Monobrachium parasitum Mereschkowsky, 1877:220–229, pl. 5 figs 1–6, pl. 6 figs 7–14. Broch 1916:42–43, text-fig. L. Fraser 1918:131–133, pl I figs 1A,B,C; 1921:7, text-fig. 3; 1944:44–45, pl. 2 figs 7a,b,c,d. Hand 1957:84–88, figs 1–2. Marche- Marchad 1963:1347, 1349; 1975:569–583. Campbell 1967:431. Rees 1967:218–219. Robins 1972:76, 79, 80. Ramil 1988:478–483, pl. XXIII A,B,C,D. Besteiro et al. 1990:91–796, fig. 2. Kubota 1991:1–6, figs 1,2. Stepanjants et al. 1997:458; 2006:217. Jarms and Mühlenhardt-Siegel 1998:125–139 fig 3. Schuchert 2001:157–158, textfig. 138 A,B,C. Passos 2003:53. Passos et al. 2005:372–374, fig 1. Altuna 2007:690.
Monobrachium parasiticum (sic.) Mereschkowsky, 1877. Wagner 1890:273–309, pls VIII IX, figs 1–21. Medel and López-Gonzáles 1996:207. Bouillon et al. 2004:206, fig. 120A.
Bay of Onega, White Sea, 9 m depth, on the pelecypod Macoma calcarea (= Tellina calcarea).
Colonies reptant, consisting of many zooids arising from a network of stolons adhering to valves of host bivalve shell (Figures 2A, 3A) and extending from surface to margin, with a number of free ends projecting beyond it by means of typical dactylozooids (see Figures 2A, 3A); polyps cylindrical, rising directly from stolons, terminating in a large mouth, bearing nematocysts over entire length (Figure 2C), each polyp provided with a long and vigorous tentacle having large nematocysts (microbasic euryteles) scattered over its full length (Figure 2D). One colony fertile, with a single globular gonophore rising from the stolon by means of a small peduncle, resembling a reduced medusoid, gonophore with a thick periderm capsule filled with masses of (probable) female generative cells placed along the radial canals (Figure 2A).
Most previous records of M. parasitum are from the northern hemisphere. Its original description is from the White Sea by Mereschkowsky (1877). Other records include those of Stafford (1912 apud Fraser 1944), in the Gaspé region (Atlantic coast of Canada); Fraser (1918), from Vancouver Island, British Columbia (Pacific coast of Canada); Hand (1957), in shallow waters of California and Baja California; Naumov (1969), in the southernmost part of the Sea of Okhotsk, Russia; Ramil (1988), Besteiro et al. (1990), and Altuna (2007), in Galicia, Iberian Peninsula; Medel and Lòpez-González (1996), in the Mediterranean; and a doubtful record from the Sea of Yûbetsu, Hokkaido, Japan, by Kubota (1991). Its distribution, as given by Naumov (1969), extends from the “White, Barents, Kara, and Chukchi seas, seas of Okhotsk and Japan; coasts of Spitsbergen and western Greenland; Atlantic and Pacific coasts of Canada; coast of California.” In the southern hemisphere, records of M. parasitum are from the South Orkney Islands, Elephant Island, and the region on the west side of the Antarctic Peninsula (Stepanjants et al. 1997; Jarms and Mühlenhardt-Siegel 1998).