The sandy shells are a very interesting series. In Astrorhiza the sand grains are loosely agglutinated, without mineral cement; they leave numerous pores for the exit of the protoplasm, and there are no true pylomes. In other forms the union of the grains by a calcareous or ferruginous cement necessitates the existence of distinct pylomes. Many of the species reproduce the varieties of form found in calcareous tests; some are finely perforated, others not. Many of the larger ones have their walls thickened internally and traversed by complex passages; this structure is called labyrinthic (fig. 19, g, h). The shell of Endothyra, a form only known to us by its abundance in Carboniferous and Triassic strata, is largely composed of calcite and is sometimes perforated.
| Fig. 15.—Cycloclypeus. |
It is noteworthy that though of similar habitat each species selects its own size or sort of sand, some utilizing the siliceous spicules of sponges. Despite the roughness of the materials, they are often so laid as to yield a perfectly smooth inner wall; and sometimes the outer wall may be as simple. As we can find no record of a deflected stylopyle to the primitive chamber of the polythalamous Arenacea, it is safe to conclude that they have no close alliance with the Porcellanea.
Classification.
I. Nuda.—Protoplasmic body without any pellicle or shell save in the resting encysted condition, sometimes forming colonial aggregates by coalescence of pseudopods (Myxodictyum), or even plasmodia (Protomyxa). Brood cells at first uniflagellate or amoeboid from birth. Fresh-water and marine genera Protogenes (Haeckel), Biomyxa (Leidy), Myxodictyum (Haeckel), Protomyxa (Haeckel) (fig. 1B).
This group of very simple forms includes many of Haeckel’s Monera, defined as “cytodes,” masses of protoplasm without a nucleus. A nucleus (or nuclei) has, however, been demonstrated by improved methods of staining in so many that it is probable that this distinction will fall to the ground.
| Fig. 16.—Heterostegina. |
II. Allogromidiaceae (figs. 1A, 2).—Protoplasmic body protected in adult state by an imperforate test with one or two openings (pylomes) for the exit of the stylopod; test simple, gelatinous, membranous, sometimes incrusted with foreign bodies, never calcareous nor arenaceous; reproduction by fission alone known. Fresh-water or marine genera Allogromia (Rhumbl.), Myxotheca (Schaud.), Lieberkühnia (Cl. & L.) (fig. 1A), Shepheardella (Siddall) (fig. 2, 3-10), Diplophrys (Barker), Amphitrema (Arch.) (fig. 2, 11), Diaphorophodon (Arch.) (fig. 2, 12), are possibly Filosa. This group differs from the preceding in its simple test, but, like it, includes many fresh-water species, which possess contractile vacuoles.
III. Astrorhizidiaceae.—Simple forms, rarely polythalamous (some Rhabdamminidae), but often branching or radiate; test arenaceous, loosely compacted and traversed by chinks for pseudopodia (Astrorhizidae), or dense, and opening by one or more terminal pylomes at ends of branches. Marine, 4 Fam. The test of some Astrorhizidae is so loose that it falls to pieces when taken out of water. Haliphysema is remarkable for its history in relation to the “gastraea theory.” Pilulina has a neat globular shell of sponge-spicules and fine sand. Genera, Astrorhiza (Sandahl) (fig. 22), Pilulina (Carptr.) (fig. 19), Saccammina (Sars) (fig. 19), Rhabdammina (Sars), Botellina (Carptr.), Haliphysema (Bowerbank) (fig. 22).
IV. Lituolidaceae.—Shell arenaceous, usually fine-grained, definite and often polythalamic, recalling in structure calcareous forms. Lituola (Lamk.) (fig. 19), Endothyra (Phil.), Ammodiscus (Reuss), Loftusia (Brady), Haplophragmium (Reuss) (fig. 22), Thurammina (Brady) (fig. 22).
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| Modified from F. Schaudinn, in Lang’s Zoologie. | |
| Fig. 17.—Life Cycle of Polystomella crispa. | |
A, Young megalospheric individual. B, Adult decalcified. C, Later stage, resolving itself into two flagellate gametes. D, Conjugation. E, Microspheric individual produced from zygote. | F, The same resolved itself into pseudopodiospores which are growing into new megalospheric individuals. 1, Principal nucleus, and 2, subsidiary nuclei of megalospheric form. 3, Nuclei. 4, Nuclei in multiple division. 5, Chromidia derived from 4. |