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.