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Pseudodictyophimus platycephalus (Haeckel, 1887)

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Benson, 1966, p. 385-386; pl. 25, figs. 7-9:

Dictyophimus platycephalus Haeckel

Dictyophimus platycephalus Haeckel, 1887, Challenger Rept., Zool., vol. 18, p. 1198, Pl. 60, figs. 4,5.
?Dictyophimus brandtii Haeckel, 1887, op. cit., p. 1198, Pl. 60, fig. 6.

Cephalis subhemispherical or cap-like, small, barely distinguishable except for a ventral stricture separating it from a very broadly conical but short thorax developed between three widely splayed feet. Cephalis smooth with small, unequal, subcircular pores; with a nearly vertical apical spine or horn extending from the straight apical bar of the short dorsal cephalic face which is almost completely covered by the two dorso-lateral lobes of the upper part of the thorax; a thin, conical, generally short vertical spine arises from the ventral stricture between cephalis and thorax and ascends ventrally. Thorax developed between the three feet, with three lobes proximally, each lobe present between the dorsal and primary lateral thoracic ribs; with a smooth lattice consisting of subequal, circular to elliptical pores with subregular arrangement; basal mouth of thorax incomplete, subtriangular in section, not constricted, in a few tests with short, tooth-like, terminal spines. The three feet broadly splayed, each with sharp outward convexity; distally, they point downward; proximally, they extend downward at a low angle from the horizontal. Because the thoracic lattice is developed between the feet, the feet arise terminally instead of above the mouth of the thorax. Four relatively large collar pores; collar ring, which consists of the apical-lateral arches and the ventral arch, is represented by indistinct ribs occupying the stricture between cephalis and thorax.

Measurements; based on 6 specimens from stations 106, 133, 136, and 151: length of cephalis 16-21 µm, of thorax 27-39 µm; breadth of cephalis 16-23 µm, of thorax 52-91 µm; length of apical spine 31-46 µm; of vertical spine 0-15 µm, of feet 37-68 µm.

Remarks. The differences between this species and Diçtyophimus graciljpes Bailey were discussed in the remarks concerning the latter species. The size of this species including the feet and apical and vertical spines is smaller than D. gracilipes; the range in breadth of the thorax of this species is also greater than in D. gracilipes. A few specimens were observed with a nearly poreless cephalis and thorax (nearly hyaline).

Distribution. This species occurs more rarely in the Gulf than D. gracilipes. Its greatest frequency was observed at station 106. It has a slightly greater frequency at stations located within the diatomite facies, particularly, stations 106, 115, 133, 136, and 151. It is absent at all stations north of 151. It is very rare in the southern Gulf; therefore, its higher frequency in the northern Gulf may be explained by upwelling.
Haeckel (1887, p. 1198) reported this species from the Atlantic Ocean near the Canary Islands. D. brandtii Haeckel, which may be conspecific with this species, was reported from the north Pacific (loc. cit.). Because D. platycephalus has not been reported from high latitudes it is apparently a tropical to temperate species, present in all oceans.
Benson 1966


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