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Druppatractus variabilis Dumitrica, 1973

Description - Add description

Benson, 1966, p. 177-180; pl. 7, figs. 2-6:

Druppatractus cf. pyrifomis (Bailey)

?Haliomma? pyriformis Bailey, 1856, Amer. Jour. Sci , vol 22, ser. 2, p. 2, Pl. 1, fig. 29.

Test consisting of an inner pear-shaped shell joined to an outer, generally ellipsoidal, but in several specimens spherical, latticed shell by 20-40 or more thin, three-bladed, radial beams in addition to two heavier three-bladed beams generally coaxial with the major axis of both shells. Latter beams continue outward as three-bladed polar spines of unequal length (in a few tests polar spines absent), the spine continuous with the beam that arises from the small lobe of the pear-shaped inner shell being the longer; in several specimens the lesser spine and its beam dislocated as much as 30° from the major shell axis. Additional radial spines continuous inward as beams are present in several specimens, generally one to two in number, in one specimen as many as 10, generally located near the pole with the shorter polar spine but near the larger spine in a few specimens, of variable length, in many specimens as long as or longer than the polar spines. Outer shell with wall of variable thickness, with relatively large, subequal, subcircular to subpolygonal pores, hexagonally arranged, 6-9 (generally 7-8) on half the minor circumference, with hexagonal frames, in a few specimens as high as l5-20 µm (particularly in diatomite regions of the Gulf), in a few specimens frames absent; surface ranges from smooth to thorny, in a few specimens with thin conical spines arising from the nodes of the intervening bars. Inner shell constantly pear-shaped but appears spherical in end view, aligned with the major shell axis, with generally smooth surface, with subequal, subcircular to subpolygonal pores, about one-third the size of the pores of the outer shell, subregularly arranged, 5-8 (generally 7-8) on half the minor circumference, generally without polygonal frames.

Measurements; based on 30 specimens from station 27: major diameter of outer shell 69-105 µm, of inner shell 37-58 µm; minor diameter of outer shell 58-101, µm, of inner shell 27-44 µm; length of greater polar spine (when present) 6-77 µm, of lesser polar spine (when present) 6-33 µm; of accessory radial spines 2-4l µm.

Remarks. No reference to this species could be found in the literature. Bailey's illustration of what the writer interprets as the pear-shaped medullary shell of either this species or D. irregularis Popofsky shows a slightly longer spine (rudimentary beam?) arising from the small lobe of the shell and a smaller one from the opposite pole, a feature which is characteristic of this species from the Gulf. Because end views of specimens belonging to this species show a spherical instead of pear-shaped inner shell, it is possible that such forms were described previously under a different genus.

Distribution. This species is one of the predominant members of the Gulf assemblage. It is common or abundant in the southern half of the Gulf and is common to rare in the northern half. It is absent at stations 203, 208, and 214; rare at stations 91, 133, 151, 191, 192, 194, and 206; abundant at stations 71 (13.0%) and 90 (22.2%); and common at all others. It is the predominant species at stations 64, 71, and 90. Its frequency at station 90 is the greatest for any species at any of the Gulf stations studied, but at the next station to the east, 91, it is rare, having nearly its lowest observed frequency in the Gulf. At stations 92, 93, 95, and 99 it is common and undergoes no abrupt changes in its frequency. Its high frequency at station 90 is probably related to upwelling in this region, but its very rare occurrence at station 91 is difficult to explain. This station is located near Isla Santa Catalina, and perhaps local conditions of the water masses near this island are unfavorable for this species. In the southern half of the Gulf it is as common at the marginal stations 64 and 56 as it is at the farther offshore stations 27 and 60, a fact which may be explained by upwelling. North of stations 90-99, its frequency is sharply reduced, never reaching greater than 3.8%, and it has, in general, greater frequencies in the axial portion of the Gulf rather than in near shore areas. The fact that this species occurs commonly as far north as station 184 indicates that it is tolerant of the slightly higher salinity and temperature here, but its greater frequency in the southern part of the Gulf indicates its greater affinity for oceanic water masses.
If this species is the same as the pear-shaped shell reported by Bailey (1856, P1. 1, fig. 29) from the Sea of Kamchatka, it occurs at high as well as low latitudes. Without positive identification, however, no information on its oceanic distribution is available.

Benson 1966











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