(Figs 3, 4)
Metacyphocaris Helgae Tattersall, 1906: 29, pl. 3 fig. 1, pl. 4. — Stephensen, 1912a: 88. — Stephensen, 1912b: 613. — Stephensen, 1913: 113. — Stephensen, 1915: 38. — Stephensen, 1923: 54. — Schellenberg, 1926b: 216, figs 26c, 27. — Schellenberg, 1927: 666, fig. 60. — Pirlot, 1929: 8. — Schellenberg, 1929: 196. — K.H. Barnard, 1932: 37, fig. 5. — Stephensen, 1932: 354. — Stephensen, 1933: 9. — Chevreux, 1935: 28. — Thorsteinson, 1941: 60, pl. 3 figs 31-38. — Shoemaker, 1945: 189. — J.L. Barnard, 1958: 95. — Birstein & Vinogradov, 1958: 222. — Birstein & Vinogradov, 1960: 171. — Gurjanova, 1962: 79, fig. 14. — Hurley, 1963: 22, fig. 3. — Birstein & Vinogradov, 1964: 156. — O'Riordan, 1969: 32. — Thurston & Allen, 1969: 361. — Vader, 1983: 140 (table 1). — Umezu, 1984: 128. — Austin, 1985: 601. — Costello et al., 1989: 32. — Barnard & Karaman, 1991: 502. — Palerud & Vader, 1991: 38. — Lopes et al., 1993: 209. — Thurston, 2001: 684 (table 2).
Type localities (for syntypes). 40 miles north by west of Eagle Island, County Mayo, Ireland, eastern North Atlantic Ocean, [approx. 54°30'N 11°30'W], 1152 m over 1189+ m; same locality, 1371 m over 1829+ m; west of Porcupine Bank, eastern North Atlantic Ocean, 53°07'N 15°06'W, 1371 m over 1573 m; 50 miles north by west of Eagle Island, County Mayo, Ireland, eastern North Atlantic Ocean, [approx. 54°30'N 11°30'W], 1097 m over 2195 m; same locality, 2113 m over 2195 m.
Material examined. 1 specimen, immature, 11.5 mm, MV J15797, south of Point Hicks, Victoria, Australia, 38°27.20'S 149°09.70'E, 8 m rectangular midwater trawl, 22 July 1986, M.F. Gomon et al., RV Franklin, stn SLOPE 24.
Distribution. Atlantic, Indian and Pacific Oceans, between 65°N and 40°S; to 4740 m depth (see remarks).
Remarks. Tattersall (1906: 30), in his original description of Metacyphocaris helgae, said it had no mandibular palp, only a "very small rounded tubercular appendage". We have examined a specimen from the syntype series and confirm this description. Tattersall used this character to separate Metacyphocaris from Paracyphocaris. K.H. Barnard (1932) reported material of M. helgae from the South Atlantic Ocean with a rudimentary 2-articulate mandibular palp. Shoemaker (1945) also reported material with a rudimentary 2-articulate mandibular palp from Bermuda in the western North Atlantic Ocean and Hurley (1963) reported material with a 1- articulate palp from the San Nicholas Basin, eastern Pacific Ocean. There are now 18 literature reports of M. helgae material, recording more than 100 specimens. Most are not illustrated or described so it is not possible to assess the variation in the mandibular palp or any other characters which might indicate separate species. The single specimen we record here has no mandibular palp and matches very well with Tattersall's type material.
The depth range cited above is very unlikely. According to Thurston (2010 in litt.) this is ‘the bottom depth under the 0–4990 m haul listed in Birstein & Vinogradov (1960). Virtually all Birstein & Vinogradov hauls were made with open nets and the depths quoted are metres of wire out. The same is true for most mid-water hauls, even those made in horizontal mode. I have unpublished data for M. helgae collected in the North Atlantic at 60N20W, 53N20W, 40N20W and 30N23W to depths of 2000 m or more. Based on an analysis of more than 200 specimens obtained using the opening/closing IOS RMT1+8 nets, the species occurs in all layers from 600–700 m down to 1250–1500 m. Single specimens were caught at 500–600 m and 1500–2000 m.’