Hexelasma americanum Pilsbry, 1916

Young, Paulo S., 2001, Deep-sea Cirripedia Thoracica (Crustacea) from the northeastern Atlantic collected by French expeditions, Zoosystema 23 (4), pp. 705-756 : 747-748

Hexelasma americanum Pilsbry, 1916 ( Fig. 30 )

Hexelasma americanum Pilsbry, 1916: 330 , fig. 98, pl. 69, figs 1-3. — Young 1998c: 117 (with synonymy). MATERIALEXAMINED. — SEAMOUNT 2, stn DW 198, 31°18.60’N, 28°35.05’W, 1240 m to 31°18.79’N, 28°34.88’W, 1250 m, 2 specimens and disarticulated plates, rc 12.6 to 14.9 mm (MNHN Ci 2918). — Stn DW 200, 31°19.07’N, 28°36.01’W, 1060 m to 31°19.27’N, 28°35.92’W, 1100 m, 64 specimens and 6 empty shells, rc 3.6 to 19.4 mm (MNHN Ci 2919, MNRJ 13938). — Stn DW 203, 31°09.52’N, 28°43.52’W, 845 m to 31°09.67’N, 28°43.38’W, 990 m, 11 specimens and disarticulated plates, rc 13.1 to 28.9 mm (MNHN Ci 2920, MNRJ 13939). — Stn DW 221, 32°17.84’N, 28°15.32’W, 1180 m to 32°18.03’N, 28°15.47’W, 1160 m, 11 specimens and disarticulated plates, rc 10.0 to 16.4 mm (MNHN Ci 2921, MNRJ 13940). — Stn DW 222, 32°20.81’N, 28°15.66’W, 1150 m to 32°21.02’N, 28°15.72’W, 1150 m, 29 specimens and disarticulated plates, rc 12.3 to 19.7 mm (MNHN Ci 2922, MNRJ 13941). — Stn DW 243, 33°13.18’N, 29°08.24’W, 1420 m to 33°13.47’N, 29°07.85’W, 1360 m, 1 specimen and disarticulated plates, rc 22.4 mm (MNHN Ci 2923). — Stn DW 262, 34°23.36’N, 30°29.06’W, 1160 m to 34°23.58’N, 30°29.35’W, 1000 m, 4 specimens and disarticulated plates, rc 11.7 mm (MNHN Ci 2924). — Stn DW 264, 34°24.74’N, 30°30.77’W, 830 m to 34°24.85’N, 30°31.08’W, 795 m, 2 specimens and disarticulated plates, rc 14.2 to 20.3 mm (MNHN Ci 2925). — Stn DW 271, 33°54.08’N, 30°09.33’W, 1220 m to 33°54.14’N, 30°09.34’W, 1220 m, 27 disarticulated plates (MNHN Ci 2926). — Stn DW 277, 33°59.92’N, 28°20.56’W, 1000 m to 33°59.64’N, 28°20.81’W, 945 m, 12 specimens and disarticulated plates, rc 9.5 to 25.0 mm (MNHN Ci 2927, MNRJ 13942).

REMARKS

Most of the specimens have the carinal plate significantly higher than the other plates ( Fig. 30A, B ). The outline of the terga varied with the spur varying from distally rounded to a more square termination ( Fig. 30 C-E).

Hexelasma americanum was described from the western Atlantic by Pilsbry (1916: 330) based on specimens taken on the Blake Plateau, Florida. It was also recorded from the Mid-Atlantic Ridge and Azores region ( Young 1998b: 66, c: 117). The new samples, consisting a large number of specimens, suggest that H. americanum is a common species on the eastern Atlantic seamounts, between 715 and 1420 m.

Figures

FIG. 30. — Hexelasma americanum Pilsbry, 1916, SEAMOUNT 2, stn DW 222; A, top view; B, lateral view; C-E, terga outlines. Note the variation on the shape of the spur. Scale bar: 10 mm.