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Art. XXXIV.—Notes on a New Zealand Actinian, Bunodes aureoradiata.
[Read before the Wellington Philosophical Society, 3rd June, 1908.]
The family Bunodidæ was established by Gosse for the reception of forms “the surface of whose column is studded with persistent tubercles, and which is not provided with marginal spherules or with perforations of the integument.” Among other genera it included Tealia and Bunodes. The latter genus included one species, B. coronata, which was provided with acontia,* structures which are now recognised as denoting sagartiad affinities. Among the “Challenger” material Hertwig found a Bunodes (B. minuta) “whose structure approaches that of Sagartia more closely than that of Tealia.” Considering, therefore, that Bunodes and Tealia should be widely separated systematically, he placed the genus Bunodes among the sagartiads,† and established the family Tealidæ, taking T. crassicornis as its type. He made the presence of a strong endodermal sphincter muscle the leading characteristic of the family, also regarding of importance the presence of a large number of perfect mesenteries, and including forms with both smooth and warty columns. Later‡ he changed the name of the family, restoring the older name Bunodidæ.
Referring to Gosse's description of various species of Bunodes, we find the hexamerous condition to be constant, the tentacular formulæ being 6 + 6 + 12 + 24 = 48, 6 + 6 + 12 + 24 + 24 = 72, or 6 + 6 + 12 + 24 + 48 = 96. Again, in Delage and Herouard the number of mesenteries in Bunodes is stated to be 24 pairs, 12 of them being perfect. Gosse's description of T. crassicornis states the tentacular formula as 5 + 5 + 10 + 20 + 40 = 80. Again, Bourne§ gives the mesenterial arrangement of T. crassicornis as follows: 10 pairs complete and apparently primary, 10 pairs secondary, 20 pairs tertiary. There appears to be reasonable ground for thinking that the hexamerous and pentamerous forms should not be associated in the same family. Bourne separates them, and, “provisionally accepting” an ingenious suggestion made by Boveri in his “Development and Phylogeny of Zooantharia,” makes Tealiidæ one of his families in which the hexamerous arrangement is obscured by precocious development of the secondary and succeeding cycles of mesenteries.
In a paper (1901) which I have not seen, but which is referred to by Torrey,∥ McMurrich unites in a new family, Cribrinidæ, Ehrenberg's genus Cribrina, which he thinks synonymous with Bunodes (Gosse), Bunodactis (Verrill), and Evactis (Verrill). As I do not know his reasons for this change, I propose for the present to retain the older name of the family—namely, Bunodidæ.
Fam. Bunodidæ.
Tentacles digitate; pedal-disc present, acontia absent; sphincter strong, circumscribed, endodermal; numerous perfect mesenteries; column generally covered with warts.
[Footnote] * “Actinologia Britannica,” p. 204.
[Footnote] † “Challenger” Report, Zoology, vol. vi.
[Footnote] ‡ Supplement to “Challenger,” Report.
[Footnote] § “Treatise on Zoology,” ed. Ray Lan-kester.
[Footnote] ∥ Proc. Wash. Ac. Sc., vol. iv, p. 390.
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Genus Bunodes.
Bunodidæ with tubercles arranged in vertical series. Only the series corresponding to the mesenteries of the 1st cycle run the full length of the column. Marginal spherules on edge of disc. 24 pairs of mesenteries, 12 of them perfect, and all fertile except the directives.
Bunodes aureoradiata, n. sp.
Specific Character.—Yellow radii in 6 groups of 3.
Pedal-disc.—Adherent; slightly wider than the column; the edge undulate to correspond with the vertical rows of tubercles. On each undulation are 2 or sometimes 3 perforations, through which, when irritated, the animal projects nematocysts torpedo-fashion, and in such a manner as at first sight to suggest feeble acontia.
Column.—Cylindrical. In full expansion it is higher than the breadth. The lower half is light or yellowish-brown, upper half greenish-brown. There are 24 vertical rows of tubercles or verrucæ: near the bottom of the column these become mere markings; they increase in size as they ascend the column, culminating in a row of 24 white beads at the bases of the outer cycle of tentacles. The rows of tubercles correspond to the endocœles of the mesenteries; they consist of evaginations of the body-wall, and contain ectoderm, mesoglœa, and endoderm; they are perforated, and probably are able to act as suckers. The ectoderm of the column contains numerous nuclei, fairly regularly arranged. Cell outlines are indistinguishable in my preparations, but the nuclei are so arranged as to suggest that they belong to long narrow cells. The mesoglœa consists of fibres imbedded in a structureless vacuolated matrix, in which are also a few other immigrant cells from the ectoderm and the endoderm. There are no nematocysts. The endoderm here, as in all parts of the body, contains symbiotic zooxanthellæ, which are present in very large numbers. The circular muscle of the wall does not appear to be regularly developed through the whole length of the wall.
Tentacles.—Conical and gently tapering. Pore at tip. Colour bronze-green, like that of the oral disc. The tentacles are very sensitive, and completely and quickly retractile; they number 48, and are arranged in 4 cycles, the formula being 6 + 6 + 12 + 24 = 48. The ectoderm of the tentacles is thinner than that of the column. The epithelial layer contains numerous nuclei, but no cell-walls are distinguishable. There are numerous nematocysts. The nervous layer of the ectoderm appears as a fibrous network, with here and there what are apparently nerve-cells. The longitudinal muscles of the tentacles appear as pleatings of the mesoglœa. The mesoglœa is not so distinctly fibrous as that of the column; it is thin and vacuolated. The structure of the endoderm is almost completely obliterated by the great numbers of zooxanthellæ that are present. A few folds on the endodermal side of the mesoglœa indicate the circular muscles of the tentacles.
Sphincter Muscle.—In transverse sections of the upper part of the column the sphincter appears as a ring lying in the angle formed by the wall of the oral disc. In cross-section it is seen to be well developed, endodermal, and of the circumscribed type, not unlike the sphincter of Cradactis digitata figured by McMurrich.*
[Footnote] * “Scientific Results of Explorations by the United States Fish Commission Steamer ‘Albatross’” (Proc. U.S. Nat. Mus., vol. xvi, pl. xxxiii).
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Oral Disc.—The ectoderm resembles that of the tentacles. The nuclei are large, and there are fewer nematocysts. The radial or ectodermal muscles are strong, and are carried on deep pleatings of the mesoglœa. The mesoglœa is similar to that of other parts. The endodermal or circular muscles are weaker than the ectodermal. The “mouth” is borne on a prominent peristome surrounded by a broken circle of yellow, from which extend 6 groups, each consisting of 3 radiating yellow lines with a shorter yellow line between each 2 groups. These yellow radii correspond to the first 3 cycles of tentacles, the tentacles of the 4th cycle being set opposite to the interspaces.
Æsophagus.—The colour is greyish-white. There are 2 siphonoglyphs, with inconspicuous tubercles. The insertions of the mesenteries are shown by white markings. Each side of the œsophagus is thrown into 2 large lobes. Outgrowths of the mesoglœa, with corresponding foldings of the ectodermal lining of the œsophagus, give a much folded appearance, which in cross-sections somewhat resembles an exaggerated starfish.
Mesenteries.—There are 24 pairs of mesenteries, of which 12 pairs are perfect, 2 pairs being directives; they are arranged quite regularly—a pair of imperfect mesenteries in each exocœle of the perfect pairs. Strong retractor muscles are borne on the faces of the mesenteries. On the imperfect mesenteries they extend from near the body-wall to the inner end of the mesentery. The cells of the endoderm are spindle-shaped.
Gonads.—None present in any of the specimens sectioned.
Dimensions.—Oral disc 12 mm. wide in a good specimen. Height in full expansion rather more than 12 mm. The longest tentacles are about 8 mm.
Locality and Habits.—The only specimens I have seen were procured at Oriental Bay by Professor Kirk. The animal lives between tide-marks, almost completely buried in sand and mud. The presence of the zooxanthellæ probably enables it to adopt this habit. It lives well in captivity.