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Lithomelissa setosa Jørgensen, 1900

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Lithomelissa:
The four primary spines, A, D, Lr and Ll, are present, as well as the ventral, sagittal one.

The apical spine, D, runs in the wall of the cephalis, and protrudes like a needle-shaped tophorn, the lower part being inside the lattice shell. The dorsal, basal spine, A, protrudes obliquely like a simple spike (needle), rather far down on the thorax. On the inside, it is propped up against the shell by arch-shaped supporting beams (corresponding to the apical arches in Phormacantha hystrix). The lateral spines pierce the thorax in its upper part and protrude each of them as (one or?) two spikes.

The ventral, sagittal spine protrudes near the region of the neck (between cephalis and thorax), and is, in Lithomelissa setosa, connected to the right lateral spine, Ll, by an inner little lattice-plate, whilst it is farther distant from the left, lateral spine. In other words, it divides the angle between the lateral spines into two very uneven parts, one small one to the right, and a larger one to the left. By this feature, young forms of Lithomelissa setosa are easily recognized, even if only the cephalis be developed.

The primary arches between D, Lr and Ll are well developed, and protrude on the inside like three archshaped ledges, running upwards. By means of outwards and downwards bent byspines from these primary arches, together with branches and arches from the dorsa spine, A, and the lateral ones, the thorax is developed. In the upper part of the thorax, there are, therefore, formed three, more or less distinct swellings, a right one, below the primary, right, lateral arch, a left one, below the left, lateral arch, and a ventral one, below the primary, ventral arch.

Here too, as in all the forms of Cyrtoidea occurring in my material, there is an inner axial spine, pointing downwards vertically from the ventral end of the central rod, thus having the same starting point as the ventral, sagittal spine.

Lithomelissa setosa:
Jørgensen L. 91 (=Jørgensen 1900), p. 91, non Botryopyle setosa CL. L. 30 (=Cleve 1899), p. 27, pl. 1, f. 10.
Compare above the description of the genus and of the structure of the species in the introduction to the group Nassellaria. Cfr. too Jørgensen (1900) where a detailed description will be found.

Of byspines, there are usually too strongly developed one on the right, lateral arch, protruding in the form of simple spikes in the upper part of the thorax, one or two similar ones on the left, lateral arch, and a couple on the cephalis.

The spikes, which are seen in varying numbers and differently developed on the lower margin of the thorax are – at any rate most often – temporary formations. They disappear later on as the development of the thorax progresses, the meshes being formed between these spines. It is possible that var. belonophora Jørgensen (1900, pl. 4, fig. 22) is the fully developed form, and that its marginal spines are therefore permanent.

Frequent, mostly in deep water samples, sometimes – but rarely – in the surface. Rarely at all numerous.

Distribution: Belongs to the most frequent Radiolaria on the west coast of Norway.
Jørgensen 1905


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