Description: The main stems arise from a basal stolon, and are zig-zag shaped. The main stem is usually unbranched and annulated in the basal region and between each hydrotheca. The hydrothecae are alternate and more widely spaced than in Sertularella rugosa. They are barrel shaped with transverse annulations, the aperture is approximately square shaped, and has a single denticle at each corner. The operculum consists of four flaps. The gonothecae are oval shaped with transverse ridges. The aperture is slightly raised with 3-4 denticles.

Habitat: This species often grows attached to other hydroids.

Distribution: Recorded from all around the British Isles.

Similar Species: The main stems are shorter and finer than those of Sertularella rugosa, and the annulations on the hydrothecae are less well-developed but more numerous than in that species.

Key Identification Features:

• Unbranched main stems
• Hydrothecae with annulations

Distribution Map from NBN: Sertularella tenella at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Sertularella tenella at iNaturalist World Species Observations database.

WoRMS: Sertularella tenella at World Register of Marine Species. Accepted name: Sertularella tenella (Alder, 1857). AphiaID: 117909.

Classification: Biota; Animalia; Cnidaria; Medusozoa; Hydrozoa; Hydroidolina; Leptothecata; Sertularioidea; Sertularellidae; Sertularella