Benson 1966 - Eucyrtidium aquilonaris

Smooth test spindle-shaped, with 3-6 unequal to subequal abdominal joints separated by indistinct strictures coincident with narrow hyaline rings which in a few specimens are raised internally. Distal joint constricted, in many specimens with a hyaline cylindrical peristome which is latticed distally in a few tests suggesting an additional distal joint; middle abdominal joints the broadest. Shell wall of variable thickness (2-8 µm).Pores relatively large, subequal, generally subrectangular but circular to elliptical in some specimens, double-contoured in tests with thick walls, arranged in 1-5 transverse rows per joint, of equal size in each row, generally separated by wide intervening bars. Thorax campanulate, generally separated from abdominal region by a distinct stricture; pores similar to those of the abdominal joints. Structure of the cephalis the same as in Siphocampium cf. cornutella. Apical spine lacking or generally short, indistinct. Dorsal and primary lateral thoracic ribs indistinct. Hyaline, ventral cephalic tube more prominent than in S. cf.cornutella, not horizontal, and attached to the proximal portion of the thorax but ascends ventrally.

Measurements: based on 25 specimens from stations 27, 34, and 95: maximum length of test 111-162 µm, maximum breadth 60-80 µm; length of cephalis 14-20 µm, of thorax 18-25 µm; breadth of cephalis 15-31 µm, of thorax 38-52 µm; length of apical spine 0-12 mm, of ventral tube 6-15 mm; breadth of hyaline peristome 39-49 µm.

Remarks: Haeckel's illustration of Siphocampe erucosa Haeckel agrees in all details with the Gulf species. It has double-contoured pores, which is characteristic of tests with thick walls, and a constricted hyaline peristome. In general shape of the test, the nature of its pores and abdominal joints the following species are similar to the Gulf species except that they lack the ventral tube, a feature which in some specimens is absent or easily overlooked: Eucyrtidium tumidulum Bailey (1856, p. 5, Pl. 1, fig. 11) from the Sea of Kamchatka; E. tumidulum (Bailey) Ehrenberg (1862, p. 299; 1873b, Pl. 2, fig. 12) from the Davis Straits in the North Atlantic; E.hispidum Ehrenberg (1862, p. 298; 1873b, Pl. 2, fig. 13) from the same region; and E. euporum Ehrenberg (1873a, p. 309; 1873b, Pl. 4, fig. 20) from the North Atlantic.

Distribution: This species is nearly cosmopolitan in the Gulf. It is absent at stations 64, 99, 130, 133, 151, 194, and all those to the north. It is very rare at all stations where it is present except at stations 90 where it is nearly common (1.6%) and 95 where it is common (5.6%) and is the fourth most abundant species. Its increased frequency at the former reflects its response to upwelling along the Baja California coast, but its high frequency at the latter may be the result of lateral transport from the western Gulf margin. It responds to upwelling at no other locality in the Gulf. Its sparse distribution in the northern Gulf and its slightly greater frequency and more general distribution in the southern Gulf indicate that it is primarily an oceanic species. Siphocampe erucosa Haeckel was reported from the central tropical Pacific at Challenger station 270.This species, therefore, may be confined to tropical regions unless the species mentioned in the remarks are identical with it; then it would have a cosmopolitan distribution. \ From: Benson, 1966, p. 527-530; pl. 35, figs. 18-20:Siphocampium erucosum (Haeckel)Siphocampe erucosa Haeckel, 1887, Challenger Rept., Zool., vol. 18, pp. 1500-l501, Pl. 79, fig. 11.

Nigrini 1977 - Eucyrtidium aquilonaris

Description: Shell typically heavy, thick-walled, but early forms are not so robust. Constrictions (other than collar and lumbar strictures) unevenly spaced and all strictures usually obscure externally. Shell spindle- shaped wi th four or five post-cephalic segments, the fourth being widest. Cephalis hemispherical wi th small irregular pores; vertical tube robust, cylindrical, directed obliquely upwards at approximately 45°. Apical horn very small, needle-like. Thorax inflated with two or three transverse rows of large subcircular pores. Subsequent segments wi th three to six (usually four) transverse rows of very closely spaced circular pores. Thickness of shell makes each pore appear to have a ring around it. Shell narrows distally, terminating in smooth peristome of variable width; peristome may have single row of pores. Termination smooth or with an undulating margin.

Dimensions: Total length 110-155µ; maxi mum breadth 60-90µ.

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