(Fig. 4)
Nausithoe atlantica Broch, 1913: 9–10, pl. I figs 1–4.
Holotype not known, possibly not extant.
Material examined: NHM 1982.11.30.125, NHM 1982.11.30.128 (two specimens from Portugal 1982, no information on depth) and MBARI database (identity-reference 35 from Gulf of California 2015, USA 25°45’N 109°85’, depth: 2,590m; identity-reference 24 from coast of Oregon 2006, USA 45°40’N 126°72’W, depth: 2,334m).
Diagnosis: medusa—isodome bell with dark colored umbrella.
Description: Based on Broch (1913), Russell (1956), and Kramp (1961), due to poor condition of specimens. Adult medusa up to 35 mm in diameter, 19 mm of this the central disc; umbrella smooth, dark yellowish-brown (almost black); somewhat arched central disc; slightly elongate marginal lappets with rounded margins; rhopalia with statocyst and deeply colored ventral sensory bulb; circular to slightly oblong gonads; more than 160 gastric filaments in total. No information about polyp stage.
Type locality: North Atlantic (36°53’N 29°47’W, 500 m depth).
Distribution: North Atlantic and Pacific coasts of North America.
Remarks: The only two specimens examined (NHM 1982.11.30.125, NHM 1982.11.30.128) were damaged, precluding the observation of important characters. Both animals had a smooth umbrella with remnants of redbrownish pigmentation (almost vanishing).Tentacles with a very thick base. Gonads disc-shaped (early development), elongated distally and near to the margin of coronal muscle. It was not possible to see the gastrovascular cavity and lappets, and the rhopalia were too damaged to be observed and described. Tentacles were as long as the estimated total diameter of specimens, around 20 mm. Based on MBARI images, gonads apparently form two aboral extensions in later development.