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Hexacontium pachydermum Jørgensen, 1900

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Hexacontium pachydermum:
The byspines on the outer shell vary considerably in length. They are found in all corners where the pores meet, so that each pore is surrounded by several byspines (generally 5 or 6). The pores on the outer shell are more or less round, the intermediate walls being on the whole broader than in the preceding species (Hexacontium enthacanthum), answering to the development of the outer shell which is altogether stronger in this species. This shell is especially thick. The length of the main spines varies considerably. The byspines on the middle shell are little conspicuous, and may be easy overlooked (as in the case of the preceding species, H. enthacanthum). The innermost shell is here seen less clearly than in H. enthacanthum, unless the thicker outer shell be removed. One may, therefore, easily mistake this species for a Hexalonche, by overlooking the inside ball. I have, however, repeatedly convinced myself on breaking the outer shells, that it is always present. Its construction is the same as in the preceding species.

No important difference in dimensions between this species and the preceding one seems to be found, and this is a very important factor when considering the question as to whether these supposed species are specifically different, or only constitute different forms of one of the same species. Here too the outer shell varies in size, but the middle and inmost ones are remarkably uniform in this respect and resemble those of H. enthacanthum. The ocean forms, however, appear to diverge essentially. I have not had an opportunity, though, of studying them more thoroughly in richer material, so that I cannot yet give a definite opinion as to the probability of separating new species. This, however, does not seem unlikely. For such a strong developed ocean form from the sea beyond Söndmöre (in February 1901, S/S Michael Sars, a sample kindly given to me by Dr. Gran) was found.

Strong, long main spines (most of the broken off). Numerous byspines (4-6 round each pore), long, needle shaped, 40µ long (nearly 4/5 of the radius of the outer shell). Outer shell very thickwalled (6-7µ thick), pores almost even, +/-8µ, very broadwalled, round, a little broader than the walls. 7 main spines, much narrower between the outer shells than outside the outmost one. The diameter of the three balls 108, 39, 19µ.

Occurred like the preceding species rather rarely and sparsely in deep water samples, though perhaps somewhat more frequently. As a rule it is found in deep water samples from such outer places where the sea water has easy access. During the spring diatom inflow, it seem generally toe be absent, except at greater depths in the inner fiords, where scattered specimens occur. This also seems to be the case, on the whole, with regard to the other Spumellaria.

Chiefly the same as in the preceding species [Hexacontium enthacanthum], often found together with it.

[Temperate oceanic form, which with us is only found in deep water, especially at a depth of 300m or more. Somewhat more frequent on the west coast of Norway. Also known from scattered spots in the sea beyond the coast of Norway and from the Faeroe and Shetland Isles northwards.]











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