S91

Hymeniastrum euclidis (Haeckel)

Hymeniastrum euclidis Haeckel, 1887, p. 531, pl. 43, fig. 13; Benson, 1966, p. 222, pl. 12, figs. 1-3

?Cyclastrum? sp., Ling and Anikouchine, 1967, p. 1487, pls. 191, 192, figs. 1, 2

DESCRIPTION "Discoidal test with three arms of nearly equal size and similar shape, elliptical in section, separated by nearly equal angles; a layered spongy patagium generally present but rudimentary or absent in several specimens, thicker distally along its margin than proximally where it is thin and delicate, when fully developed subtriangular in shape. Central region of test circular to subtriangular in outline, consisting of 4-5 concentric discoidal latticed shells, therefore, biconvex in side view. Arms very narrow proximally, increasing only gradually in breadth for most of their length, terminating in broad bulbous tips, a few of which were observed with 3-4 internal concentric shells or rings. Internal structure of arms consisting of numerous (13-25) concentric, irregular, partial rings, subequally spaced, more or less perpendicular to the outer latticed cover of the arm. In most specimens the internal structure of the test is not distinct and the center as well as the arms appear spongy. The arms and center covered with a generally distinguishable, small-pored latticed sheath. Several specimens were observed with 1-3 terminal spines on one or more of the arms, 4-31 microns in length." (from Benson, 1966).

DIMENSIONS "based on 30 specimens from stations 27, 34, 46, 56, 60, 64, 71, and 81: angle A 111 degrees - 142 degrees, mean 126 degrees; angle B 95 degrees - 126 degrees, mean 111 degrees; angle C 111 degrees - 133 degrees, mean 123 degrees; ratio of angle A to angle B 0.98-1.49, mean 1.13; ratio of angle C to angle B 0.88-1.29, mean 1.11; diameter of outer concentric shell of central region 55-84 microns; length of odd arm (if not distinguishable an arm was chosen at random) 96-209 microns, of each of the two similar arms 96-205 microns, and 101-197 microns, minimum breadth of odd arm 27-48 microns, of each of the two similar arms 27-47 microns and 26-48 microns; maximum breadth of bulbous tip of odd arm 50-112 microns, of each of the two similar arms 48-123 microns and 49-114 microns; length of base of triangular test 218-411 microns, of altitude 203-396 microns." (from Benson, 1966).

REMARKS

1. For a more complete synonymy see Nigrini, 1970.

2. The specimens figured by Benson (1966) are larger than that shown by Nigrini (1970). For additional illustrations see Benson (1966).

Plate 12, figure 3

S92

RECENT DISTRIBUTION

1. Benson, 1966; "This species is cosmopolitan but rare in the Gulf [of California]... It has a higher than average frequency in the southern Gulf with highest frequency (1.4%) at station 64 located in a region of upwelling. It does not increase, however, at other stations located within areas of upwelling. Its general decrease northward in the Gulf suggests its greater affinity for oceanic water masses."

2. Nigrini, 1970, fig. 16; belongs to a tropical assemblage derived by recurrent group analysis of North Pacific samples, but the species ranges too far north to be useful in down-core analysis. 3. Molina-Cruz, 1975, Code S18; not used in factor analysis of southeast Pacific assemblages; cf. Appendix 10 for percent S18 at each station.