composed mainly of iron, phosphorus, and silicon, and abundant lipid droplets. The blood-filled midgut lumen extends to the final segment of the worm, but we find no sign of an anus. There is no evidence of symbiotic bacteria in tissues of G. aristata. Stable isotope analyses indicate that G. aristata is likely to be a secondary consumer. We propose that these worms are hematophagous, although they lack many common
Anatomical adaptations for a blood-sucking way of life.