A new mudworm: Polydora lingshuiensis

Mud worms are small, segmented, burrowing, tube-building worms. Often forming large colonies, they can smother other benthic invertebrates in the area. They usually collect bits of sediment and mud and excrete the mud after separating out the food. This mud will build up around the worms, creating a thick layer of sediment around the worm colony. In areas heavily populated with mud worms, over 40 worms can be present per square centimeter. This can have a significant impact on oyster beds, as they can be completely buried in sediment accumulated by these worms. Burial can be deadly to the oysters, leading to suffocation of the bed. Mud worms have been found in large numbers thriving in areas that have considerable oil pollution. They are very tolerant of pollution and will continue to grow and reproduce even in the presence of oil.

Some species of the genus Polydora, such as our new species, can also live in hard calcareous materials, such as corals, coralline algae, and mollusk shells. These shell-boring species can bore into the shells of abalones, oysters, mussels, and scallops to build a large number and a wide variety of burrows inside the shells. Polydora lingshuiensis is such a shell-boring species and was found in mudtubes on the surface of oyster shells but also from burrows in the inner shell surface. The scientists named them in reference to the Lingshui County, Hainan Province, China where they found the new species.

Abstract: A new polydorin species, Polydora lingshuiensis sp. n., which is found not only in burrows of pearl oyster shells (shellboring type) but also in mudtubes on the surface of pearl oyster cages (tube-dwelling type), is described with the use of light microscopy, scanning electron microscopy, and molecular phylogeny. Morphological and molecular distinctions between P. lingshuiensis and other related species reveal that P. lingshuiensis is a valid new species. The reproduction characteristic that the eggs of P. lingshuiensis are gathered together in one hollow cylinder is another piece of evidence confirming that it is indeed a valid new species. Sequence comparisons based on nuclear 18S rDNA, 28S rDNA, and mitochondrial 16S rDNA show that strains of the shell-boring type possess as high as 99.9% to 100% sequence identity relative to those of the tube-dwelling type. This finding evidently indicates that these species types are conspecific. We also find that a comparison of mitochondrial 16S rDNA sequences can provide a higher resolution of polydorin species than those of the nuclear 18S rDNA because the former has a higher interspecific/intraspecific difference ratio. Phylogenetic analyses based on 18S rDNA sequences indicate that all P. lingshuiensis samples group together to forming a sister clade to Polydora uncinata and thus fall within Polydora aura/P. uncinata clade.