New crustacean species found in Galicia

A group of scientists from the University of Vigo and the Australian Museum have found a new species of crustacean endemic to Galicia in the inlet of O Grove (Pontevedra) and have named it Uromunna naherba. It belongs to the Isopod order (Peracarida suborder), the most diverse of the crustaceans.

"In Galician we call it na herba ('on the grass' in English) because we find it on the marine phanerogams, otherwise known as eelgrass beds," explains Patricia Esquete, co-author of the study at the University of Vigo and currently working for the University of Aveiro (Portugal).

These peracarida are found in all types of environment, especially marine ones, although there are also land and freshwater species. Uromunna naherba measures between 0.6 mm and 1.5 mm in length and lives between the leaves and in the rhizomes (underground stems), although the females carrying eggs tend to live in the latter.

"Uromunna naherba does not have fins with which to swim or stay suspended in the water to be taken by the current, so it does not cover great distances. Only the adults of this species are able to swim, although rarely far," explains the researcher.

One peculiarity of the peracarida in general, and of isopods in particular, is that no stage of their life cycle has a dispersive function. This means that at no point does the animal cover large distances, whether to colonise new habitats or to find new substratum. Therefore, it is a species that does not swim, but walks along the bottom of the sea on both algae and plants.

All of this, added to it being a small species with limited movements means that it is prone to speciation and endemism regularly occurs. "In fact the constant evolution of the peracarida means that numerous new species may appear," says Esquete.

"As they cannot move far in a short space of time, the individuals of the population reproduce amongst themselves, without there being any cross with other populations," adds the expert. "Therefore, the genetic mutations are spread rapidly within the populations but do not extend to populations further away." Thus, over time, the population will have accumulated so many mutations differentiating it from others that it becomes a new species.

Good weather, more reproduction

Uromunna naherba reproduces all year round. However, scientists observed that the egg-carrying females are more common at the end of spring and in summer. This fact coincides with the moment of plants' annual cycle when their leaves and rhizomes are at their greatest, and more substratum and food are available.

According to the researcher, there is a lack of information on the natural history of the peracarida because they are not edible, and therefore are of no commercial interest. The new species was found in the seagrass beds in densities of up to 900 individuals per square metre in some cases.

"We were not really looking for new species. They normally appear when taking samples for an ecological study," Esquete points out.

Another new species between Spain and Portugal

The research team also found another species in the samples collated. It is a specimen of the Apseudopsis genus which is difficult to identify because it is very similar to the species already discovered.

"It was a surprise, because it is a very common and abundant genus on the European coasts. It is considered that the fauna of these coasts are very well known, but we are seeing that this is not the case. In fact, it is that statement that generates confusion and incorrect identifications, and stops progress," says the scientist.

The new species, a peracarid known as Apseudopsis adami (Tanaidacea order), measures between 4.5 mm and 5 mm as an adult. Unlike Unamunna naherba, it is not native to Galicia and has been found along the coast up to the Algarve, in the south of Portugal.

"It had simply gone unnoticed due to its similarity to the only species of the genus present in this area," concludes Esquete.