Comparative descriptions of non-adult stages of four genera of Gordiids (Phylum: Nematomorpha)

Abstract

Freshwater hairworms infect terrestrial arthropods as larvae but are free-living in aquatic habitats as adults. Estimates suggest that only 18% of hairworm species have been described globally and biodiversity studies on this group have been hindered by unreliable ways of collecting adult free living worms over large geographical areas. However, recent work indicates that non-adult cyst stages of hairworms may be the most commonly encountered stages of gordiids in the environment, and can be used for discovering the hidden diversity of this group. Unfortunately, little information is available on the morphological characteristics of non-adult stages of hairworms. To address this problem, we describe and compare morphological characteristics of non-adult stages for nine species of African and North American gordiids from four genera (Chordodes, Gordius, Paragordius, and Neochordodes). Observations were made on the oviposition behavior of adult worms and morphological characteristics were recorded for egg strings, larvae and cysts using light and differential interference contrast microscopy and/or scanning electron microscopy. Our study indicates that three distinct types of oviposition behaviors and three distinct morphological types of egg string, larva, and cysts were present among the four genera of gordiids. Although species identification based on cyst characteristics was not always possible among different species of gordiids, cyst morphology was conserved among some genera and all clades of gordiids. More importantly, our work indicates that gordiid larval morphology can be used for predicting cyst morphology among other gordiid genera. The capability to identify and predict gordiid genera and/or clades based on cyst morphology will be useful for culturing gordiids in the laboratory from field collected cysts and these new techniques will undoubtedly allow others to discover new species of gordiids from around the world.

Annual Survey of Horsehair Worm Cysts in Northern Taiwan, with Notes on a Single Seasonal Infection Peak in Chironomid Larvae (Diptera: Chironomidae)

“…1). The morphology was similar to that of the larval Gordius described by Hanelt and Janovy (2002) and Szmygiel et al (2014) but with a considerably shorter body. None of these cysts had surrounding cyst walls; approximately half of these individuals were dark in color and appeared to be attacked by host immune responses.…”

“…The definitive host range of horsehair worm cysts is narrow; however, the cysts are found in a wide range of animals, including vertebrates and invertebrates (Schmidt-Rhaesa and Ehrmann, 2001;Schmidt-Rhaesa, 2013). Although the morphology of the cysts is not as well described as that of the adult stage (Szmygiel et al, 2014), it has been recently applied as an indicator for estimating their geographic distribution (Hanelt et al, 2001) and species composition (Bolek et al, 2013b). In the terrapintrematode system, the metacercarial cysts of the trematode have been used to estimate the abundance of terrapins (Byers et al, 2010).…”

Using Gordiid cysts to discover the hidden diversity, potential distribution, <br />and new species of Gordiids (Phylum Nematomorpha)

“…Additionally, digital photographs were taken for at least 20 cysts/larvae per infected snail for snails with higher intensities than 20 cysts and/or larvae. The folding pattern of larvae within all fully formed cysts and the size of unencysted larvae in each snail were compared to morphological characteristics provided in Szmygiel et al (2014). Briefly, cysts were grouped into three categories: folded once with small visible spines on the preseptum (species in the genera Chordodes Creplin, 1847 andNeochordodes Carvalho, 1942), folded twice with distinct large spines on the preseptum (species in the genus Paragordius Camerano, 1897), or folded twice without spines on the preseptum (species in the genus Gordius Linné, 1758).…”

“…or Gordius spp. based on length measurements of the preseptum and postseptum and the presence or absence of long outer hooks on the outer ring of the preseptum and then compared to measurements and morphological characteristics for larvae of gordiids reported in Szmygiel et al (2014). Prevalence, the mean intensity (MI) and range, and mean abundance ± 1 standard deviation (MA ± 1 SD) were calculated for each location sampled according to Bush et al (1997).…”

“…While traditionally adults are needed for species identification, our work on non-adult stages of gordiids indicated that the folding pattern of the encysted larvae can be used in generic and/or clade identification of gordiid cysts (Szmygiel et al 2014). Using this information, Hanelt et al (2012) and Bolek et al (2013a) collected snails infected with two types of gordiid cysts from Kenya, a country for which no gordiid records existed.…”