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Lithomelissa thoracites Haeckel, 1862

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Shell smooth, with deep collar stricture. Cephalis ovate, with two divergent, slender, conical horns, of about half the length; a major oblique occipital horn on the posterior face, and a minor, nearly horizontal horn above the collar stricture, on the anterior face. Thorax about as large as the cephalis, truncate, ovate. Pores of both joints irregular, roundish, of different sizes. From the upper half of the thorax, below the collar stricture, there arise three slender, conical divergent feet, about as long as the cephalis. Mouth truncate, wide open, not constricted. On the numerous varieties of this common species compare my Monograph, on the structure of the ovate central capsule (enclosed in the cephalis), Hertwig, loc. cit.

Cephalis - 0.05 to 0.06 long, 0.04 to 0.05 broad; thorax 0.03 to 0.05 long, 0.05 to 0-07 broad.
Haeckel 1887
Lithomelissa thoracites:
Schale glatt mit tiefer halseinschnürung. Cephalis eiförmig mit zwei divergierenden, konischen hörnern (D und V), von denen das obere (D) länger und schräg nach oben gerichtet ist, während das zweite kürzere die schale dicht oberhalb der halseinschnürung durchbohrt und fast wagerecht verläuft.

Thorax so hoch wie die cephalis, abgestutzt eiförmig. Poren beider schalenabschnitte unregelmässig, rundlich und von verschiedener grösse. Von der oberen hälfte des thorax entspringen die schräg abwärts gerichteten stacheln D, Lr und Ll. Die schalenmündung ist weit offen und nicht verengt.

Cephalis 0.05-0.60mm hoch, 0.040-0.050mm breit; Thorax 0.030 bis 0.050mm hoch, 0.050-0.070mm breit.
Schröder 1914
Benson, 1966, p. 366-369; pl. 24, figs. 10-12, not 13:

Lithomelissa thoracites Hacekel

Lithomelissa thoracites Haeckel, 1862, Die Radiolarien, p. 301, Pl. 6, figs. 2-8; Hertwig, 1879, Der Organismus der Radiolarien, p. 204, Pl. 8, fig. 1; Popofsky 1913, Deutsche Südpolar-Exped., vol. 14, pp. 337-338, text figs. 44-47.
Litomelissa[sic.] thoracites Haeckel, Petrushevskaya, 1962, Zool. Zhurnal, vol. 41, pp. 332-333, figs. 2,3.
?Lithomelissa monoceras Popofsky, 1913, Deutsche Südpolar-Exped., vol. 14, p. 335, Pl. 32, fig. 7; text fig. 43.

Test similar to that of Lithomelissa hystrix but generally with smoother surface and without an external neck lattice. Large dorsal cephalic pores on either side of the apical bar absent, replaced by pores similar in size to those of the remainder of the cephalis. Pores of the cephalis circular to subcircular, relatively small, subequal, subregularly arranged; those of the thorax similar but slightly larger and with a less regular arrangement. The apical, vertical, dorsal, and primary lateral spines similar to those of L. hystrix, although conical instead of three-bladed in a few specimens. Collar ring generally with four collar pores; the vertical bar is present in most tests but is thin and apparently secondary; cardinal pores are of type B. In a few specimens the cephalis is ovoid, smooth, nearly hyaline, and the thorax is reduced in size.

Measurements; based on 30 specimens from stations 106 and 192: length of cepha1is 37-69 µm, of thorax 31-62 µm; breadth of cephalis 38-71 µm, of thorax 57-81 µm; length of apical spine 0-55 µm, of vertical spine 2-8 µm, of dorsal and primary lateral spines 11-62 µm.

Remarks. Specimens of this species from the Gulf agree well with Petrushevskaya’s (1962, figs. 2, 3) and Popofsky’s (1913, text figs. 44-47) illustrations of Lithomelissa thoracites Haeckel. They differ from Haeckel’s (1887, p. 1206) and Hertwig’s (1879) description in that the three basal spines and the apical spine are not always conical; they are generally three-bladed.

A few specimens of this species have one or two arched bars developed between the cephalis and thorax, suggestive of a neck lattice; however, the lack of large dorsal cephalic pores on either side of the apica1 bar distinguishes these forms from Lithomelissa hystrix Jørgensen. This species and L. thoracites are very similar, and the distinction between the two is not always clear. Several species of the genus Lithomelissa are very similar to these two species. Restudy of this group might lead to a reduction in the number of species.

Several specimens conforming to Lithomelissa monoceras Popofsky were tentatively identified as L. thoracites. These tests are very smooth, and the upper part of the cephalis is nearly hyaline (Pl. 24, fig. 13). The rare occurrence of these forms makes it impossible to study their complete range of variation. It is the writer's opinion that they are variant forms of L. thoracites in the Gulf, but further study is necessary before they can be placed positively in synonymy with this species.

Distribution. The distribution of this species in the Gulf is similar to that of Lithomelissa hystrix except that it is less abundant. It is cosmopolitan in the Gulf, being absent at stations 130, 203, and 214. In the southern half of the Gulf its frequency is slightly greater than that of L. hystrix; it is rare at all stations except 34 and 93 where it is common. It is nearly common at station 64 indicating its possible response to upwelling in this region. In the northern Gulf it is rare except at stations 136, 151, 191, and 192 where it is common. At the latter two stations it is the second most abundant species (7.6%). As in L. hystrix its greater frequency in the northern Gulf is associated with upwelling in this region.

Haeckel (1887, p. 1206) states that Lithomelissa thoracites occurs at the surface in all oceans including the Mediterranean Sea. Popofsky (1913, p. 338) reported the same species from the western tropical part of the Indian Ocean and from the tropica1 South Atlantic. He also reported L. monoceras Popofsky (op. cit., p. 335) from the same regions. Petrushevskaya (1962) reported L. thoracites from the eastern Pacific near California and in the northwestern Pacific at a water depth of 100-200 meters. The apparent absence of this species from high latitudes indicates that it is a tropical to temperate species present in all oceans.
Benson 1966


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