Description of a new valvatoid Pikasia smenensis n. gen. n. sp. (Gastropoda, Hydrobiidae) from Morocco

Description of a new valvatoid Pikasia smenensis n. gen. n. sp. (Gastropoda, Hydrobiidae) from Morocco. Recent field surveys conducted in the northern part of Morocco have led to the discovery of a new species belonging to a new genus Pikasia n. gen. described here. Photos of the holotype and paratype are presented in addition to the penis morphology and the female sex tract, the map of the sampling area with the type localities, and the habitat description.


Introduction
Surrounded by the Mediterranean Sea, the Atlantic Ocean and the Sahara Desert, Morocco is one of the most interesting biogeographical regions in the occidental. Mediterranean Basin, representing a contact area between Europe and Africa and between the Palaearctic and Afrotropical region. The country has multiple geographical barriers, such as the Moulouya River Basin, the Sahara, the Rif Mountains and the Atlas Mountains. The latter divide the northern part of the country into two bioclimatic regions, which in turn are associated with high levels of endemism in freshwater fauna (Mabrouki et al., 2019;Taybi et al., 2020), giving the area a privileged place for taxonomical and ecological studies.
The truncatelloidean family Hydrobiidae Stimpson 1865 is a major group of freshwater molluscs and supposedly the largest gastropod family in Morocco. Knowledge of this family continually improving, and many new species have recently been discovered (Taybi et al., 2017;Boulaassafer et al., 2018Boulaassafer et al., , 2020Ghamizi, 2020;Glöer et al., 2020aGlöer et al., , 2020bMabrouki et al., 2020Mabrouki et al., , 2021aMabrouki et al., , 2021b. The valvatiform hydrobiid is a group of minute gastropods with depressed trochiform shells resembling those of the genus Valvata O. F. Müller, 1773. Owing to their limited dispersal abilities and high degree of habitat specialization, most springsnails are narrow-range endemics and face a high risk of extinction (Delicado et al., 2019;Radea et al., 2021). To date, five valvatoid species are known to occur in Morocco, four crenobiotic species that are micro-endemic to their type localities, namely Ifrania zerroukansis Glöer, Mabrouki and Taybi, 2020, Fessia aouintii Glöer, Mabrouki and Taybi, 2020, Islamia tiferitensis Glöer, Mabrouki and Taybi, 2020 and I. karawiyiensis Mabrouki, Glöer and Taybi, 2021, and the stygobiont Rifiya yakoubii Ghamizi, 2020 inhabits the phreatic waters of the southern border of the Rif region, upstream of Moulouya, Sebou and Loukkos basins. New research conducted recently in northwestern Morocco revealed a new valvatoid genus. The aim of this paper is to describe a new springsnail genus and species.

Description
Valvatoid shell with 3.5 slightly convex whorls and a prominent body whorl ( fig. 1, 2). The spire low and conical, diameter of the whorls fast and regularly increasing. Aperture roundish from frontal view and touches in some specimens the body whorl over a short distance or is detached from the shell wall. From lateral view the border of the aperture appears clearly inclined (fig. 3). The diameter of the body whorl near the aperture about 2.5 times broader than the umbilicus. Operculum dark yellowish. Dimensions: shell height 0.97-1.0 mm, shell width: 1.0-1.1 mm.

Animal
Eyes present, head and mantle blackish, pigmented, as were parts of the tentacles.

Penis
In its relaxed state the simple penis broad and elon-

Differentiated characters
The shells are a little similar to Aretiana wolfi (Boeters and Glöer, 2007) from S-Spain but A. wolfi is much larger (1.6-1.8 mm in diameter), and the penis in A. wolfi is smaller and hook shaped (Delicado et al., 2021). In addition, A. wolfi has a receptaculum, Pikasia smenensis has not.

Etymology
The genus name Pikasia n. gen. is given in honor of the late father of the first author (El Pikas). The specific name refers to one of the type localities Ain Smen.

Habitat
The species occurs in rheocrenous springs only, in the upper part of Ain Chkef catchment area (a tributary of Sebou River). The grain size of the bottom consists of stones, pebbles and sand, the banks are covered with dense vegetation (fig. 7). The entire area is under anthropogenic impact.

Distribution
Morocco; only known from type localities.