Isoparactis ferax (Sea Anemones of New Zealand)

Isoparactis ferax

Description ²

Attached beneath rocks, and curves up in a "J" shape through the sediment to bring its mouth and tentacles above the surface.

Edited version of Transactions and Proceedings of the Royal Society of New Zealand 1868-1961, Volume 41, 1908, p387-8
Art. XXXVI.—A Review of the New Zealand Actiniaria known to Science, together with a Description of Twelve New Species.
By F. G. A. Stuckey, M.A., Wellington.

Genus Paractis(Andres).

“Paractidœ with smooth body-wall, without papillæ or marginal spherules; tentacles slender, and not exceptionally numerous; nearly equal in length and strength; margin not lobed; sphincter widening somewhat abruptly in its upper part, and occupying, near the margin, nearly the entire thickness of the mesoglœa.”

Paractis ferax (sp. nov.).

Pedal-disc.—Adherent to the under-sides of stones, or to rocks, in dark places. The chief histological feature is the thick mesoglœa, which is indeed a noticeable feature of the whole animal. The fibres are wavy, and there are many lacunæ. The ectoderm is of the usual type, about half as thick as the mesoglœa. The endoderm is thin.

Column.—It is generally cylindrical in shape, but is occasionally constricted at various parts, giving the animal a vase-shaped contour. The column bears, especially in contraction, fine transverse wrinkles. Its height can be varied very considerably, but is generally equal to two or three times the diameter. The colour is milky white. In contraction the animal is drawn into a hard rounded ball of the size of a small marble. The ectoderm and endoderm are of the normal type. The mesoglœa is thick, about equal to the ectoderm, but at intervals it becomes thin, as shown in fig. 9. This feature seems to be characteristic. In other places, numerous enough for the structure to be considered characteristic, the mesoglœa forks, sending out a process which is lined on both sides by ectoderm, and which lies close to the body-wall.

Tentacles.—These are conical in form, tapering to a fine point, and reducible to thin filaments. In colour they are white, with brown markings. Each has a brown tip. They are arranged very evenly in four cycles, the inner two nearly equal. Each of these two contains 6 tentacles; the third contains 12 slightly shorter; the fourth contains 24, shorter still. The ectodermal muscles are strong, and are borne on long processes of the mesoglœa. The mesoglœa is very fibrous, and contains a large number of nuclei. There are numerous nematocysts.

Oral Disc.—The disc is white, with a slight brownish tinge. Some specimens have radiating brownish lines. There is a pair of opaque-white lines radiating from the siphonoglyphs to the edge of the disc. The mouth is somewhat depressed, and the siphonoglyphs are not prominent. The stomodæum is not readily everted. The histological characters of the disc closely resemble those of the tentacles.

Sphincter Muscle.—This is mesoglœal in character, consisting of a thickening of the mesoglœa in the upper part of the column, the thickened portion containing numerous muscle-spaces. The whole mesoglœa of the wall is muscular, producing, no doubt, the strong contraction which is so characteristic of the animal.

Mesenteries.—There are 32 to 36 pairs, 2 pairs being directives. The musculature is very strong, the muscle-banners appearing as great rounded masses, but slightly attached to the mesentery.

Gonads.—The mesenteries are all fertile, except the directives. All the animals sectioned happened to be females, and all showed remarkable fertility. Ova appeared at nearly all stages. At first they occupy a position imbedded in the mesoglœa, but as they advance in maturity they form great masses, almost filling the intermesenterial spaces. Finally they may become detached from the mesenteries and form globular masses, showing in cross - sections as rounded discs or rings. No embryos were seen.

Habits.—All my specimens were found in dark places, never more than four in one place, usually single specimens. The species seems rather uncommon.

Dimensions.— 2—18 mm. in diameter, 25—45 mm. in height.

Distribution.— Island Bay, Ohiro Bay.

References ²

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