N61

Eucyrtidium acuminatum (Ehrenberg)

Lithocampe acuminatum Ehrenberg, 1844a, p. 84

Eucyrtidium acuminatum (Ehrenberg), Nigrini, 1967, p. 81, pl. 8, figs. 3a b

DESCRIPTION

"Cephalis simple, spherical, with numerous small subcircular pores. Short conical apical horn usually present. Primary lateral and dorsal spines continue as ribs in the thoracic wall for its entire length; rarely, these become external, forming wings. Collar stricture indistinct.

"Thorax small, conical, sometimes slightly inflated; thick-walled, with subcircular pores aligned approximately longitudinally. Lumbar stricture not indented externally.

"Abdomen and 4-5 post-abdominal segments, thick-walled, of approximately equal length, expanding distally to a maximum breadth at about the third post-abdominal segment; then, in complete specimens, narrowing to a quite constricted mouth. No peristome or terminal teeth but, rarely, with a short cylindrical terminal tube. Pores small, subcircular, aligned longitudinally, 4-6 per segment in a vertical series. Final segments may become irregular." (from Nigrini, 1967).

"Complete specimens were rarely observed. Most forms seen were sub cylindrical, tapering to cephalis." (from Sachs, 1973).

DIMENSIONS

"Total length 119-182 microns. Diameter of cephalic 9-13 microns. Length of thorax 9-18 microns. Maximum breadth 63-81 microns." (from Nigrini, 1967).

"width of cephalis, 21 +/- 2 microns; maximum width of specimen, 71 +/- 13 microns; overall length, 110 +/- 8 microns; based on measurements of 17 specimens" (from Sachs, 1973).

REMARKS

1. For a more complete synonymy see Nigrini, 1967 and Petrushevskaya, 1971.

Plate 24, figures 3a,b

N62

RECENT DISTRIBUTION

1. Nigrini, 1967, fig. 43; "Indian Ocean occurrences - E. acuminatum is very sparsely distributed in low latitudes, but is abundant (up to 13% of the described population) in middle latitudes. It appears to be a reliable and potentially useful member of the middle latitude assemblage."

2. Nigrini, 1970, fig. 28; belongs to a transitional assemblage derived by recurrent group analysis of North Pacific samples.

3. Sachs, 1973, Code 20N, "Patchy distribution, dominantly in Transitional waters. Maximum abundance about 4% in the surface study.

4. Lozano, 1974, Fig. IV-8; "It is always present in sediments under subtropical waters except for the westernmost Atlantic and in core V29-81 in the Indian Ocean. It reaches a maximum abundance of 1.5 percent in core V27-193 which is located at the subtropical convergence in the Atlantic Ocean. Minimum February sea surface temperature under which it is present is 8 degrees C in the Atlantic (RC11-67) and 6 degrees C in the Indian Ocean (V29-88)."

5. Molina-Cruz, 1975, Code N10; not used in factor analysis of south-east Pacific assemblages; cf. Appendix 10 for percent N10 at each station.

6. Robertson, 1975, "This species loads most heavily in factor 2 (subtropical). At present this species is largely absent north of 45 degrees N. At 18,000 YBP it has a similar distribution but with slightly lower abundances."