# Cirroteuthis

Cirroteuthis muelleri, also known as the big-finned jellyhead, was the first cirrate octopus species (and genus) to be scientifically described (in 1836). It is closely related to the genus Cirrothauma within the family Cirroteuthidae. The species is restricted to the Arctic Ocean and far North Atlantic (specimens from the southern hemisphere and Pacific have been attributed to a new species Cirroteuthis kirrilyae Verhoeff & O'Shea, 2025).

## Description

Cirroteuthis muelleri can reach a maximum length of 400 mm (mantle length 170 mm). Statements that C. muelleri reaches up to 1.5 m total length are erroneous (and involve unidentified Cirrothauma, then regarded as Cirroteuthis sp., being mistakenly assumed to be C. muelleri). It is off white or pale purple, with the inner side of the arms and the webs being brownish-purple.
The head has well developed eyes with lenses. The upper and lower beaks are thin and relatively weak. The body is gelatinous and fragile. The arms are nearly equal in length. A pair of translucent webs joins the dorsal and ventral sides of the arms together and the webs terminate at a nodule. The first 7 or 8 suckers are cup-shaped and raised on thick stalks, numbers 2 and 3 being the largest. There are a further 30 or so smaller suckers with delicate stalks. Between the suckers are conspicuous cirri up to 19 mm (0.75 in) long. These are elongate, fleshy tendrils set along the sides of the oral surface of the arms, the longest being in the mid-arm region. Both the suckers and the cirri do not extend as far as the tip of the arm.
The fins are elliptical when viewed from the side. They are wide, and longer than the width of the head. The aperture of the mantle is narrow and the funnel is long.

## Distribution

Cirroteuthis muelleri is a deep sea species. It is found in cold seas in the boreal Arctic and the far north Atlantic Ocean. Specimens of Cirroteuthis from around Australia, New Zealand, and possibly the central and northeastern Pacific have been allocated to a new species, Cirroteuthis kirrilyae Verhoeff & O'Shea, 2025 (previously referred to Cirroteuthis cf. muelleri).

## Habitat

Cirroteuthis muelleri is benthopelagic, meaning it is found swimming or drifting in the 10 m (33 ft) or so immediately above the sea bed. It is usually found at depths of over 2,000 m (6,600 ft). At these depths, practically no light penetrates, the temperature is about 4 °C, and observation is only possible by submersible, which makes these octopuses difficult to collect. Their ecology and biology are little known, but they seem to be fairly common in the seas around Greenland.

## Biology

In a study of Arctic cephalopods, three specimens of Cirroteuthis muelleri, all female, were caught near the ocean floor at 3,000–3,300 m (9,800–10,800 ft). The eggs were found to be large and were laid on the bottom, singly. The diet of C. muelleri (from stomach contents of 18 specimens) was found to comprise small crustaceans (Calanoida, Mysidacea, Isopoda) and polychaetes (Polynoidae), all small benthic or epibenthic prey items. The largest mysids consumed were estimated at 14.6 mm long, and the largest polychaete was estimated at 24.3 mm.