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Genus Botryllus Gaertner and Pallas.
Arnbäck-Christie-Linde and Michaelsen in their recent papers recognise two genera—Botryllus, forms with ovaries anterior or dorsal to the testis and no incubatory pouch, and Botrylloides (synonymous with Metrocarpa Arnbäck), forms with a single ovary with one large egg on each side of the body situated posterior to the testis and with an incubatory pouch present. In both genera the anterior margin of the atrial orifice may be produced into a long languet.
Botryllus leachi Savigny. (Text Fig. 12; Plate 2, Fig. 3; Plate 4; Fig. 4.)
For Synonymy and Literature see: 1922, Botryllus leachi, Michaelsen, Vidensk. Medd. naturh. Foren., bd. 73, p. 479.
This species forms soft, flat, irregularly-shaped masses on the sides and under-surfaces of rocks between tide marks in all three localities. Purple is the dominant pigment, but, as it varies in depth and as varying amounts of yellow or white pigment are present around the branchial apertures, a wide colour range occurs. The test is grey, semi-transparent, and the darker zooids and the terminal bulbs of vessels, especially numerous around the edge of the colony, show clearly through it. The zooids are arranged in extensive elongate or circular systems (Plate 2, Fig. 3) around the common cloacal apertures, which are inconspicuous and 1.5 to 3.0 mm. in diameter. Branchial apertures are 1.0 to 1.5 mm. in diameter and are without lobes. The largest colony measured 30 cm. in the longest diameter. The height above the substratum ranges from 2.0 to 5.0 mm., but does not vary greatly in the one colony.
Text Fig. 12.—Botryllus leachi. Left side of zooid. × 30.
Zooids measure up to 4.5 mm. in length and 2.0 mm. in width The mantle is thin and bears a few widely separated muscle fibres It closely surrounds the zooid except on the dorsal side. The atria [ unclear: ] aperture is a large, straight-edged slit, distant from the anterior end of the zooid by about one-third of the body length. The pharynx is narrow, elongate, occupies almost the entire length of the zooid, and bears three longitudinal vessels on each side. The wall of the pharynx is broken by fifteen or sixteen rows of nineteen or twenty stigmata, arranged between longitudinal vessels as follows: endostyle 5/4/4/6–7 dorsal lamina. There are no marked differences in size of the transverse vessels. Branchial tentacles are sixteen in number and of three orders of size, regularly arranged. The dorsal lamina is a plain, straight membrane. The gut loop lies on the left side of the branchial sac, and is composed of a short, narrow oesophagus, which takes a semi-circular course; a wide-lobed stomach with nine folds arranged on a slight spiral and with a short, wide, upwardly-directed gastric caecum; and a wide, smooth-walled intestine covered for a certain
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portion of its length by an external intestinal gland. The edge of the anal aperture is without lobes.
Sex organs were not seen in any colonies collected before December, 1944. Small lobed testes were present in the zooids of a few colonies collected during that month, but ovaries could not be detected in any. In January and February, 1945, testes were present in the majority of the colonies examined. Ovaries were not discernible until the end of January, and then only in a few colonies. One or occasionally two eggs are present and they are situated level with or just in front of the much-lobed testis. The gonads on the left side lie higher up the pharynx than those on the right side. Small orange tadpoles (Plate 4, Fig. 4) were present in the cloacal cavities between the beginning of March, 1945, and the end of April, 1945. The largest measured 1.4 mm. in length and 0.27 mm. in width in the head region.
Distribution: In New Zealand—Hauraki Gulf, Tauranga, Stewart Island (Mich.), French Pass (Sluit.), Otago Harbour. Elsewhere—Auckland Island (Bovien), North-West Ireland, Northern France, Skaggerak and Kattegat (Mich.).
Remarks: As far as can be ascertained, the specimens described above are identical with those considered by Michaelsen to belong to the species Botryllus leachi.
Botryllus schlosseri (Pallas). (Text Fig. 13; Plate 2, Fig. 2; Plate 4, Fig. 5.)
For Synonymy and Literature see: 1922, Botryllus schlosseri, Michaelsen, Vidensk. Medd. naturh. Foren., bd. 73, p. 481.
This species is rare and has been found on the under-surfaces of rocks between tide marks at Goat Island and on the branches of Cystophora torulosa (R. Br.) at the Portobello Point. To date no specimens have been found at Quarantine Island. The colonies form firm, flat, irregularly-shaped masses. The test is in all cases light yellow and transparent. The zooids are purple, green, or brilliant orange in colour and are arranged in small circular or elliptical systems (Plate 2. Fig. 2) around the common cloacal apertures, which are almost circular, 1.0 to 2.0 mm. in diameter, and each of which serves as an exit for ten to twenty zooids. The systems may lie close together or be separated by distances of up to 1.0 cm. Traces of scarlet and white pigment are sometimes present
Text Fig. 13.—Botryllus schlosseri. Left side of zooid. × 30.
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on the anterior ends of the zooids and on the edge of the common cloacal apertures. Branchial apertures are 0 8 to 1 0 mm. in diameter and without lobes. The largest colony measured 10 cm. in the longest diameter. The height of the colony above the substratum ranges from 1.0 to 4.0 mm., and does not vary greatly in the one colony.
Zooids measure up to 2.5 mm. in length and 2.0 mm. in width. The mantle is thin and bears a few widely separated muscle fibres. The mantle surrounds the zooid closely except on the dorsal side, and on this side it is produced above the atrial aperture into a long lappet-like process. The pharynx is wider than that of B. leachi and occupies almost the entire length of the zooid. There are three longitudinal vessels in the pharynx wall, which is broken by nine or ten rows of sixteen, nineteen or twenty stigmata arranged between the longitudinal vessels as follows: endostyle 5/3/3/5 dorsal lamina, or endo-style 5/4/4/6–7 dorsal lamina. There are no marked differences in size of the transverse vessels. Branchial tentacles are eight or sixteen in number and belong to two or three orders of size, regularly arranged. The dorsal lamina is a plain straight membrane. The gut loop lies on the left side of the branchial sac, and is composed of a short semi-circular oesophagus; a wide oval stomach with nine or ten folds arranged on a slight spiral and with a long tubular, much curved, gastric caecum; and a smooth-walled intestine, covered for a certain portion of its length by an external intestinal gland. The edge of the anal aperture is not lobed.
Sex organs were discernible only in the spring and summer months. A much-lobed testis and an ovary consisting of from one to three eggs are present on each side and are symmetrically arranged. The eggs form a slight arc anterior to the testis. The tadpoles (Plate 4, Fig. 5) are small, a light orange in colour, and were found in the cloacal cavities of specimens collected in March and April, 1945. The largest measured 0 8 mm. in length and 0.2 mm. in width in the head region.
Distribution: In New Zealand—North Island (exact locality not known) (Michaelsen), Otago Harbour. Elsewhere—East Coast of America and the whole of Europe (Michaelsen).
Remarks: As far as can be ascertained, the specimens described above are identical with those described by other systematists as B. schlosseri.