The legion Phæodaria, or Cannopylea, in the extent here defined, was constituted by me in 1878, in my Protistenreich (p. 102) under the name Pansolenia. This name was given on the supposition that the skeleton of these interesting Radiolaria is always composed of hollow tubules, in contrast to that of the other Radiolaria, where it is never tubular. But I was soon convinced that this supposition was erroneous, that in a great part of the Pansolenia the skeleton is not composed of hollow tubules but of solid bars, and that a constant, very characteristic, and never failing mark of this group is to be found in the peculiar phæodium, a voluminous, constant, extracapsular pigment body. Therefore, in 1879, I changed the name into Phæodaria, and having discovered in the collection of the Challenger an astonishing number of new and wonderful types of this group, I described, in a preliminary note on it, four different orders and ten families with thirty-eight genera (Ueber die Phæodarien, eine neue Gruppe kieselschaliger mariner Rhizopoden; in Sitzungsberichte der Jenaischen Gesellschaft für Medicin und Naturwissenschaft. Sitzung vom 12th December 1879).
In the same year (1879), Richard Hertwig, in his excellent work entitled Der Organismus der Radiolarien, published the first accurate description of the intimate structure of the soft body of the Pansolenia, and mainly of their central capsule; and having always observed, in the few representatives examined by him, three openings in the capsule (one main-opening and two accessory openings), he called them Tripylea (loc. cit. p. 87), being guided by the erroneous supposition that these three openings are constant in all members of the group. But this is by no means the case. The two accessory openings are completely absent in several families, whilst in others their number is increased. A constant and very striking character, however, of all Phæodaria, is the peculiar structure of their tubular main-opening, which I call astropyle, with its radiate operculum and cannular proboscis. On account of this important and startling characteristic I proposed in 1881 to call this group Cannopylea. The two names Phæodaria and Cannopylea both express a very striking and quite constant character of these curious Radiolaria, whilst the two names Pansolenia and Tripylea are applicable only to a part of the whole legion.
The history of our knowledge of the Phæodaria is short, but very remarkable. Although hundreds of species, many of them cosmopolitan, are distributed over all oceans and all zones, although their size is in general much greater than that of the other Radiolaria (usually 1 to 2 mm., often even 5 to 10 mm. or more), and although their form and structure are usually striking, nevertheless the Phæodaria remained completely unknown up to the year 1859. During that year I observed the first forms living in the Gulf of Messina, and described and figured in 1862 in my Monograph five genera and seven species, viz., (1) Aulacantha scolymantha (p. 263), (2) Thalassoplancta cavispicula (p. 261, now Cannobelos cavispicula), (3) Aulosphæra trigonopa, and Aulosphæra elegantissima (p. 359), (4) Spongodictyum trigonizon (p. 459, now Sagoplegma trigonizon), and (5) Cœlodendrum ramosissimum, and Cœlodendrum gracillimum (p. 361). I recognised the structure of the three genera enumerated as 1, 3, and 5, as so remarkable and so different from that of the other Radiolaria, that I founded three peculiar families for them, the Aulacanthida, Aulosphærida, and Cœlodendrida.
The first note on the numerous remarkable Phæodaria discovered by the Challenger, and mainly on the large-sized inhabitants of the deep-sea, was published in 1876 by Dr. John Murray, in his Preliminary Reports on Work done on Board the Challenger (Proc. Roy. Soc., vol. xxiv., read March 16, 1876). He pointed out (loc. cit., p. 535), that the tow-nets, sent down to a great depth (according to a new plan, adopted in April 1875) brought up on every occasion a great many new and peculiar Rhizopods, which had never been observed in the nets used near the surface. "The shells of all have an exceedingly beautiful tracery, a fenestrated appearance often, which a closer examination shows to be caused by pit-like depressions. Some have only one, others have several openings, through which the sarcode flows. The sarcode of all these deep-sea Rhizopods has many large black-brown pigment-cells. At times they come up with a good deal of the sarcode outside of the shell; and two specimens have been seen to throw out elongated pseudopodia" (loc. cit., p. 536). Dr. John Murray distinguished at that time not less than fifty species of these interesting deep-sea Rhizopods and called them provisionally Challengerida; a term which we retain here for the largest and most characteristic family. He gave at the same time, in an accompanying plate (xxiv.), six figures of new Phæodaria, the names of which (as found by me in 1879 in the corresponding preparations) are the following; (1) Challengeria naresii, (2) Challengeria aldrichii, (3) Bivalva compressa (now = Conchopsis compressa), (4) Tuscarora belknapii, (5) Challengeria circopora (now = Circoporus sexfurcus), and (6) Haeckeliana porcellana. A great number of these Challengerida (twenty species) were afterwards figured by Dr. John Murray in the Narrative of the Cruise of H.M.S. Challenger, 1885, vol. i. part 1, p. 226, Pl. A; viz., fourteen species of Challengeria and six species of Tuscarora.
The most important advance in the knowledge which we had of the peculiar organisation of the Phæodaria, was made by the accurate description which Richard Hertwig published, in 1879, of the intimate structure of their central capsule, and mainly of its peculiar openings. He examined living at Messina the following three forms, described in my Monograph; (1) Aulacantha scolymantha, (2) Aulosphæra elegantissima, and (3) Cœlodendrum ramosissimum. Besides, he described an interesting new genus, Cœlacantha anchorata; and another new form, which he placed in the Aulosphærida, as Aulosphæra gracilis, but which really was a new genus of Sagosphærida, here described as Sagoscena gracilis. Finally, Hertwig first discovered that the peculiar bodies, described by Ehrenberg as Dictyocha and placed by him in the Diatomea (Polygastrica), were the isolated pieces of the skeleton of a true Phæodarium, and that they were scattered loosely in great numbers over the surface of the jelly-sphere, just as are the hollow spicula of Thalassoplancta or Cannobelos.
The six species mentioned, of which Hertwig gave a very accurate description and very instructive figures, belong to six different genera, and these represent six different families of Phæodaria, viz.; Aulacanthida, Aulosphærida, Cœlodendrida, Cannosphærida, Sagosphærida and Cannorrhaphida. He found that all these six forms, in spite of great differences in the form and structure of their skeleton, were identical in the structure of the central capsule; and since he observed constantly three openings in its double wall (a large main-opening on the oral pole, and a pair of lateral accessory openings on the aboral pole of its main axis) he called them Tripylea (loc. cit., p. 87, 94). But he also pointed out the remarkable shape of their voluminous extracapsular body, and especially the characteristic position, size, colour and composition of the large pigment body, which I had called the phæodium.
The accurate description of the gigantic and elegant skeleton of a new Phæodarium, surpassing all other known Radiolaria in its extraordinary size (15 mm.), was published in 1882 by O. Bütschli (in Zeitschr. f. wiss. Zool., vol. xxxvi. p. 486, Taf. xxxi.). He called it Cœlothamnus davidoffii, in honour of its discoverer, who had found it floating on the surface of the Gulf of Villafranca, near Nice. He placed it among the Cœlodendrida; it belongs, however, to that part of this group which possesses a nasal tube, and which I afterwards separated under the name Cœlographida.
The total number of Phæodaria, hitherto described and illustrated by figures, amounts therefore to seventeen species, viz., the seven species first described by myself (in 1862); the six new species figured by Dr. John Murray (in 1876); the three new species discovered by Hertwig (in 1879) and the single species last-mentioned described by Bütschli (in 1882). The rich collection of the Challenger has added to this small number such an astonishing wealth of new and remarkable forms, that I can describe in the following system of Phæodaria not less than eighty-four genera and four hundred and sixty-five species. These belong to fifteen different families and four different orders. But this great number is probably only a small part of the numerous interesting Phæodaria, which are abundantly distributed over all the oceans; those (e.g.) of the Indian and of the Arctic Oceans are almost unknown.
The great majority of these wonderful Phæodaria are inhabitants of the deep-sea, mainly of the southern hemisphere, and are so common in many stations explored by the Challenger, that its collection contains many thousands (or rather hundreds of thousands) of well-preserved specimens. A smaller part of the legion is found on the surface, widely distributed over all oceans; some of these are very common (as, e.g., Aulacantha, Aulosphæra, Sagosphæra, Cœlodendrum, Castanella, &c.) and it is difficult to explain how they could entirely escape the eyes of all former observers.
The three general characters which distinguish the Phæodaria easily and constantly from all the other Radiolaria are the following:—(1) the double membrane, a thick outer and a thin inner envelope, of the big central capsule; (2) its typical main-opening or astropyle, placed on the oral pole of the main axis, and distinguished by a peculiar radiate operculum, with tubular proboscis; (3) the phæodium, or the peculiar voluminous pigment-body, which constantly lies in the oral half of the calymma, surrounds the oral part of the central capsule, and is composed of numerous phæodella, or singular pigment-granules of green, olive, brown or black colour.