Half-banded Roundhead

About this species

Fiona pinnata, common name Fiona, is a species of small pelagic nudibranch, a marine gastropod mollusk in the superfamily Fionoidea. This nudibranch species lives worldwide on floating objects on seas, and feeds mainly on barnacles, specifically goose barnacles in the genus Lepas.

Text from the Wikipedia article “Fiona pinnata”, licensed CC BY-SA 4.0. Read the article

Where and when

Where it has been recorded

Worldwide

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Best months

Worldwide (open data)

January: 74 records
February: 26 records
March: 65 records
April: 30 records
May: 52 records
June: 49 records
July: 29 records
August: 33 records
September: 21 records
October: 24 records
November: 95 records
December: 24 records

Depth and water temperature

Depth

Mostly recorded at 0–16 m · Deepest record: 663 m

0–10 m: 11 records
10–20 m: 2 records
20–30 m: 0 records
30–40 m: 0 records
40–50 m: 0 records
50–60 m: 0 records
60–70 m: 0 records
70–80 m: 0 records
80–90 m: 0 records
90–100 m: 0 records
100–110 m: 0 records
110+ m: 1 records

Water temperature

Recorded in surface water of 8–29 °C

6–8 °C: 1 records
8–10 °C: 1 records
10–12 °C: 97 records
12–14 °C: 15 records
14–16 °C: 37 records
16–18 °C: 12 records
18–20 °C: 4 records
20–22 °C: 13 records
22–24 °C: 21 records
24–26 °C: 13 records
26–28 °C: 6 records
28–30 °C: 5 records

Photos

(c) Javier, some rights reserved (CC BY) · CC BY · iNaturalist
(c) Luca Davenport-Thomas, some rights reserved (CC BY) · CC BY · iNaturalist
(c) Luca Davenport-Thomas, some rights reserved (CC BY) · CC BY · iNaturalist
(c) Saryu Mae 前朝琉, some rights reserved (CC BY) · CC BY · iNaturalist
(c) Eric Klug, some rights reserved (CC BY) · CC BY · iNaturalist
(c) Acacia, some rights reserved (CC BY) · CC BY · iNaturalist
(c) tunicatedreamz, some rights reserved (CC BY) · CC BY · iNaturalist

Names and classification

English: Half-banded Roundhead, Feather Aeolid, Fiona, Pelagic Nudibranch

Names in 3 more languages

French: Fiona pennée
Japanese: ヒダミノウミウシ
Korean: 주름도롱이갯민숭이

Other scientific names: Aeolis plicata, Cavolina natans, Dolicheolis longicauda, Doris fasciculata, Eolidia longicauda, Eolidia natans, Eolidia pinnata, Fiona atlantica, Fiona marina, Hymenaeolis elegantissima, Limax marinus, Oithona nobilis

Similar species

Sources and credits

Names and taxonomy: WoRMS (CC BY 4.0) and the GBIF Backbone (CC BY 4.0). Photos: iNaturalist observers, each under the licence shown (CC0, CC BY or CC BY-SA).

Depth, temperature, months and maps: records from OBIS and GBIF under CC0 or CC BY.
Descriptions: Wikipedia, licensed CC BY-SA, each linked to its article.
Conservation status as published by GBIF (IUCN Red List).
338 open-data records from 1881 to 2026.
Species data updated November 2, 2026.