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Lithomelissa pentacantha (Popofsky, 1913)

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Benson, 1966, p. 363-366; pl. 24, figs. 6-9:

Lithomelissa hystrix J°rgensen

Lithomelissa hystrix J°rgensen, 1900, Bergens Mus. Aarbog (1899), p. 83; 1905, Bergens Mus. Skrifter, p. 136, Pl. 16, fig. 85.
Litomelissa [sic.] sp., Petrushevskaya, 1962, Zool. Zhurnal, vol. 41, p. 334, fig. 4.

Test consisting of a relatively large, smooth to spiny, ovoid to subspherical cephalis separated from a subcylindrica1, relatively smooth thorax by a distinct collar stricture which is covered by an irregular neck lattice developed between the three basal spines and thorax and the cephalis. Mouth of thorax not constricted; terminal margin incomplete. Pores of the cephalis subcircular to elliptical, relatively small, of unequal size, with subregular to irregular arrangement; upper surface of cephalis generally smooth, nearly hyaline in several specimens; two to three large dorsal sagittal pores are present on each side of the straight, nearly vertical apical bar of the cephalis. Pores of the thorax slightly larger than cephalic pores, subequal, subcircular to subpolygonal, subregularly arranged; those of the proximal portion of the thorax immediately below the collar stricture are slightly larger. The dorsal and primary lateral bars pierce the wall of the thorax and extend as three-bladed spines; the latter are nearly horizontal and pierce the thoracic wall at a higher level than the descending dorsal spine. A relatively heavy, three-bladed apical spine or horn extends from and is generally collinear with the apical bar of the cephalis. A short, thorn-like vertical spine originates from the ventral arch at the collar stricture. A few specimens have one or two accessory cephalic spines, similar to the apical spine; in a few specimens one or two accessory, three-bladed spines originate from the collar ring and extend nearly horizontally. In most specimens three collar pores are present, the vertical bar being absent; cardinal pores are of type B and appear in dorsal views (Pl. 24, fig. 9) as the lowermost pair of dorsal cephalic pores. In a few specimens a very thin or rudimentary vertical bar is present; this feature is of secondary importance in this species.

Measurements; based on 30 specimens from stations 106 and 192: length of cephalis 23-53 Ám, of thorax 30-62 Ám; breadth of cephalis 31-49 Ám, of external neck lattice 54-68 Ám, of thorax 38-77 Ám; length of apical spine 15-62 Ám, of vertical spine 7-16 Ám, of primary basal spines 16-68 Ám.

Remarks. This species is distinguished from Lithomelissa thoracites Haeckel by the presence of large dorsal pores located on either side of the apical bar of the cephalis, the general absence of the vertical bar, and the presence of an external irregular lattice covering the neck region. This species is identical with Lithomelissa hystrix J°rgensen.
Not all specimens have the neck lattice completely developed. If they have large dorsal cephalic pores, they were identified with this species; if not, they were identified as Lithomelissa thoracites Haeckel.

Distribution. This species is common at all stations where it is present in the northern half of the Gulf and is abundant at station 133. In the southern Gulf it is common at the offshore stations 81, 92, and 93 and rare at the others, thus indicating its preference for more nearly oceanic waters in this region. It is absent at the marginal stations 90, 130, 194, 203, and 214. At stations 115, 133, and 136 it is the most abundant species having frequencies of 5.6%, 11.6%, and 6.6%, respectively. It is the second most abundant species at stations 151 (6.4%) and 208 (9.3%) and the fourth most abundant species at stations 191 (5.6%) and 192 (6.45). Its high frequency at these stations which are located in the diatomite facies indicates its response to upwelling there.
J°rgensen (1905, p. 136) states that Lithomelissa hystrix occurs sparsely and very rarely off the Norwegian coast and in the Tys Fjord at water depths ranging between 0 and 700 meters. Petrushevskaya (1962) reports Litomelissa[sic.] sp. from a sediment sample from the eastern Pacific near California. This species, therefore, is cosmopolitan, occurring at high as well as low latitudes.
Benson 1966
Benson, Benson, 1966, p. 353-355; pl. 23, figs. 18-20:

Plectacantha oikiskos J°rgensen

Plectacantha oikiskos J°rgensen, 1905, Bergens Mus. Skrifter, pp. 131-132, Pl. 13, figs. 50-57; Bernstein, 1932, Archiv fŘr Protistenkunde, vol. 76, p. 221, Pl. 3, figs. 2,3.
Periplecta intricata (Cl.) J°rgensen, 1900, Bergens Mus. Aarbog (1899), pp. 73-75.
Test consisting of a small, globular to subspherical cephalis, without a thorax but in many tests with an outer, irregular lattice completely surrounding the cephalis (Pl. 23, fig . 20). Three collar pores present, the vertical bar not observed, but may be present in some tests; cardinal pores of type B. [See pp. 99-101, text-figs. 7 and 8, and pp. 114-115 for description of types A and B] Two to three pairs of large, dorsal, sagittal cephalic pores are separated by the straight apical bar which extends as a straight, conical to three-bladed apical spine of variable length. A short vertical spine arises from the ventral arch. Remaining pores of cephalis unequal, with irregular shape and arrangement. Surface of cephalis generally with spines which in many specimens are branched distally forming a portion of the outer latticed covering. Primary lateral and dorsal spines relatively long, curve downward or are straight but diverge downward from the collar ring; they are generally conical as is the apical spine, but the latter as well as the basal spine are heavy and three-bladcd in a few specimens. Outer lattice surrounding cephalis with irregular surface and pores; subcircular in transverse section.

Measurements; based on 20 specimens from stations 191 and 192: length of cephalis 31-49 Ám, breadth 28-43 Ám; breadth of outer lattice 49-74 Ám; length of apical spine 15-57 Ám, of dorsal and primary lateral spines 12-65 Ám.

Remarks. The smaller, generally irregular cephalis and lack of any structures suggestive of a thorax distinguish this species from incompletely developed specimens of Lithomelissa hystrix from the Gulf. The presence of the 2-3 pairs of 1arge, dorsal sagittal
cephalic pores, the non-ovoid shape of the cephalis, and the presence of an outer lattice surrounding the whole cephalis, not just its neck region, distinguish this species from Peridium longispinum J°rgensen.
Although the short vertical spine is present, the vertical bar is absent; therefore, this species conforms to J°rgensen's definition of the genus Plectacantha (1905, p. 131). The vertical bar may be present, but most specimens are not favorably oriented for this to be observed. All specimens studied in slides were not observed with this structure.

Distribution. This species is very rare in the southern half of the Gulf, occurring only at stations 27, 34, 56, 60, 81, and 93. It has a much greater frequency in the northern Gulf. In this region it is absent at stations 130, 194, 203, and 214; it is common at stations 133 and 192, abundant at station 191, and rare at the others where it is present. Its highest frequency in the Gulf occurs in the northernmost diatomite facies at stations 191 where it is the most abundant species (21.6%) and 192 where it is the third most abundant species (7.4%). Its large increase in frequency at these stations is undoubtedly the result of its response to the upwelling that accounts for high diatom production here.
J°rgensen (1905, p. 132) states that Plectacantha oikiskos is rare from waters off the west coast of Norway and is probably a boreal oceanic species. Bernstein, (1932, p. 221) reports the same species from the Barents, Kara, and Queen Victoria Seas.
Benson 1966
Benson, 1983, p. 506:

Plectacantha oikiskos J°rgensen

Remarks. In the Gulf of California, this species(?) may represent tests of Lithomelissa hystrix with the thorax undeveloped.
Benson 1983


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