Coastal Silver-stiletto vs Colonial tunicate

Acrosathe annulata compared with Symplegma reptans

Key Differences

• Coastal Silver-stiletto is Least Concern while Colonial tunicate is Not Evaluated.

Taxonomic Classification

Rank	Coastal Silver-stiletto	Colonial tunicate
Kingdom same	Animalia (Animals)	Animalia (Animals)
Phylum	Arthropoda (Arthropods)	Chordata (Chordates)
Class	Insecta (Insects)	Ascidiacea (Ascidiacea)
Order	Diptera (Diptera)	Stolidobranchia (Stolidobranchia)
Family	Therevidae	Styelidae
Genus	Acrosathe	Symplegma
Species	Acrosathe annulata	Symplegma reptans

Evolutionary Relationship

Coastal Silver-stiletto and Colonial tunicate share a common ancestor at the Kingdom level: Animalia. (Animals)

Conservation Status

Coastal Silver-stiletto

LC — Least Concern

Colonial tunicate

NE — Not Evaluated

Physical Characteristics

Attribute	Coastal Silver-stiletto	Colonial tunicate
Diet	—	—
Average Lifespan	—	—
Average Length	—	—
Average Weight	—	—

Habitat & Geographic Range

Coastal Silver-stiletto

Habitat

Typically found in virtually all terrestrial and freshwater habitats.

Range

Distributed across Belgium, Denmark, Norway, and Sweden.

Colonial tunicate

Habitat

Native to Europe and North America, inhabiting ecosystems characteristic of the region.

Range

Distributed across Mexico, Norway, Sweden, and United States.

Coastal Silver-stiletto

Coastal silver stiletto (Acrosathe annulata) is a slender robber fly in the family Therevidae, native to northwestern Europe, including the United Kingdom, France, the Netherlands, Belgium, and Scandinavia. Adults are found on coastal sand dunes and sandy heathland, where they perch on bare sand to ambush small flying insects. Stiletto flies in the family Therevidae are characterised by a slender body, long pointed abdomen, and predatory habits; adults prey on a variety of small dipterans and other flying insects during warm, sunny periods. Larvae develop in sandy soil, where they are also predatory, feeding on other invertebrate larvae. Acrosathe annulata is a habitat specialist restricted to open, sandy coastal habitats with sparse vegetation—environments that have declined substantially across northwestern Europe due to dune stabilisation, recreational disturbance, and the cessation of traditional dune management. The IUCN lists it as Least Concern, though regional conservation bodies in the United Kingdom have flagged population declines. It is considered an indicator of high-quality coastal sand dune habitats and is monitored through national invertebrate surveys.

Colonial tunicate

<em>Symplegma reptans</em> is a colonial tunicate in the family Styelidae with known occurrences in Mexico, Norway, Sweden, and the United States. This species has not been evaluated by the IUCN. Colonial tunicates in the genus <em>Symplegma</em> form encrusting sheet-like colonies on hard marine substrates, including rocks, shells, and artificial structures, in shallow coastal environments. Each colony is composed of multiple filter-feeding zooids embedded in a common tunic, through which nutrients and metabolites are distributed. The presence of <em>Symplegma reptans</em> across both the North Atlantic and Pacific coastal regions suggests either a wide native distribution or a history of introduction through maritime vectors such as ballast water and hull fouling. As a sessile filter feeder, this species contributes to water column filtration and nutrient cycling within benthic communities. The reproductive biology of <em>Symplegma reptans</em> likely involves both sexual reproduction via larval dispersal and asexual proliferation through budding within established colonies. Biological traits of this species remain poorly documented in the scientific literature.

Shared Countries

Both species can be found in 2 countries:

🇳🇴 Norway 🇸🇪 Sweden