Hemithyris psittacea (Gmelin, 1790)
Anomia psittacea Gmelin, 1790: 3348.
Rhynchonella psittacea Davidson, 1887: 163–168, pl. 24, figs. 1–8.
Hemithyris psittacea Dall, 1920: 284–286; Hatai, 1940: 197–203, pl. 6, figs. 64–67, 72–73, 77–78; Konzhukova, 1957: 71–73, pl. 9, figs. 13–16; Zezina, 1997: 44–45, fig. 27.
Description. Shells are up to 30 mm in length, from grayish-brown to black, they are triangular in plan with rounded anterior margin, the outer surface has thin radial stripes, pores are absent, shells of young specimens are hemitranslucent. Anterior commissure is uniplicate (convex to brachial valve). Crura reach ¼ length of brachial valve, they are flat and each of them is reinforced with oblique rib from sides to the centre of the shell. Two spirals of lophophore (up to 5 turns in each) are forming cones with tops directed to brachial valve and slightly inclined to the middle line of shell. There are no spicules in soft tissues.
Distribution. The species has circumpolar range from the Arctic Ocean up to the Bay of Maine and north-eastern coast of Great Britain in the Atlantic, and to Kyushu (Japan) and Oregon (USA) in the Pacific. In the northern part of the Sea of Japan H. psittacea is found in isolated instances near western coast of Hokkaido and off Tsugaru Strait without data on the depth of collecting (Konzhukova, 1957).
Ecological data. Vertical distribution: from low water line down to 2078 m (5–916 m in Arctic and Far-East Russian seas). Near Iturup Island from the side of the Sea of Okhotsk the species forms population with density up to 50 sp./m2 at the depth of 10 m (Zezina, 1997).
Remarks. Black and almost smooth specimens collected off the eastern coasts of Japan are considered sometimes as separate species Hemithyris woodwardi (=Rhynchonella woodwardiAdams, 1863), which Hatai (1940) offered to consider as subspecies Rhynchonella psittacea woodwardi.
References:
The World Register of Marine Species