Learn Finnish: Matalikolta on löydetty harvinaisia eläimiä, kuten tämä simpukka. - Rare animals, such as this clam, have been found in the shallows.

When using kuten (such as / like) to introduce a specific example, the noun following it is very often put in the nominative case, even if the broader category it refers back to is in another case. You are essentially just naming the item: 'such as (this thing): this clam'. While matching the case (e.g., kuten tällaista simpukkaa) is also grammatically possible, using the nominative is very natural and common when pointing out a distinct, standalone entity.

How is the noun matalikko (shallows) formed?

It is built from the adjective matala (shallow or low). The suffix -ikko or -ykkö is used to create nouns that describe a specific place, terrain, or a cluster of things characterized by the root word. So, matalikko literally means a 'shallow place' or 'shallows'.

Why do we use the ablative case (-lta) meaning 'from' the shallows, instead of 'in' the shallows?

In Finnish, the verb löytää (to find) is a directional verb. You do not find something in a location; you find it from a location. Because a shallow area is conceptualized as an open space or surface, it takes the external 'from' case, which is the ablative (-lta), rather than the internal elative case (-sta).

What is the grammar structure behind on löydetty?