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Hymeniastrum euclidis Haeckel, 1887

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Benson, 1966, p. 222-225; pl. 12, figs. 1-3:

Hymeniastrum euclidis Haeckel, Popofsky

Hymeniastrum euclidis Haeckel, Popofsky, 1912, Deutsche Südpolar Exped., vol. 13, pp. 136-137, text fig. 51.

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 µm in length.

Measurements; based on 30 specimens from stations 27, 34, 46, 56, 60, 64, 71, and 81: angle A 111°-142°, mean 126°; angle B 95°-l26°, mean 111°; angle C 111°-l33°, mean 123°; 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 µm; length of odd arm (if not distinguishable an arm was chosen at random) 96-209 µm, of each of the two similar arms 96-205 µm, and 101-197 µm, minimum breadth of odd arm 27-48 µm, of each of the two similar arms 27-47 µm and 26-48 µm; maximum breadth of bulbous tip of odd arm 50-112 µm of each of the two similar arms 48-123 µm and 49-114 µm; length of base of triangular test 218-411 µm, of altitude 203-369 µm.

Remarks. This species is similar to Hymeniastrum koellikeri [=Dictyocoryne profunda] but differs from it in the presence of narrower arms with bulbous tips, a smaller central region with fewer concentric shells, the lack of a clearly distinguishable odd arm in most specimens, the presence of arms nearly equally disposed in most specimens, and in the presence of a patagium that is thicker distally than proximally.
Although the shape of the arms of this species is similar to Haeckel's illustration (1887, P1. 143, fig. 13) of Hymeniastrum euclidis, the patagium is not; however, specimens from the Gulf may be incomplete. Examination of Haeckel's type material of this species may establish its identity with the Gulf species. Popofsky's illustration (1912, text fig. 51) of H. euclidis is of a form with an incomplete patagium. His interpretation of the internal structure agrees with the writer's, and the shape of the arms is identical with that of the Gulf species; therefore, the Gulf species is identified as H. euclidis on the basis of comparison with Popofsky's, not Haeckel's, figure.

Distribution. This species is cosmopolitan but rare in the Gulf. It is absent at stations 136, 191, 194, 203, and 214. 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.
Popofsky (1912, p. 137) reported .this species from approximately 20° N. latitude in the central Atlantic. Haeckel (1887, p. 531) reported H. euclidis from the surface of the equatorial Pacific at "Challenger" stations 270-274. This species, therefore, appears to be a tropical species. It has not been reported from high latitudes.
Benson 1966











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