Botrylloides violaceus Oka, 1927

KOTT, PATRICIA, 2003, New syntheses and new species in the Australian Ascidiacea, Journal of Natural History 37 (13), pp. 1611-1653 : 1647-1648

Botrylloides violaceus Oka, 1927

(plate 1F)

Botrylloides violaceum Oka, 1927b: 608 ; Kott, 1985: 278 and synonymy.

Botryllus firmus: Monniot and Monniot, 1996: 238 .

Distribution. New records: Queensland (Moreton Bay, QM G308550). With the exception of another specimen from the Queensland coast (Sarina: Kott, 1985) and possible records from the Palau Is, Indonesia and Papua New Guinea (Monniot and Monniot, 1996), all the known records are from Japan where it is common from Hokkaido to Kyusu (Tokioka, 1953).

Description. Newly recorded colonies are flat plates to 3 cm diameter and about 5 mm thick. They have a layer of sand attached to the base of the colony but sand is not included in the flexible but tough test nor is there any on the upper surface. Zooids are vertical and occupy almost the whole thickness of the colony. They are in straight double rows, although these are not always parallel. There are more or less parallel wrinkles on the soft upper surface of the colony. Depressions sometimes (but not always) extend between rows of zooids, but often the rows of zooids run at angles to the ridges. Living colonies have large protuberant common cloacal apertures, but the branchial apertures are depressed into the test. Terminal ampullae, dark blue in life, are crowded between the rows of zooids. In preservative specimens are pale dusty pink, the zooids being pinkish and the gut a brighter pink which shows through the translucent test. Small buds, one each side of the posterior end of the zooids, also are bright pink.

Zooids are up to 3 or 4 mm long with a short, plain-rimmed branchial siphon and a variable atrial aperture, sometimes the body wall being produced out from the dorsal surface into a short siphon, but sometimes the opening is wide, exposing a large part of the middle of the branchial sac and it has a rounded anterior and posterior lip. Small clumps of spherical (blood?) cells are at the ventral end of each row of stigmata (each side of the endostyle). Stigmata are in 13–15 rows and are arranged according to the following formula: DL 5.2.3.3E. The proximal part of the gut is behind the branchial sac and a short narrow loop is horizontal or oblique. The rectum extends anteriorly to the atrial aperture. The barrrel-shaped stomach has 10 parallel longitudinal folds. An L-shaped caecum is in the gut loop. There are no gonads in these specimens.

Remarks. The present colonies have 13–15 rows of stigmata and Japanese specimens have 9–14. No other significant differences can be found between the known Australian specimens and the Japanese ones. The species is unusual in its plate-like colonies. The zooid systems resemble those of other colonies of Botrylloides in their long double-row systems but they are distinguished by the gastric caecum which is longer than in B. leachii and related species, and shorter than in B. anceps . The stomach and gastric caecum do resemble Botryllus schlosseri and B. stewartensis but the large atrial apertures and the long double rows of zooids distinguish the present species from these Botryllus spp. The lack of sand around the surface, the flat plates (rather than tall, vertical long colony lobes) and the long (rather than circular) systems further distinguish it from Botryllus stewartensis .

Kott (1985) assigned to this species other Australian tropical specimens which, like the present colonies, are morphologically identical to specimens included in Botrylloides violaceum Oka, 1927b (compare, especially the colonies, zooids, gut loop in Tokioka, 1953: plate XLIV, and Kott, 1985: figure 136). As in the newly recorded material, Kott (1985) did not find gonads in colonies she assigned to B. violaceus . These specimens also closely resemble Botryllus firmus Monniot and Monniot, 1996 , which was distinguished from Kott’s specimens largely on the course of the rectum—a character affected by the contraction and general condition of the zooid. Botryllus firmus has the same short stomach folds on the left side of the stomach as Tokioka (1953: plate XLV) figured for B. violaceus , and its gonads and atrial aperture show it to be a species of Botrylloides . Monniot and Monniot (1996) found, in B. firmus , a small testis in adult zooids and larger ones in first-generation buds which had second-generation buds containing oocytes. They conclude that this separates their species from others previously considered congeneric with Botrylloides violaceus Oka, 1927b (see Saito and Watanabe, 1985; Mukai et al., 1987 for maturation of five Botrylloides spp. ). The details of maturation recorded for B. firmus that would establish it as distinct from B. violaceus are not recorded.

Monniot, C. (1988) proposed that the use of the name Botryllus violaceus (Quoy and Gaimard, 1834) for a synonym of Botrylloides leachii made it a secondary homonym and unavailable in the combination Botrylloides violaceus Oka, 1927b . The combination Botrylloides violaceus was not used by any author until Oka (1927b) used it, and despite the fact that Monniot (1988) believes Botryllus to be the senior synonym of Botrylloides , Botryllus violaceus (Quoy and Gaimard, 1834) and Botrylloides violaceus Oka, 1927b were never in the same genus level taxon. The name Botrylloides violaceus for the present taxon is a valid name.