The Atoll of Funafuti, Ellice group : its zoology, botany, ethnology and general structure based on collections made by Charles Hedley of the Australian Museum, Sydney, N.S.W.
Sub-Class Zoantharia. — By J. P. Hill, B.Sc, F.L.S., and T. Whitelegge. — Family Zoanthidæ
By J. P. Hill, B.Sc, F.L.S., and T. Whitelegge.
Zoanthus Funafutiensis, sp. nov.
(Plate xxiv., figs. 2, 3).
Form.—Body-wall smooth, translucent, surface transversely wrinkled when contracted. Cænenchyme thin, encrusting, con-tinuous or becoming stoloniferous at the margin. Column short, often broader than high. Capitulum slightly expanded, with from 45 to 50 ridges, confined to the upper swollen surface. Oral cone a little prominent, aperture longer than broad. Tentacles 24 to 28, similar, arranged in two cycles.
Colour.—The specimens were preserved in formol, and when received were of a bright grass green. The colour has now faded entirely, and the colony is greyish with slight tinge of olive.
Dimensions of colony 8·5 by 4·7 cm.; height of an average-sized polyp 5 mm., diameter of the capitulum 5 mm., of the column 3 mm.
Body-wall (Plate xxv., fig. 1).—The body-wall is bounded ex-ternally by a cuticle to which stray diatoms and sponge spicules are found adherent. Between the cuticle and the ectoderm is a thin peripheral layer of mesoglæa, consisting of fine anastomosing strands, and having a thickness of ·003 mm. The ectoderm is a thin continuous layer in which cell outlines are not recognisable. It is crossed here and there by fine strands from the mesogloæ, which unite to form the peripheral layer as described by Haddon and Shackleton in Z. coppingeri.*
* Reports on the Zoological Collections made in Torres Straits: Actiniae, i. Zoantheæ—Sci. Trans. R. Dublin Soc. (2), iv,3 xiii., p. 677.
In the ectoderm there are present narrow oval nematocysts, 0·14 mm. long, but zooxanthellae are absent. Slightly branched canals arising from the ectoderm are present in the mesogloæ, but are not at all numerous, though somewhat more abundant in the lower part of the column. In the rarity of ectodermal canals the species under consideration agrees with Z. jukesii, H. & S., and as in that species lacunæ are fairly numerous. Small cell-groups and isolated rounded or spindle-shaped cells, produced into radially running processes, also occur in the mesogloæ. Nemato-cysts are present in the ectodermal canals in small numbers. In the lacunæ there occur very definite, small, rounded or oval bodies, often in considerable numbers. In general appearance these re-semble nematocysts, but are apparently quite homogeneous in-ternally and show no trace of threads.
The entoderm is thin, and contains nematocysts and numerous zooxanthellæ. The entodermal circular musculature is weakly developed, and supported by minute mesogloæl plaitings.
Capitulum.—The ectoderm here is ridged and thicker than that of the column-wall. It contains nematocysts.
Sphincter muscle.—The double mesogloæl sphincter muscle is well developed. Its upper portion is about three times the length of the lower. The latter consists of a single row of cavities, rounded in shape and larger than those of the upper portion which are small and compressed and not arranged in a single row. In both, the muscle fibres are supported on plaitings of the mesoglosæ.
Tentacles.—The ectoderm is thick and is crowded with enormous numbers of small sausage-shaped nematocysts, ·01 mm. in length. zooxanthellæ are absent. The ectodermal musculature, longitu-dinal in direction, is moderately strong and supported on small plaitings. The mesogloæ is thin, and contains only small scattered cells. The entoderm is a very thick layer. It contains numerous nematocysts similar to those of the ectoderm, and zooxanthellae are also numerous. The circular entodermal musculature is very weak.
Disc.—The ectoderm of the disc is ridged. It is in general similar to the ectoderm of the tentacles, but nematocysts are here not so numerous. The mesogloæ contains isolated cells and cell-groups. In the entoderm numerous zooxanthellae are present. The musculature of the disc is weak.
(Esophagus (Plate xxv., fig. 2).—The ectoderm is thrown into distinct longitudinal folds. The groove is wide and well marked. The ectoderm contains nematocysts, and here and there in the basal parts of the cells there occur groups of refractive yellow (pigment ?) granules. The mesogloæ forms a uniformly thin layer. The entoderm is also thin, and contains zooxanthellæ in no great page 387numbers. The ectodermal musculature, longitudinal in direction, and the entodermal, circular in direction, are both weakly developed.
Mesenteries (Plate xxv., fig. 2).—The mesenteries are slender, and have the normal brachycnemic arrangement. The reflected ectoderm of the æsophagus forms ridges (8-11 in number) along the two faces of each perfect mesentery, and is limited to the inner half of the radial extent of each mesentery. Below, the peripheral folds of the reflected ectoderm are continued on as the mesenterial filaments. These are at first V-shaped in section, but lower down the free limbs of the V soon disappear, and the ectoderm of the filament assumes a rounded bulbous form. At the same time the entoderm becomes thickened immediately below the filament, giving rise to a second bulb-like swelling. The ecto-derm of the filament contains numbers of deeply-staining gland-cells, and in its deeper part occur numerous small granules which stain slightly with eosin. Rod-shaped nematocysts also occur in the ectoderm, as well as in the thickened entoderm. The mesen-terial filaments continue to near the base of the column, and are considerably folded. The mesogloæ of the mesenteries is a thin layer, which, however, becomes somewhat thickened just before joining the body-wall. In this outer thickened part is situated the single basal canal of the mesentery. In the lower part of the column, the mesogloæ of the mesenteries is somewhat thicker and the basal canals are larger. The entoderm of the mesenteries is a thin layer containing zooxanthellæ, which are usually much more numerous on one face of the mesentery than on the other. Nematocysts are sparingly present in the entoderm. The parieto-basilar muscles are supported on mesogloæl plaitings, and are well developed. The longitudinal musculature is fairly well developed, and supported on small plaitings.
Gonads,—Gonads were not present in any of the specimens examined by us.
This species is closely related to Z. jukesii, H. & S., but is to be easily distinguished by, among other points:—(1) its smaller size, (2) its green coloration, (3) the absence of nematocysts from the entoderm of the tentacles.
Gemmaria willeyi, sp. nov.
(Plate xxiv., figs. 1 and 4).
Form. —Body-wall opaque, encrusted with foreign matter and minutely granular. Surface even when extended, transversely wrinkled when contracted. Cænenchyme incrusting, forming broad expansions or band-like stolons. Column often slightly swollen in the middle. The capitular region greatly expanded, with about forty very short radial ridges. Disc large, radiately ridged. Oral cone prominent, aperture oblong. Tentacles short, subequal, eighty in number, arranged in two cycles.page 388
Colour.—As per coloured sketch, drawn by Mr. C. Hedley on the spot. Column pale green, capitulum pinkish, disc pale violet, tentacles brownish-orange; in formol, yellowish-grey.
Dimensions.—Length of largest colony, 7 cm.; breadth, 5 cm. Length of largest polyp, 1·7 cm.; diameter at base, 5 mm.; in the middle, 7 mm.; at the capitulum, 11 mm.; diameter of disc about 8 mm.; oral aperture, 3 mm. by 1·5 mm. Length of tentacles about 1·8 mm.; contracted examples are usually somewhat flat-tened at the summit—varying from 6 to 10 mm. in diameter—and frequently broader at the summit than long.
Body-wall (Plate xxvi., fig. 1).—The ectoderm is thick, measur-ing in breadth ·07 mm., and forms a definitely continuous layer. It is provided externally with a thin cuticle, to which occasional diatoms adhere. A peripheral layer of mesogloæ is absent. Numerous incrustations consisting of grains of calcareous sand, foraminiferal shells etc., are present in the ectoderm and peri-pheral portion of the mesogloæ, forming a layer about ·15 mm. thick. Owing to the presence of these incrustations, the ectoderm appears in decalcified sections considerably broken up, and is here and there separated by a space, extending over a considerable area, from the underlying mesogloæ. The ectoderm contains zooxanthellæ in considerable numbers and also numbers of large nematocysts. One of the largest of the latter observed measured 1·35 mm. in length by ·06 mm. in breadth, but their average size is considerably less than this.
As is characteristic of the genus, ectodermal canals are absent from the mesogloæ. Large rounded or oval lacunæ are, however, abundant in the outer two-thirds of the layer. The lacunæ con-tain large nematocysts (usually one in each), similar to those of the ectoderm and also contain numbers of zooxanthellæ. Besides lacunæ small cell-islets and isolated cells produced into very dis-tinct radial processes are present in the mesogloæ. Except in its most peripheral portion, below the ectoderm, the mesogloæ is almost completely devoid of incrustations. Occasional siliceous spicules however do occur.
The entoderm of the body-wall is thickened between the mesenteries and contains zooxanthellæ but they are here not so numerous as in the ectoderm. The circular entodermal muscula-ture is well developed.
Capitulum.—The outer surface of the capitulum is ridged, the ridges alternating with the tentacles of the outer cycle. The ectoderm is thicker than that of the column and is not so densely crowded with incrustations. These are here more abundant in the outer part of the mesoglcea.page 389
Sphincter Muscle.—The single mesogloæl sphincter muscle is well developed (Plate xxvii., fig. 1, m.s.). The muscle cavities are large and arranged in an irregular alternating fashion.
Tentacles.—The ectoderm of the tentacles is crowded with small slightly curved nematocysts (·010 mm. long), among which occur occasional large ones. ZooxanthellÆ are also very numerous. The longitudinal ectodermal musculature is strongly developed and supported on close-set plaitings of the mesogloæ. The mesogloæ is of moderate thickness and contains only small isolated cells. The entoderm is thin. It contains numerous zooxanthellæ but no nematocysts. The circular entodermal musculature is moderately strong.
Disc (Plate xxvi., fig. 2).—The disc is traversed by ridges which pass one from the base of each tentacle of the inner and outer rows to the margin of the mouth. In the ridges both ectoderm and mesogloæ are somewhat thickened. The ectoderm especially on the ridges contains nematocysts similar to those in the tentacles and also zooxanthellæ. In the deeper portion of the ectoderm there occur numbers of small bright refractive (pigment?) granules. The ectoderm is devoid of incrustations.
The mesogloæ of the disc is thick, and especially noteworthy from the presence in it of numerous large ectodermal muscle cells (fig. 6, ect. m.) These project into the mesogloæ so obliquely that in sections they mostly appear as isolated masses which occupy the upper two-thirds of the mesogloæ, and extend from the margin of the mouth across the horizontal part of the disc and for a short distance up in its vertical part (fig. 7).
McMurrich, and Haddon and Shackleton, also describe enclosures in the disc mesogloæ of the species of Gemmaria examined by them. In G. isolata, McMurrich *describes the mesogloæ of the disc as being "densely loaded with enclosed cavities containing cells probably ectodermal and muscular," but in his later descrip-tion of G. rusei, D. & M., he says, † "the enclosures in the mesogloæ of the disc which I thought might possibly be muscle cells in isolata, are seen in Rusei to be comparable to the lacunæ of the column wall." Again Haddon and Shackleton in their des-cription of G. macmurrichi (page 689), remark that "cell enclosures (similar to those described and figured by McMurrich) are found in the disc of G. macmurrichi," and they also mention the occur-rence of such in G. mutuki. May it not be that in all these cases we have to do as in the species under description with ectodermal muscle cells, and may not the existence of such in the mesogloæ of the disc be a character diagnostic of the genus?
* The Actiniaria of the Bahama Islands.—-Jour, of Morphology, iii. p. 64.
† A contribution to the Actinology of the Bermudas.—Proc. Acad. Nat. Sci. Phil., 1889, p. 125.
The entoderm of the disc is thin and contains zooxanthellæ. The entodermal musculature is weak.
CEsophagus.—The groove (Plate xxvii., fig. 2gr.)is well marked and has in one specimen examined by us, the same truncated form described by McMurrich in G. isolata, and Haddon & Shackleton in G. mutuki. The ectoderm contains large and small nematocysts and a few zooxanthellæ are also present. In the basal part of the ectoderm colourless refractive granules as well as groups of yellowish-brown granules are present. The mesogloæ is considerably thickened below the groove.
Mesenteries.—The mesenteries are typically brachycnemic in arrangement (fig. 8), but in one specimen examined the sulcar mesentery of the second pair on one side was perfect, thus realis-ing the macrocnemic condition. The mesogloæ of the mesenteries is on the whole thin but is somewhat thicker in the basal part of the column. Peripherally also the mesogloæ in each perfect mesentery is thickened where it encloses the basal canal and again becomes constricted before joining the body wall. The imperfect mesenteries are short and bulbous and project little into the cælenteron (fig. 8).
Each mesentery encloses a main basal canal appearing in section narrow and elongated in the perfect and rounded in the imperfect mesenteries. In the mesogloæ internally to the basal canals in the perfect mesenteries there occur small lacunæ. In the basal canals there are present large nematocysts similar to those in the lacunas of the body-wall, and zooxanthellse also occur in the canals and lacunæ, but in no great numbers. The basal canals run up into the region of the disc where they divide into several smaller canals.
The entoderm is a thin layer in which zooxanthellæ are fairly abundant, especially in the æsophageal region.
Occasional nematocysts are also present. The parieto-basilar muscles are supported on plaitings of the mesogloæ and are well developed. The longitudinal musculature is weak.
The reflected ectoderm on the two sides of each perfect mesentery give rise to numerous (up to 20) close set ridges of which the inner and outer project freely. Below, the peripheral free portions pass into the mesenterial filaments in the usual fashion. The filaments have at first in section the shape of an arrow-head, but soon the free margins disappear and the central part remains as a bulbous thickening below which the entoderm is also enlarged. Here, just as in Z.funafutiensis, the inner margin of the mesentery has the shape in section of a double bulb. In the ectoderm of the filament there are present occasional zooxanthellse and large nematocysts, while gland cells are very numerous. A few large page 391nematocysts also occur in the thickened entoderm, and zooxanthellæ are here more numerous than in the ectoderm of the filament. The filaments are convoluted below and terminate some distance from the base of the column.
Gonads.—In one of the specimens examined by us ovaries were found as small whitish swellings disposed in irregular longitudinal rows along especially the lower portions of the mesenteries, in the region of the mesenteric filaments.
In G. mutuki, Haddon and Shackleton record finding ripe sperm cells in the cælenteron of one individual.
We have much pleasure in associating this well marked species with the name of our friend Dr. A. Willey, in appreciation of his untiring labours in the South Seas.
Palythoa howesii, Haddon and Shackleton.
Palythoa howesii, Haddon and Shackleton, Sci. Trans. R. Dublin Soc. (2), iv., 1891, p. 693, pl. lxi., fig. 13; pl. lxiii., fig. 8.
A single example is here referred to this species. Several specimens from Thursday Island are in the Museum collection, with which the Funafuti example has been compared and found to agree in all the external characters.
The specimen consists of an oblong colony 9 cm. long, 3 cm. wide and 1·4 cm. high, the basal cænenchyme forms a projecting margin all round the colony, from 2 to 5 mm. wide, and from 1 to 3 mm. in thickness. The polyps are about 7 mm. in diameter. The capitular ridges number about 28 or 30.
Palythoa kochii, Haddon and Shackleton.
Haddon and Shackleton, Sci. Trans. R. Dublin Soc. (2), iv., 1891, p. 694, pl. lxi., fig. 12; pl. lxiii., fig. 9.
A small specimen agreeing in its general characters with examples of this form from Thursday Island. It is a thin incrusting colony 6 cm. long, 3·5 cm. wide and having a pretty uniform thickness of 7 mm. The capitular ridges are very variable in number from 15 to 20. The polyps are however much contracted and the ridges more or less indistinct.
Palythoa cœsi A, Dana.
Dana, U.S. Explor. Exped., Zooph., p. 40, pl. xxx., fig. 3, 3a to 3h; Haddon and Shackleton, Sci. Trans. R. Dublin Soc. (11), iv. 1891, p. 695, pl. lxi., fig. 14.
Two specimens both more or less biconvex in shape. The larger example is 3·6 cm. in diameter and 3 cm. in height. Polyps about 15 mm. high and 9 mm. in diameter. The upper surface and tentacles are of a bright reddish maroon colour. The specimens are in formol.page 392