Nature Today |  The worm from the delta region is new to science

Nature Today | The worm from the delta region is new to science

During various studies carried out in the waters of the Dutch delta, a gill nematode was observed that was not immediately reminiscent of an already known species. Although this animal resembles a species from the Mediterranean, it turns out to be a different worm, which has not yet been described. Worldwide, there were 13 known species of this genus protocerinres. Now comes 14H In, described based on materials from our country. Researchers Ton van Haaren and Marco Lisi used animals from the Oosterschelde, Grevelingen and Verse Meer in the scientific description.

Searching in Dutch waters

Research is regularly carried out on behalf of the Rijkswaterstaat in its formation Benthic Communities in different national waters. In addition to the North Sea, this also concerns Grevelingenmeer, Verse Meer, Oosterschelde and Westerschelde. With the help of A Van Weinhaber to Pulp box A bite is taken from the bottom of the vessel. The contents are rinsed on deck over a sieve and the material left behind is preserved and sorted in the laboratory where the animals present are identified (named). These faunas can consist of all kinds of animal groups, including brittle stars, bivalves, crustaceans, and worms.

Worms with threads

One of the largest groups of marine worms (that live in salt water) is the family Cirratulidae, or “gill nematodes.” There are currently 394 species known worldwide, divided into 16 different genera. It is not always easy to distinguish between different genera and species. What almost all of them have in common is the presence of a large number of tentacles (cirri) on top of their bodies. There are at least 13 species of gill nematodes known in the Netherlands, belonging to 8 different genera. A famous representative in the Netherlands is the red gill worm (Al-Hadiya Al-Makhsiyya), a species with strikingly long red gill filaments that protrude above the bottom. This worm, which is now no longer rare in the Oosterschelde, has been discussed before in the Nature Report.

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to get to know

The newly discovered species has shorter and smaller gill filaments. Marco Lisi and Ton van Haaren described this species in a scientific article recently published in Taxonomy (MDPI). They gave the animal its scientific name Primary storms, for which the species is named after Amy Storm, former leader of the AquaSense team (Amsterdam) and Ton's colleague for over twenty years. This is a relatively small species about four to seven millimeters long and about half a millimeter in diameter (based on preserved material). The animal is characterized, among other things, by a sharp head, flat belly and brown color. There is another type of gill nematode in the Netherlands, which is brown in color and has a blunt head (Twelve shells), but the abdomen is less flat and the hairs on the tail are uniquely sharp. The flatgill worm has hairs all over its body, but unlike many other gill worms, there are no other abnormally shaped hairs. This makes the animal almost immediately distinguishable from other gillworms.

Flat belly

Precisely because of the sharp head, flat abdomen, and presence of only hair, it soon became clear to the authors what gender they should be looking for (protocerinres), although it initially remained unclear whether the worm did not belong to one of the other thirteen species in the genus. It appears that this is not the case. The flat stomach also gave rise to a distinctive Dutch name. It is proposed that the new species will henceforth be called Gillworm flatworm.

It is forbidden

The flat gill nematode has been present in the Dutch Delta since at least 2013. The first official observation comes from Grevelingenmeer, where the species was collected on 27 March 2013. Not long after, specimens were also found in the Oosterschelde (16 September 2013). Research in 2016, 2020 and 2021 only revealed how common this species is in the Delta. A total of 108 observations (between 2013 and 2021) from Grevelingenmeer, Verse Meer and Oosterschelde are currently known. This species is found there at depths ranging from 0.8 to 44 metres. Density can reach more than 12,000 individuals per square meter. These high densities are achieved in both Oosterschelde and Grevelingenmeer. The density in Veerse Meer is only 846 individuals per square meter. It is striking that the number of observations is particularly high in Grevelingenmeer. This species is very common here and throughout the lake. In the Oosterschelde and Verse Meer, observations are only known from the eastern part. No specimens have been found in the West Scheldt. Flat-gill nematodes seem to prefer places with reasonably stable salinity and high transparency. The animals can tolerate lower levels of oxygen and greater differences in water temperature in summer and winter. The West Scheldt is a truly open estuary with a fresh water supply from the Scheldt and therefore greater fluctuations in salinity. Therefore this habitat may be less suitable for this species.

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Places where gill flatworms have been found are Oosterschelde, Grevelingenmeer and Verse Meer.  Positive observations are indicated by a larger black dot.  A search was conducted in the places marked with a small gray dot, but the species was not found

Brought, exotic or never recognized?

The fact that the new gill nematode was only observed for the first time in 2013 gives the impression that it is not a native Dutch species in origin, but, for example, an imported exotic species. Research on gill worms from the delta region of the Naturalis group in the period from 1941 to 1977 showed that there are no worms with flat gill threads among them. So you might assume so Primary storms It was introduced at some point, at least ten years ago. But because this group of worms is difficult to identify and because identification keys used in the past led to other species and genera, it is not unlikely that they actually existed in the past but were incorrectly identified. On the other hand, it is not unlikely that this species is native and was almost never found here before the delta works, because the habitat was less suitable at that time. Since the 1960s, much has changed in the exchange with the sea in the delta area. Grevelingen (1971) and Oosterschelde (1986) were closed and the Veerse Meer was closed in 1961 and reconnected to the Oosterschelde in 2004. Perhaps there was simply less suitable habitat for this worm at that time.

New Dutchman

Discovering a new species in our country is always exciting. These usually concern species that have been known to science for a long time, but have recently become established among us. Or it concerns species that were discovered or recognized for the first time. Entirely new species in science are much more than just exciting. The fact that a species is described based on Dutch material and also named after a Dutch person is not only interesting but also unique. We can be proud of that!

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more information

Text: Ton van Haaren and Rykiel de Bruyne, Anemon Foundation.
Image: Ton van Haaren (Main image: The flat gill worm newly described to science Primary storms (preserved specimen with most of its claws broken)); Marco Lisi

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