common freshwater nerite vs common sea hare

Theodoxus fluviatilis compared with Aplysia punctata

Taxonomic Classification

Rank	common freshwater nerite	common sea hare
Kingdom same	Animalia (Animals)	Animalia (Animals)
Phylum same	Mollusca (Mollusks)	Mollusca (Mollusks)
Class same	Gastropoda (Gastropoda)	Gastropoda (Gastropoda)
Order	Cycloneritida (Cycloneritida)	Aplysiida (Aplysiida)
Family	Neritidae	Aplysiidae
Genus	Theodoxus	Aplysia
Species	Theodoxus fluviatilis	Aplysia punctata

Evolutionary Relationship

common freshwater nerite and common sea hare share a common ancestor at the Class level: Gastropoda. (Gastropoda)

Conservation Status

common freshwater nerite

LC — Least Concern

common sea hare

LC — Least Concern

Physical Characteristics

Attribute	common freshwater nerite	common sea hare
Diet	—	—
Average Lifespan	—	—
Average Length	—	—
Average Weight	—	—

Habitat & Geographic Range

common freshwater nerite

Habitat

Typically found in terrestrial and aquatic habitats including forests and freshwater.

Range

Found across Europe (11 countries).

common sea hare

Habitat

Typically found in terrestrial and aquatic habitats including forests and freshwater.

Range

Distributed across Denmark, Norway, Portugal, and Sweden.

common freshwater nerite

<em>Theodoxus fluviatilis</em>, commonly known as the common freshwater nerite, is a small aquatic gastropod mollusc belonging to the family Neritidae. This species is widely distributed across Europe, with documented occurrences in Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Hungary, Latvia, Norway, and Sweden. It typically inhabits freshwater environments, including rivers, streams, and lakes, where it grazes on algae and biofilm on hard substrates such as rocks and submerged wood. The common freshwater nerite is assessed as Least Concern on conservation metrics, reflecting its broad distribution and relatively stable populations across much of its European range. Biological traits of this species remain poorly documented in the scientific literature. <em>Theodoxus fluviatilis</em> plays an ecological role as a grazer in freshwater benthic communities, contributing to the regulation of algal growth on hard surfaces. The species typically favors clean, well-oxygenated waters and can serve as an indicator of water quality in freshwater systems. Its distinctive small, dome-shaped shell with variable patterning makes it recognizable among freshwater invertebrates.

common sea hare

<em>Aplysia punctata</em>, the common sea hare, is a large opisthobranch sea slug in the family Aplysiidae, order Aplysiida, found in the northeastern Atlantic Ocean and Mediterranean Sea, with confirmed records from Denmark, Norway, Portugal, and Sweden. This species typically inhabits shallow subtidal and intertidal zones with abundant macroalgae, feeding primarily on red and green algae — a diet that influences the color of the defensive purple ink it secretes when threatened. <em>Aplysia punctata</em> is a simultaneous hermaphrodite, capable of acting as both male and female during mating, and often forms mating chains involving multiple individuals. It can reach considerable size among European opisthobranch species, though body dimensions vary considerably with age and feeding conditions. The species is classified as Least Concern by the IUCN, reflecting stable populations across its coastal range. Biological traits for this species remain poorly documented in the scientific literature, including precise average data on lifespan, body length, weight, and detailed seasonal dietary patterns, though its general herbivorous feeding on macroalgae is well established.

Shared Countries

Both species can be found in 3 countries:

🇩🇰 Denmark 🇳🇴 Norway 🇸🇪 Sweden