Abstract
Freshwater hairworms (class Gordiida) are members of the phylum Nematomorpha that use terrestrial arthropods as definitive hosts but reside as free-living adult worms in rivers, lakes, or streams. The genus Gordius consists of 90 described species, of which three species were described from freshwater habitats in North America. In this paper we describe a new species of Gordius from terrestrial habitats in Oklahoma, Texas, and Louisiana, United States. Oddly, each year hundreds of adult free-living worms appear after bouts of heavy rain on streets, sidewalks, and lawns during the winter season, when terrestrial arthropod hosts are not active. The new species is described based on morphological characters of adults and non-adult stages including the egg strings, eggs, larvae, and cysts. Adult males have a unique row of bristles on the ventral inner side of each tail lobe and a circular pattern of bristles on the terminal end of each lobe, which distinguishes them from all other described North American species of Gordius. The egg string, larval, and cyst morphology of this new species conform to previous descriptions of non-adult hairworm stages for the genus Gordius. However, the eggs of this new species of hairworm are unique, as they contain an outer shell separated by distinct space from a thick inner membrane. The consistent occurrence of this gordiid in terrestrial habitats, along with its distinct egg morphology, suggests that this new species of hairworm has a terrestrial life cycle.
Highlights
The Phylum Nematomorpha, commonly known as hairworms or Gordian worms, or gordiids, are parasites of terrestrial arthropods with a complex life cycle that includes a free-living and parasitic phase with multiple hosts (Carvalho 1942; Townsend 1970; Blair 1983; Poinar and Brockerhoff 2001; Hanelt et al 2005)
Gordius terrestris sp. nov. represents the first hairworm species consistently collected from a terrestrial habitat
Hundreds of adult free-living worms appeared after bouts of heavy rain on streets, sidewalks, and lawns during the winter season, where male and female worms were observed mating and some females were observed depositing egg strings
Summary
The Phylum Nematomorpha, commonly known as hairworms or Gordian worms, or gordiids, are parasites of terrestrial arthropods with a complex life cycle that includes a free-living and parasitic phase with multiple hosts (Carvalho 1942; Townsend 1970; Blair 1983; Poinar and Brockerhoff 2001; Hanelt et al 2005). It is hypothesized that only 18% of the estimated 2000 gordiid species have been described (Bolek et al 2015) Because of their life cycle that includes an aquatic environment where worms emerge as free-living adults from their arthropod host, sampling for hairworms and discovering their true biodiversity has been challenging (Hanelt et al 2005). Based on morphological characteristics of non-adult stages, and the occurrence of adult free-living worms of this new species in terrestrial habitats, we provide evidence and suggest that this new species of gordiid has a terrestrial life cycle
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