Synoicum georgianum Sluiter, 1932

Primo, Carmen & Vázquez, Elsa, 2007, Ascidians collected during the Spanish Antarctic expedition CIEMAR 99 / 00 in the Bransfield and Gerlache Straits, Journal of Natural History 41 (29 - 32), pp. 1775-1810 : 1788-1791

Synoicum georgianum Sluiter, 1932

( Figure 10 )

Synoicum georgianum Sluiter, 1932 ; Millar 1960, 1968; Monniot F 1970; Vasseur 1974; Monniot and Gaill 1978; Monniot and Monniot 1983; Sanamyan and Sanamyan 2002; Tatián et al. 2005. Aplidiopsis georgianum: Kott 1969, 1971 .

Distribution

New record: Bransfield Strait (Station B7: four specimens). Previously recorded: Antarctic Peninsula, Wilkes Land ( Monniot and Monniot 1983); Scotia Arc Islands ( Monniot and Monniot 1983; Tatián et al. 2005); Kerguelen Island ( Monniot and Gaill 1978); Magellan Strait ( Monniot and Monniot 1983). From 20 to 552 m depth.

Description

Small colonies (up to 31 mm in our specimens) with basal processes ( Figure 10a ) to attach to substrata. Few systems of zooids (usually one) per colony; small zooids (about 5 mm) with few rows of stigmata (15 in our specimens) and gonads a little separated from the gut loop ( Figure 10b ).

Remarks

Frequently confused with Synoicum adareanum ( Herdman, 1902) . After re-examining the holotype (no. 489 T) we conclude that, despite the great variety of shapes, our specimens belong to this species because of the few zooid systems, the root-like processes of the colony, the small size of zooids, few rows of stigmata and the location of the gonads .

Synoicum ostentor Monniot and Monniot, 1983

( Figure 11 )

Synoicum ostentor Monniot and Monniot, 1983 ; Ramos-Esplá et al. 2005.

Distribution

New record: Bransfield Strait (Station B6: four specimens). Previously recorded: Wilkes Land ( Monniot and Monniot 1983); South Shetland Islands ( Ramos-Esplá et al. 2005); Balleny and South Orkney Islands ( Monniot and Monniot 1983). From 0 to 350 m depth.

Description

Stalked colonies (from 19 to 112 mm height) with a slight constriction between head and stalk ( Figure 11a ). Circular systems. About 20 rows of branchial stigmata with 20 stigmata per half-row ( Figure 11b ). Zooids are immature.

Remarks

Our specimens coincide with the holotype described by Monniot and Monniot. (1983) except for few stigmata per half row (20 in our specimens versus 35 in the holotype). Synoicum ostentor is close to Synoicum adareanum , but S. ostentor has a constriction between head and stalk and a more marked difference in the texture of both parts. Zooids are similar size, but differ in a greater number of rows of stigmata, and stigmata per row, and greater distance between abdomen and ovary in S. ostentor . This is the second record of this species since its description by Monniot and Monniot (1983).

Synoicum polygyna Monniot and Monniot, 1980

( Figure 12 )

Synoicum polygyna Monniot and Monniot, 1980 ; Monniot and Monniot 1983, 1994.

Distribution

New record: Bransfield Strait (Station B7: two specimens). Previously recorded: Weddell and Ross seas ( Monniot and Monniot 1980, 1994). From 20 to 252 m depth.

Description

Cylindrical colonies up to 30 mm with irregular basal processes ( Figure 12a ). Strong tunic with embedded sand. One system per colony with the common cloacal opening in the upper part. Zooids up to 15 mm. Long branchial siphon with six lobes; tubular atrial siphon with three lobes from the dorsal border and three minute lobes more from the ventral border ( Figure 12b ). Branchial sac with 14 rows of stigmata. Initial constriction of the oesophagus (hardly visible because of the great contraction of the animals). Smooth, large, rounded stomach. The gut loop does not show torsion. All the specimens are immature.

Remarks

The description agrees with the holotype re-examined at MNHN (registration number A1 711-716 and A1 SYN-29) (the atrial siphon, and the constriction of the oesophagus being characteristic) except for the fact that in this case the whole colony is incrusted with sand and is not naked on the upper part. The zooids are shorter, but this may be due to the absence of gonads.

Synoicum polygyna is similar to Synoicum ramulosum Kott, 1969 . The only differences are smaller colonies and zooids, fewer rows of stigmata and absence of constriction of the oesophagus in S. ramulosum . It could be possible that Kott’s specimens were juveniles of S. polygyna .

Figures

Figure 10. Synoicum georgianum. (a) Colony; (b) zooid.

Figure 11. Synoicum ostentor. (a) Colonies; (b) thorax and abdomen.

Figure 12. Synoicum polygyna. (a) Colonies; (b) thorax and abdomen.