Aplidium miripartum Monniot and Monniot, 1983

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 : 1783-1785

Aplidium miripartum Monniot and Monniot, 1983

( Figure 7 )

Aplidium miripartum Monniot and Monniot, 1983 .

Distribution

New record: Bransfield Strait (Station B 3: two specimens). Previously recorded: Antarctic Peninsula, South Shetland Islands ( Monniot and Monniot 1983). From 0 to 300 m depth .

Description

Globular colonies (55 and 85 mm height) with a wide short stalk totally covered with sand. Dark orange tunic. Zooids about 15 mm length with a six-lobed branchial siphon and a simple or tri-lobed atrial languet. We found 17 rows of stigmata with eight or ten stigmata per hemirow; there is a region of non-perforated membrane at both sides of the endostyle ( Figure 7b ). At the base of the thorax is a structure, possibly formed by reserve material, as observed in other Aplidium species. Stomach with five poorly marked folds. Ovaries below the gut loop; testes, both grouped or arranged in rows, only in the first half of the postabdomen. Characteristic larvae incubated in the tunic with three adhesive papillae, two of them closer in the dorsal region and the third more separate in the ventral region.

Remarks

This is the first record of this species since its description by Monniot and Monniot (1983). Although there is no doubt about the identification because of its characteristic larva and the shape and coloration of the colony, we have found some characteristics not mentioned in the holotype description. Firstly, the zooid size (15 mm) is smaller and the number of rows of stigmata (17) is fewer here, despite the colony sizes being similar, but this may be within the range of variation of the species. On the other hand, we observed a portion of non-perforated membrane at both sides of the endostyle ( Figure 7 ), a character not found by Monniot and Monniot (1983).

Aplidium radiatum ( Sluiter, 1906)

( Figure 8 )

Psammaplidium radiatum Sluiter, 1906 .

Sidnyum radiatum: Monniot F 1978 ; Monniot and Monniot 1983.

Macroclinum pererratum Sluiter, 1912, 1914 .

Sidnyum pererratum: Monniot F 1978 ; Monniot and Monniot 1983.

Aplidium circumvolutum (non Sluiter, 1900) parte Kott, 1969; Monniot and Monniot 1974. Aplidium radiatum :? Millar 1960;? Tatián et al. 1998a, 1998b; Sanamyan and Sanamyan 2002; Ramos Esplá et al. 2005.

Non Synoicum pererratum: Hartmeyer 1909 .

Distribution

New record: Bransfield Strait (Station B5: two specimens; Station B7: two specimens). Previously recorded: Antarctic Peninsula, Wilkes Land ( Monniot and Monniot 1983); South Shetland, South Orkney, and South Sandwich Islands ( Monniot and Monniot 1983, Tatián et al. 1998a, 1998b; Ramos-Esplá et al. 2005). From 25 to 500 m depth.

Description

Flattened colonies (from 15 to 97 mm), with dense sand over the surface and throughout the test. Zooids are not visible, but their location is marked by an elevation of the tunic; they form double-row systems. Zooids up to 5 mm, closely surrounded by the tunic. The oral siphon has eight pointed lobes while the atrial one has a narrow but thick tri-lobed languet. The branchial sac has 10–12 rows of stigmata, with quite high transverse vessels. The gut loop forms a much closed curve and the stomach has five well-marked folds. Unisexual zooids with the gonads immediately below the gut loop; they occupy most of the short postabdomen ( Figure 8a, b ).

We have considered as uncertain some samples that show variations with regard to the above description: oral siphon with only six lobes, low transverse vessels, longer oesophagus, and more marked stomach folds ( Figure 8c ).

Remarks

Aplidium radiatum closely resembles Aplidium circumvolutum ( Sluiter, 1900) and Aplidium imbutum Monniot and Monniot, 1983 . Aplidium imbutum is clearly distinguished by a thoracic filiform extension. However, the descriptions of A. circumvolutum and A. radiatum are practically identical. The absence of visible systems in the first one may be a consequence of the high density of incrusted sand, the difference in the number of oral lobes is not sufficient to separate the two species and, although most descriptions of A. circumvolutum mention the simultaneous presence of male and female gonads, Kott (1969) suggests that this may occur when gonads are not fully developed. The main problem is that very different descriptions have been provided for A. circumvolutum ; the type is lost and the few fragments of colonies (re-examined in the MNHN of Paris (registration number A1 SID-B 12 and A1 SID-B 13)) do not show the characteristics of the species. Even more, the holotype description of A. radiatum does not agree with the specimens to which it is referred ( Monniot F 1978).

Figures

Figure 7. Aplidium miripartum. (a) Zooid; (b) branchial sac with part of the membrane without stigmata; (c) larva.

Figure 8. Aplidium radiatum. (a) Female zooid; (b) male zooid; (c) doubtful zooid.