“Rossella antarctica, nov. gen. P1. XXI.
Large peripheral spicule with quaternate or cruciform head, consisting of four arms radiating at more or less than right angles from the peripheral end of a vertical shaft (Pl. XXI. fig. 1); arms very long, spreading, somewhat sigmoid in their course (fig. 6), round, ending in attenuated extremities, covered throughout with a layer of microspines in close approximation, and here and there large or macrospines, all directed outwards (figs. 1, a, b, and 4, c, d), the latter failing towards each end of the arm; shaft also sharp-pointed, and covered with the layer of microspines, but not so distinct, and entirely without macrospines (fig. 1, d, c); so that, under a low power, the arms appear spined and the shaft smooth.
Podal spicule consisting of a long shaft with anchor-head composed of four recurved arms (fig. 7) and sometimes a fifth, which is in continuation with the shaft, and thus renders the spicule hexactinellid (fig. 8, a). Peripheral and podal spicules both visible to the unassisted eye, the largest of the former presenting a shaft about 4 ½ -12ths and each of the arms about 3-12ths of an inch long (figs. 5 & 6). Head of podal spicule 1-20th of an inch broad, and longest fragment of shaft, with head attached, 1 ½ inch (fig. 10). From the latter having become attenuated towards the broken end, it is probable that, if entire, it would not have exceeded two inches. Length of podal spicule, generally, unknown.
Hab. Marine. Deep sea, in 206 to 300 fathoms.
Loc. Antarctic Ocean, in lat. 74 ½° to 77 ½° S and long. 175° W.
Obs. All that I have to offer respecting this sponge is the description of these two forms of spicules. It might seem strange that I should endeavour to establish a new genus upon them, were it not considered that the four-armed anchor-head (fig. 7) is unique, so far as our acquaintance with the Spongiadæ at present goes; that is to say, with the exception of Acarnus innominatus, Gray, where there is a fourth arm, but in a totally different kind of spicule (Annals, 1871, vol. vii. p. 273, pl. 17), I know of no other instance. Secondly, the four-armed, spreading, or great peripheral spicule (fig. 1) is so far identical with that of Carteria and Holtenia, but totally differs from it in being spiniferous instead of smooth. Perhaps the minute cruciform-headed and spined spicules congregated in multitudes along the course of the smooth arms in Carteria and Holtenia may be represented by the spines on those of Rossella. The only question, therefore, is, whether the two spicules belong to the same sponge or to two different sponges; and this seems to be answered by the facts that the two forms are analogous to the anchor-head or anchoring spicule and the great cruciform one of Holtenia respectively, and also that both forms are equally and abundantly present about the fragments of Tethya antarctica, wherein they have become entangled, to the exclusion of every other kind, except those which belong to the Tethya itself. Thus we may fairly assume that they both belonged to some deep-sea sponge which, thus differing from all others yet known, merits a separate genus, with perhaps no more appropriate name than that of " Rossella," after the great navigator who dredged them up from the bottom of the Antarctic Ocean.
It is impossible to say how long the shafts of the anchor-headed spicules might have been, although the longest portion that I have found is attenuated at the fractured end; for, although this generally indicates an approaching termination, still the attenuation may or may not be much prolonged. But, judging from the average of specimens found, I should say, as before stated, that the shaft probably did not exceed two inches.
The occurrence of a fifth arm in the direction of the shaft, forming a kind of spike at the end (fig. 8), seems to be too common to be abnormal, and therefore allies this sponge still more to the Hexactinellidæ of Schmidt.
I also found one of these six-armed spicules in which there is an extension of one of the recurved arms to such a degree as to be almost equal in size and length to the shaft (fig. 9, a). This, I fancy, must, be an abnormal form.
In no portions of Tethya antarctica that I mounted in Canada balsam, nor in any others examined, could I find the least trace of any of the minute kinds of spicules which characterize the Hexactinellidæ. Then it must be remembered that, although the large spicules of a sponge of this kind might be caught up and preserved by such a “tangle” as the Tethya afforded, the small spicules to which I allude would inevitably escape.
Fig. 3 is a more magnified view of the central portion of one of the great cruciform peripheral spicules, here introduced for comparison with the fossil fragment (Annals, 1871, vol. vii. p. 126, pl. ix. fig. 37). It is the only part of this spicule which in the hurly-burly of the waves and currents, would be likely to survive all the rest on its way to become fossilized; and the identity is so great that my conjecture, at the page mentioned, of their having belonged to a “quaternate or quadrifid system, whose parallel is only to be found in Hyalonema (Carteria)&c." is thus confirmed. That which I supposed to be an enlarged central canal in the fossil is the original shaft, and the external portion (d) an additional layer, as evidenced by the recent specimen—thus being only an instance of the common mode of strengthening and enlarging the structures of the Spongiadæ, viz. by the addition of layers to the external surface of the horny or silicified fibre.
Hence, having found fossilized fragments of this system in the Greensand, the Hexactinellidæ cannot be descended from the Ventriculitidæ of the Chalk, as Schmidt's pedigree-table (Atlant. Spong. Faun. 1870, p. 83) would have it, in support of the evolution-theory. But as a "theory" is but a “theory” it is only to correct the mistake and maintain the remaining part until another error is found out, and so on.
I take this opportunity of stating, in modification of what I have said in my “Fossil Sponge-spicules of the Greensand,” p. 126 (op. et loc. cit.), viz. that I had not been able to find any hexradiate spicules in my mounted specimens of Hyalonema, that since then I have obtained and mounted other specimens from an undoubted Hyalonema, taken off with my own hands, in which hexradiate spicules, of minute size, are as plentiful as in any other sponge of the kind. Still I maintain that, if Hyalonema is to be considered one of the Hexactinellidæ, it must be based upon the presence of these small hexactinellid spicules; for the large ones of the periphery, and the minute feathered ones too, there, which appear to be the same in this respect as in Holtenia, bear no trace of the sixth ray, that I can see. Indeed the sixth ray, if on one of these large cruciform peripheral spicules, which appear to be intended to bind down the surface smoothly, would, by its projecting outwards, be evidently out of place; and if these spicules are to be considered hexradiate because a little projection of the central canal may be observed where the sixth ray would be if developed, to carry out this principle in the Spongiadæ will be found very inconvenient, if not wholly impracticable. In distinguishing species, which is a purely conventional arrangement, we should select, if possible, prominent features that are easily recognizable, both for practical purposes and to facilitate the study of natural history, there being, comparatively, no limit to minute distinctions, as there is no real line of demarcation in nature, if we do not limit the power to which the microscope should be used in this respect. The infinite mind of Nature does not require them; but the finite mind of man cannot get on without this aid, and still less the “finite purse;” when the more costly, i.e. the highest, powers of the microscope are required for their detection.”
(Carter, 1874)
