Mariella is an ammonoid genus, named by Nowak (1916) from the upper Albian and Cenomanian stages of the mid Cretaceous, included in the Turrilitidae.

The shell is asymmetric, closely wound in a long expanding trochoidal spire.

Ribs are slightly oblique and are rather feeble, each with 4 more or less equally spaced tubercles.

Turrilites differs primarily in being more strongly ribbed and in having a more oval aperture.

Fossils of Mariella have been found in Angola, Antarctica, Australia, Brazil, Canada (British Columbia), Colombia (Hiló Formation), France, Germany, Iran, Japan, Kazakhstan, Madagascar, Mexico, Mozambique, New Zealand, South Africa, Spain, Switzerland, Turkmenistan, Ukraine, the United Kingdom, and the United States (California, Texas, Oregon).