| Home> Cenozoic> Holocene (Recent)> Nordic Seas>
 

List species

Lithomelissa hystrix J°rgensen, 1900

Description - Add description

Lithomelissa hystrix:
Cephalis not very high, finally, by the development of secondary, outer arches in the region of the neck, a broad semisphere, which is half of it sunk into the thorax.

The thorax is above campanulate, below cylindrical, with two distinct, lateral indentations in the upper part.

In the region of the neck in younger individuals, there are large holes, which later on are, to some extent, closed, by the development of outer arches between the lower part of the cephalis and the upper part of the thorax. The pores outside this region of the neck are roundish, of very varying size, being smallest on the upper part of the cephalis.

On the whole, there appears to be the same spines as in L. setosa, but fewer really protruding ones from the inner skeleton. The thorax here too appears to be similarly formed to that of L. setosa, from strong, obliquely downwards pointing byspines on the primary arches. A number of such obliquely protruding byspines are also seen in this species in the region of the neck. In addition, there are also numerous, needle-shaped byspines on the cephalis and the upper part of the thorax, and these, on a broad part of the shell, between the cephalis and thorax, develop fine, connecting beams, covering the large neck openings.

The region of the neck will here, in this way, be surrounded by a covering which causes the cephalis finally to be half (or wholly?) sunk into the thorax. This outer covering is chiefly formed from byspines on secondary arches.

Cephalis 22Ám broad, thorax 45-50Ám broad. The height of the thorax in the forms occurring in my material 34-40Ám. In these forms, which most probably were not fully developed, the brim of the thorax was provided beneath with short irregular spines, which no doubt are the walls of meshes in process of development.

It is a question whether this species should not be more correctly separated from the genus Lithomelissa. But as I have not as yet had an opportunity of studying the inner skeleton more carefully, I will, for the present, retain it in the genus in which I originally placed it.

Very rare and occurs only sparsely: 19/1-1899, 40 miles NW of GaukvŠr°, 0-700 m; 28/3-1899, the Tys Fiord I, 0-700 m.

Distribution: Also very rare on the west coast of Norway.
J°rgensen 1905


Description

 

Images

 

Synonyms

 

References

 

Distribution

 

Discussion / Comments

 

Web links