In Aragon without sea but with a variety of rivers, canals, streams, etc. in various states of conservation, there are still various species of bivalve mollusks, included in the National Catalog of Endangered Species, known as naiads or freshwater clams.
The name naiads is used in honor of the mythical nymphs, protective beings of rivers and streams, who guarded the water currents.
Their way of life filtering and purifying water, and therefore causing a benefit to those who later use it, makes them worthy of this name.
Freshwater clams constitute a very large family, whose species all have great similarity to each other.
In Aragon there are four different species of naiads.
Anodonta cygnea
The most abundant and visible (it is the largest) is the Anodonta cygnea. It is the least demanding species and can be found in the depths silt from canals, reservoirs and slow sections of rivers. Adults reach large sizes, up to twenty centimeters.
Its shell is characterized by being very domed, by the brownish exterior color and by not having noticeable teeth in the hinge (an-odonta = without teeth).
The valves of this naiad are very thin and when they are exposed out of the water they quickly dry out and crack.
Potomida littoralis
In the Potomida littoralis species, adults reach up to 9 centimeters.
Its shell is solid, slightly sinuous on the edge and in the meat the teeth are well developed.
Externally it is blackish brown in color. This naiad needs cleaner waters than Anodonta.
Unio elongatulus
It also has teeth in the hinge.
The shells of adults reach 12 centimeters and have an elongated shape.
Externally it is greenish yellow or brownish yellow.
It also requires water of a certain quality.
Live specimens of Anodonta cygnea (top center), Potomida littoralis (bottom left)
and Unio elongatulus (bottom right).
[Author: Ramón M. Álvarez Halcón, 1999].
Margaritifera auricularia
It is the rarest species.
It has an extremely thick and heavy shell, blackish in color, with a curved appearance, like a human ear (auricula = ear).
It reaches 20 centimeters in length.
It lives in gravel and sandy bottoms, and also needs water of a certain quality and channels in good condition.
While the first three species of naiads are relatively abundant, and are found in much of the Iberian Peninsula and Europe, Margaritifera auricularia is only found in the Ebro valley in the entire world.
Specifically, malacologists are only aware of the presence of this species in the provinces of Zaragoza and Tarragona.
In Zaragoza there are known colonies in the Imperial Canal (where about two thousand specimens have been recorded).
In the Tauste Canal and in the area of Sástago in the Ebro River, unquantified.
In Tarragona there are known colonies in the final stretch of the Ebro.
For scientists at the National Museum who have been studying the specimens of the Imperial Canal since the mid-90s, most of the known individuals of the species live in a small stretch of this canal in Zaragoza.
This means that we Aragonese have the privilege of hosting a unique and scarce species but also a great responsibility in the conservation of this naiad.
Image of a live specimen of Margaritifera auricularia from the Tauste Channel.
© Photo: Ramón M. Álvarez Halcón Archive (2001).
The larvae of these mollusks have the curious peculiarity of living for some time tightly attached to the gills or fins of the fish that swim through their waters. When they have acquired the necessary development, they break off and end their lives crawling through the mud of the bed.
The shells of bivalves are made of calcium carbonate, and as they are pearly on the inside, they were used until a few years ago for the manufacture of buttons and knife handles.
In the species Margaritifera margaritifera, which lives in the northern regions of Spain, it is common for pearls to form spontaneously or induced, (hence the name Margariti-fera: who makes pearls). In the related Aragonese species Margaritifera auricularia this is very rare and unusual.
Like freshwater clams, many mollusks are excavators, but their job is very simple, and consists of introducing the animal into the mud or rocks at the bottom, to hide from their enemies.
The body of all mollusks that have this habit is more or less elongated, so that they can reach the water for food purposes while the shell remains buried.
Other information about Molluscs
- Introduction
- Monoplacophores
- Poliplacophores
- Scaphopods
- Gastropods
- Bivalves or lamelibranchs
- Cephalopods
Other information about fauna in Aragón:
A small list of species in Aragon would be the following:
| Vertebrates | Invertebrates |
|---|---|
MammalsBirdsReptilesAmphibiansFishes |
MetazoansProtozoa |
|
images about the fauna in Aragon. photographs on invertebrates. beneficial animals for agriculture. | |
Also Aragon enjoys a diverse and varied Nature where passing by plants, animals, Geology, or landscapes we can arrive at a fantastic bestiary that lives in its monuments.
The information will not be complete without a stroll by its three provinces, with shutdown in some of its spectacular landscapes like Ordesa, the Moncayo, Monegros or by opposition the Ebro.
Also you can dedicarte to the intangible ones: from the legend compilation that also does to universal Aragon.