Botrylloides anceps ( Herdman, 1891 )

Brunetti, Riccardo, 2009, Botryllid species (Tunicata, Ascidiacea) from the Mediterranean coast of Israel, with some considerations on the systematics of Botryllinae *, Zootaxa 2289, pp. 18-32 : 21-22

Botrylloides anceps ( Herdman, 1891)

Sarcobotryloides anceps Herdman, 1891: 609 ; 1899: 103, pl. bot. II, figs 9–13, Port Jackson, Australia.

Botryllus anceps: Michaelsen, 1928 (in Hartmeyer & Michaelsen): 334, fig. 21, New Zealand.

Botryllus gracilis Michaelsen, 1927: 203 ; 1928 (in Hartmeyer & Michaelsen): 338, figs 22, 23, Skart Bay, Western Australia;? Hastings, 1931: 77, Australia; Millar, 1966: 367, Port Phillip, Australia. Not Tokioka, 1961: 112, fig. 6, New Caledonia; Monniot, 1988: 164, fig. 1, New Caledonia.

Botryllus humilis Monniot C., 1988: 173 , figs. 4, A–C, New Caledonia.

Material examined: several colonies from the Bay of Àkko (May 1991,? 2004) and Mikhmoret (July, August, November 2007).

Description. The colony is about 1.5 mm thick, grey in preservative. Living animals are grey, cream and violet. The test surface is sandy, with very fine particles. All structures are colourless, and the test is transparent but made opaque by high numbers of two cell types, the larger one 1 μm in diameter. The zooids, up to 1.5 mm tall, lack atrial siphons and are arranged in “ leachii - type ” systems. The oral siphons are not lobed but, observed at strong magnification, their edges appear to be very minutely indented (Plate 2, e1, e2). Two small pigmented spots are often present on the dorsal lip of the atrial opening (Plate 2, d). They are clearly visible in young colonies; in older ones, they are sometimes visible in specimens prepared for microscopic observation. There are two large lateral tentacles, moving towards the endostyle (“ten to two” position). There is a vascular lacuna at their base, filled with pigmented blood cells which, in some colonies, may be very large (Plate 2, c). These cell masses are often visible from the surface of the colony as two dark spots on the sides of the oral opening (Plate 2, a). The dorsal tubercle has a small, oval, longitudinal opening; it is connected by means of a long duct to the neural gland, which is, unusually, located separated and posteriorly to the cerebral ganglion (Plate 2, b, c). The branchial sac is conical, with 9 rows of stigmata, the 2nd row being dorsally incomplete and the 9th formed only of a few irregular stigmata (Plate 2, b). The branchial formula is usually 4,3,3,4 DL 4,3,3,5 at the middle of the pharynx. A mass of pigmented blood cells is present on each side of the endostyle at the level of the stigmata rows (Plate 2, b). The surface of the dorsal vessel exposed towards the lumen of the branchial sac is concave, forming a groove. The posterior edges of the pre-pharyngeal groove continue, as two wing-shaped expansions, along the edges of the dorsal groove (Plate 2, c). A true dorsal lamina rises only slightly before the oesophageal opening, and is double (Plate 2, c). The stomach is more or less globular, with 10 folds, excluding the typhlosolis. Rarely, there are only 9, and the 9th is posteriorly divided into two. The folds, extending the whole length of the stomach, are slightly spiral and closed at both ends, which are equal and not swollen (Plate 2, f, g1–g4). The typhlosolis extends over the pyloric end of the stomach in the first tract of the intestinal loop. A pyloric caecum rises from its posterior stomachal tract, as long as or longer than the length of the stomach; it initially rises perpendicularly to the longitudinal axis of the stomach and then, half-way along, bends at right angle towards the pyloric end of the stomach. Its distal tract, only slightly swollen, is connected to the body wall (Plate 2, g1–g4). The duct of the pyloric gland is connected to the pyloric caecum, where it bends at right angles (Plate 2, f, g1, g2). In some very young colonies (formed of only 10–20 zooids), I observed slightly different stomach morphology: the folds were only 8 in number, had a longitudinal median groove, and were slightly spaced (Plate 2, g3, g4). These colonies had no gonads yet, and their branchia had one or two fewer rows of stigmata.

The anterior edge of the intestinal loop reaches the penultimate row of the stigmata. The anus opens at the same level or immediately anteriorly. Its aperture is smooth-edged; however, when the terminal tract of the rectum is contracted, the edge overflows and appears bilobed (Plate 2, f). In the buds, several oocytes per side are present, dorsally to the testis. However, in adult (i.e., filtering) zooids, there is only one egg per side, located anteriorly to the testis follicles, which partially envelop it like a cup. The egg develops in the body wall, and there is no incubatory pouch.

Remarks. Sarcobotrylloides anceps from Port Jackson ( Australia) was described by Herdman (1899) as a species with zooids arranged in Systems numerous and close, forming branching lines. (p. 103), that is, as a “ leachii type ”. The zooids are 1.5 to 2 mm long, with 11 rows of stigmata. The stomach is globular, with a long caecum. The anus has an everted rim. All other characteristics described may be attributed to any botryllinae species. Sarcobotrylloides anceps was recognised as valid by Michaelsen (in Hartmeyer & Michaelsen, 1928), who turned his attention to the morphology of the stomach. The great zoologist described the pyloric caecum at right angles and observed the space among the folds. In the same work, he also described Botryllus gracilis as a species different only in that the stomach folds have a longitudinal groove. Neither of the species had gonads. I believe that Michaelsen’s two samples were juvenile stages of the same species: Botrylloides anceps ; B. gracilis being the younger and the Israeli colonies the mature stage. The following data may confirm this hypothesis.

The characteristics of Botryllus humilis Monniot, 1988 , from New Caledonia fit B. anceps and is here considered as a junior synonym. Botryllus gracilis: Hastings, 1931 , is insufficiently described. Botryllus gracilis: Tokioka, 1961 , fig. 6, from New Caledonia, has a pyloric caecum described as very large, strongly curved in a semicircular form and ending in a slightly swollen tip. (p. 113), like that of Monniot, 1988 (p. 164), of which the author gives only the following information: L’estomac est globuleux, en forme de ballon, avec des crêtes nettes. Il y a un très grand caecum en crosse, élargi son extrémit.(p. 165). The pyloric caecum is en crosse, that is, shaped like a shepherd’s staff. It is possible that neither species is the present one.