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Pterocanium praetextum eucolpum Haeckel, 1887

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Benson, 1966, p. 405-408; pl. 27, figs. 3, 5 (not 4):

Pterocanium prosperinae Ehrenberg

Pterocanium prosperinae Ehrenberg, 1859, Akad. Berlin, Monatsb. (1858), p. 34; l873b, Acad. Berlin, Abhandl. (1872), Pl. 11, fig. 22.
?Pterocanium charybdeum Müller, 1859, Akad. Berlin, Abhandl. (1858), pp. 43-45, Pl. 6, figs. 7-10. [= Podocyrtis charybdea Müller, 1857, Akad. Berlin, Monatsb. (1856), pp. 492-493].

Cephalis subspherical, smooth to rough, with small, subequal, circular pores; separated from the thorax by a distinct change in contour and in a few tests by an indistinct collar stricture. Apical horn heavy, conical to three-bladed, straight to slightly curved, nearly vertical to slightly dorsally ascending, extends from the apical bar which is a dorsal rib in the wall of the cephalis. A short, thin, conical vertical spine extends from the vertical bar. Four collar pores present at the base of the cephalis, in a few tests, six. Thorax campanulate, without prominent shoulders or swellings, with its basal portion turned inward and terminating in a continuous internal septal ring. Pores of the thorax small, of nearly equal size, regularly arranged in longitudinal rows, subcircular to hexagonal, generally with polygonal frames. Surface of thorax generally rough, in several specimens with scattered thin, conical spines. Thoracic ribs extending from the dorsal and primary lateral bars of the collar region are present but indistinct; each rib extends as the outward projecting blade of the three-bladed feet; this blade originates from just below the level of maximum thoracic breadth, and in lateral outline it is generally separated from the thorax by a slight constriction. The other two blades of the feet lie in the plane of the abdominal lattice, and the proximally latticed portion of each is joined by a short bar to the internal septal ring. The abdomen is of variable stage of development; in fully developed forms it consists of three convex outward lattices, each located between two of the feet. The pores of the abdomen are large and subcircular to elliptical on either side of each foot and along the inner septal ring, the remainder of the lattice consisting of small, subequal, subcircular to irregular pores. Surface of the abdomen generally smooth. Basal margin of each of the three lattices between feet generally incomplete but with convex downward outline when complete. Feet either straight, with convex outward curvature, or, in a few tests, with slight concave outward curvature.

Measurements; based on 30 specimens from stations 27, 34, 46, 56, 60, and 81: length of cephalis 20-27 µm, of thorax 55-98 µm, of abdominal lattice 37-71 µm; breadth of cephalis 25-31 µm, of thorax 90-157 µm, of completely developed abdomen (3 specimens) 107-127 µm; length of apical horn 25-65 µm, of vertical spine 6-15 µm, of feet 90-228 µm; maximum distance between tips of feet 137-271 µm.

Remarks. This species is similar to Pterocanium praetextum Ehrenberg from the Gulf but differs from it in the presence of a campanulate thorax without prominent swellings or shoulders between the thoracic ribs and by the larger size of the thorax. Ehrenberg’s illustration of P. prosperinae Ehrenberg (1872, Pl. 11, fig. 22) is similar to the Gulf species in having a campanulate thorax, equal, subregularly to regularly arranged thoracic pores, indistinct thoracic ribs, feet that are latticed proximally, and a rudimentary abdominal lattice present between the feet. Müller’s illustrations of P. charybdeum Müller (1859, Pl. 6, figs. 7-10) are similar to the Gulf species, but his drawings lack details; therefore, identification of the Gulf species with his species is only tentative.

Distribution. This species is rare but cosmopolitan in the Gulf, being absent only at stations 184, 192, 203, 206, 208, and 214. Its average frequency in the southern half of the Gulf is greater than that in the northern half; therefore, it is a predominantly oceanic species. Its maximum frequency is at station 46 in the southern axial portion of the Gulf. It does not undergo any increase at stations located within areas of upwelling.
Both Pterocanium prosperinae Ehrenberg and P. charybdeum Müller are present in the Mediterranean Sea. This species, therefore, is widespread in Recent tropical seas.
Benson 1966


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