Botryllocarpa elongata Kott, 1990

Kott, Patricia, 2005, Novel Australian Polyzoinae (Styelidae, Tunicata), Journal of Natural History 39 (32), pp. 2997-3011 : 3008-3010

Botryllocarpa elongata Kott, 1990

( Figures 4 , 5D ) Botryllocarpa elongata Kott 1990, p 283 .

Distribution

New record: Tasmania (Tasman Peninsula, Waterfall Bay , on rock wall 12–14 m, SAM E3232 ). Previously recorded (see Kott 1990): Victoria (Phillip I.) .

Description

The newly recorded colony consists of elongate, transparent heads containing one to three transversely orientated zooids, each head attached to a basal stolon by a short, narrow thread-like stalk. Zooids are spherical, about 1 mm diameter, delicate and transparent. The apertures are minute and appear to be smooth-rimmed. They open directly to the exterior on short siphons, the branchial aperture from near the undersurface of the head and the atrial aperture uppermost. Circular muscles can be seen around the apertures but were not detected on the rest of the body. The branchial sac has three internal longitudinal vessels per side, seven rows of about 18 stigmata per row and three to four stigmata per mesh. The gut forms an almost horizontal loop across the posterior end of the left side of the body. The barrel-shaped stomach has eight longitudinal folds and a caecum that arises as a narrow tube, crosses the outside of the distal end of the stomach and expands into a rounded knob in the gut loop. A large egg is attached to the atrial wall on the left side of the body, anterior to the gut loop. A testis was not detected in these zooids.

Remarks

The newly recorded specimens have been assigned to this little known genus on the basis of its separately opening apertures, its flat branchial sac with only three internal longitudinal vessels, and only one single sex (female) gonad on the left side of the body. The absence of male gonads may be either because individuals are dioecious or, more likely, the gonads are ephemeral as they so often appear to be in this subfamily. In the type specimen ( Kott 1990), a single, lobed male follicle is on each side of each zooid and female gonads were not detected.

The only other known Botryllocarpa sp. is the type species, B. viridis ( Pizon, 1908) from Indonesia and the Pacific coast of Costa Rica (see Kott 1990), which is reported to have fewer testis lobes and more stomach folds than the present species and a separate male and a female gonad on each side of the body.

The related genus Chorizocarpa Michaelsen, 1904 (see Kott 1985) is known from three species, C. sydneyensis Herdman, 1891 from New South Wales to the tropical western Pacific, C. guttata Michaelsen, 1904 from New South Wales, and C. michaelseni ( Sluiter, 1909) from the Torres Strait. Like Botryllocarpa and Botryllinae , the genus also has three internal longitudinal branchial vessels and similar colonies. However, unlike the present genus, all three of the known species of Chorizocarpa are reported to have only one unisexual gonad on each side, the female on the right and the male on the left (anterior to the gut loop).

Kott (1990) appears to have overlooked the unusual origin of the stomach caecum from a suture line along the outer or postero-ventral edge of the stomach, which makes a rightangled bend across the distal end of the stomach (across its longitudinal axis) and terminates in a spherical bulb in the pole of the gut loop. The caecum is similar to that found in some species of the Botryllinae and in Chorizocarpa michaelseni Sluiter, 1909 (see Kott 1990). Although the present genus has similar gonads to some species of Botryllinae , it is distinguished by the absence of common cloacal systems.

Figures

Figure 4. Botryllocarpa elongata (SAM E3232). (A) Zooid; (B) gut loop. Scale bars: 0.1 mm.

Figure 5. In situ images. (A) Polyandrocarpa colemani (QM G308755) (photograph: Merrick Ekins); (B) Oculinaria australis (SAM E3267) (photograph: K. Gowlett Holmes); (C) Stolonica vermiculata (QM G308756) (photograph: Neville Coleman); (D) Botryllocarpa elongata (SAM E3232) (photograph: K. Gowlett Holmes).