Arctic Sea Ice Nematodes (Monhysteroidea), With Descriptions of Cryonema Crassum Gen. N., Sp. N. and C. Tenue Sp. N

Abstract

Arctic sea ice presents a habitat to nematodes living in the lacunary system close to the undersurface of the ice. Only members of the Monhysteroidea have been encountered as yet, and it appears that these nematode species are confined to the ice habitat. In collections from the Fram Strait, near Greenland, and the Laptev Sea, off Siberia, we rediscovered Theristus melnikovi Tchesunov, 1986, previously described from the Central Arctic Ocean. Cryonema crassum gen. n., sp. n. and Cryonema tenue sp. n. were collected off Siberia; juveniles of Cryonema spp. have also been found in the Fram Strait. The new genus Cryonema is closely related to the genus Gammarinema and to similar genera which occur in association with crustaceans, e.g. in the gill chambers of land crabs, and to Odontobius ceti, an inhabitant of the baleen of whales. The tail tip of Cryonema contains an internal funnel-like structure, possibly part of a closure mechanism for the caudal glands; similar structures have been observed in some other related genera. Many ice nematodes show an empty intestine; sometimes single protist cells or granular substances were observed. Cryonema crassum may feed on small nematodes.

Abundance, biomass, composition and grazing impact of the sea-ice meiofauna in the North Water, northern Baffin Bay

“…This species accounted for 90% of the total abundance of nematodes and was only represented by juveniles. The other 2 species were Cryonema tenue Tchesunov &Riemann 1995, andTheristus melnikovi Tchesunov 1986. For each species, only 1 adult individual (female) per each species was found, the remaining individuals being juveniles.…”

“…Given that our land fastice station is representative of the coastal fast-ice in the North Water, the coastal sea-ice meiofaunal community composition in the North Water would appear to be similar to other arctic areas. All nematodes found at the land fast-ice station belonged to the superfamily Monhysteroidea, for whom representatives are described as living in extreme habitats (Tchesunov & Riemann 1995). Until now, the most abundant species identified as Monhysterid sp.…”

“…However, we did not observe any trace of sediments within the ice, suggesting that benthic animals were not incorporated in the land fast-ice through sediment resuspension. Other processes that have been proposed to explain the occurrence of nematodes in the ice include sowing of newly formed ice by pieces of multi-year ice (Tchesunov 1986), and transport by other animals such as amphipods (Tchesunov & Riemann 1995), some species of Decapoda Natantia (Steiner 1958), or whales by means of their baleen (Lorenzen 1986). These 2 hypotheses cannot be rejected, since multi-year ice is observed in the North Water and transport by animals is unknown.…”

“…Despite the abundance of diatoms in the land fast-ice, there was no clear indication for this food uptake by nematodes. Tchesunov & Riemann (1995) suggested dissolved organic matter as a possible contributor to the nutrition of nematodes. Recently, Moens et al (1999) demonstrated that adoncholaimid nematodes were able to feed on dissolved organic matter.…”

Arctic Marine Biodiversity: An Update of Species Richness and Examples of Biodiversity Change

“…The inventory remains incomplete due to the need for live identification of several dominant sea ice taxa, such as rotifers and acoel flatworms, and the concurrent lack of taxonomists working on those groups in the Arctic. Recently described iceendemic species include the first known sympagic hydroid, Sympagohydra tuuli (Piraino et al, 2008) and one of the few, but very abundant, sympagic nematode species, Cryonema tenue (Tchesunov and Riemann, 1995). Sea ice endemic species also include several prominent amphipods (Table 1).…”