Nanomia bijuga



Conservation status

Ireland: Not considered threatened.
Europe: Not considered threatened.
Global: Not considered threatened.

Legal status

Nanomia bijuga is not afforded legal protection in Ireland.

Native status



Not assessed

Species Biology


Key identification features include:
•    Approximately 10-20 cm long when contracted, 50 cm when relaxed
•    Tentilla have a single terminal process
•    The pneumatophore is ovoid with a red pigmentation cap
•    10-20 pumping ridged bells (nectophores) arranged below for locomotion
•    Nectophores have a cube shape


Nanomia bijuga is found in oceanic and coastal habitats, and has been recorded from the surface down to a depth of 1850 m.

Source: Kirkpatrick & Pugh, 1984; Mapstone, 2015; Totton, 1965

Life cycle

Nanomia bijuga are dioecious with alternating male and female gonodendra along the stem. The life cycle is entirely planktonic. In the northeast Atlantic, adult colonies appear to reach highest abundance during June-July and small post larval colonies are also present during this time. In the Gulf of Maine and some Norwegian fjords, it has apparently established semi-resident populations surviving through winter.

Source: Haberlin et al., 2016; Mapstone, 2015; Totton, 1965

Threats faced

This species has not been assessed.


World distribution(GBIF)

Considered cosmopolitan in distribution, with records from 60°N-59°S.

Source: Mapstone, 2015; Totton, 1965

Irish distribution

Record suggest Nanomia bijuga is primarily found on the western and southern coastlines, sometime in high abundance. Distribution extends into the Celtic Sea and shelf waters and possibly into the Irish Sea.  

Source: Haberlin et al., 2016; Kirkpatrick & Pugh, 1984

Temporal change

Records submitted to Data Centre in 2021

The following map is interactive. If you would prefer to view it full screen then click here.

Further information

There are two Nanomia species, Nanomia cara and Nanomia bijuga, and both have probably been confused in many historic sightings. It is likely that many observations recorded as N. cara are in fact N. bijuga.



Haberlin, Damien, et al. "Diversity and occurrence of siphonophores in Irish coastal waters." Biology and Environment: Proceedings of the Royal Irish Academy. Vol. 116. No. 2. Royal Irish Academy, 2016.

Kirkpatrick, P. A., and P. R. Pugh. "Siphonophores and Velellids." Synopsis of the British Fauna (New Series) no. 29 (1984): 154.

Mapstone, Gillian. "Correction: global diversity and review of Siphonophorae (Cnidaria: Hydrozoa)." PloS one 10.2 (2015): e0118381.

Totton, Arthur Knyvett, and Helene E. Bargmann. A Synopsis of the Siphonophora. British Museum (Natural History), 1965.