Tetrazona ciemari, Primo & Vázquez, 2007

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 : 1793-1797

Tetrazona ciemari sp. nov.

( Figures 15 , 16 )

Distribution

New record: Bransfield Strait (Station B 6: one specimen; Station B 7: two specimens). From 138 to 142 m depth. Holotype: MNCN 31.01 /78, Museo Nacional de Ciencias Naturales , Madrid ( Spain).

Description

Small colonies (up to 24 mm of maximum length), rounded but flattened ( Figure 15 ). The tunic is rather soft, resistant and practically free from sand, except for some dispersed particles inserted irregularly among the zooids. The zooids are scattered without apparent order for the whole colony.

The zooids measure 4 mm on average, the abdomen being a little shorter than the thorax. Both siphons are tubular and six-lobed, the atrial one slightly longer. They are located at the same level on the dorsal part. There are about 20 simple branchial tentacles of several sizes. The branchial sac has four rows of about 20 stigmata per semi-row, without parastigmatic vessels ( Figure 16b ). The first two rows are smaller. The languets of the dorsal lamina are long and pointed.

The short oesophagus ends in a globular smooth-walled stomach, quite voluminous and clearly separated from the gut loop that forms an open curve. The anus opens in the middle of the thorax. A vascular appendix is present at the level of the gut loop.

There are no developed gonads, but we observed the sperm duct in the lower part of the thorax of some zooids and the presence of small oocytes in the basal part of the abdomen ( Figure 16a ). There are no larvae.

Remarks

The genus Tetrazona was created by Michaelsen (1930) to include those species close to Cystodytes , but without calcareous spicules. Currently, only two species of this genus are known: T. porrecta Millar, 1962 and T. glareosa ( Sluiter, 1906) .

Tetrazona porrecta is a South African species that differs both in the colony structure (upright, long and narrow, with irregular lobes and protuberances) and in the zooids, with a similar size but with an abdomen longer than the thorax, fewer stigmata, folds on the stomach wall and gonads immediately below the lower bend of the gut loop. Furthermore, we have had access to a specimen from South Africa (collected by the Coral Reef Research Foundation), so we can affirm that this is not the same species.

On the other hand, we examined some specimens deposited at the MNHN of the Antarctic species T. glareosa , and it presents a similar structure of the colony. However, there are important differences. First, T. glareosa has asterisk-like spicules irregularly scattered in the tunic; although Kott (1969) commented that these spicules, described by Sluiter (1906) as siliceous, could be artefacts of preservation, Monniot and Monniot (1983) and Tatián et al. (2005) found this species again and described calcareous spicules. Another significant difference is the size of the zooids, up to 2 mm, which seems to be a constant character independently of the colony size in T. glareosa , and up to 4 mm in our specimens. Also, while in T. glareosa the proportion thorax/abdomen is similar, in our specimens the thorax is always longer, sometimes twice the size of the abdomen. Another difference is the number of oral tentacles: 12 in the specimens of T. glareosa described by Sluiter (1906) and only four in those described by Monniot and Monniot (1983), short and pointed in both cases, while we have found 20 longer oral tentacles. As for the gut loop, there is no net transition between stomach and intestine in T. glareosa , whereas it exists in our specimens. Finally, Monniot and Monniot (1983) mentioned long postabdominal vascular appendix, crossed in every direction in the tunic; however, instead of these prolongations, we found a relatively long vascular appendix close to the gut loop.

Family CIONIDAE

Tylobranchion speciosum Herdman, 1886

Tylobranchion speciosum Herdman, 1886 ; Arnback-Christie-Linde 1926; Kott 1954, 1969, 1971; Millar 1960, 1968; Vasseur 1974; Monniot and Monniot 1974, 1983, 1994; Monniot C 1978; Tatián et al. 1998a, 1998b, 2005; Ramos-Esplá et al. 2005; Arntz et al. 2006.

Tylobranchion antarcticum Herdman, 1902 ; Sluiter 1906, 1914; Hartmeyer 1911; Arnback- Christie-Linde 1926, 1950; Van Name 1945.

Tylobranchion weddelli Arnback, 1926 ; Arnback-Christie-Linde 1950.

Pharyngodictyon reductum Sluiter, 1906 ; Van Name 1945; Kott 1969.

? Stereoclavella antarctica Herdman, 1910 .

Distribution

New record: Bransfield Strait (Station B5: five specimens 28–50 mm height). Previously recorded: Antarctic Region ( Millar 1960, 1968; Kott 1969; Monniot and Monniot 1983; Ramos-Esplá et al. 2005); South Georgia ( Tatián et al. 1998a, 1998b, 2005); Bouvet Island ( Arntz et al. 2006); Kerguelen Island ( Monniot C 1978); Magellan Strait ( Monniot and Monniot 1983). From 25 to 437 m depth, although it has also been collected at 2897 m ( Kott, 1971).

Description

Our specimen agrees with the description by Kott (1969).

Remarks

Three Tylobranchion Antarctic species were described in function of their different size, stomach folds, and the shape of musculature and papillae ( Arnback-Christie-Linde 1950). They were synonymized by Kott (1954), supported by Millar (1960) who found that these characters overlap. Monniot and Monniot (1983) considered the problem still unresolved,

but they admitted that these differences might be due to age or physiological stage of the colony.

Family CORELLIIDAE

Corella eumyota Traustedt, 1882

Corella eumyota Traustedt, 1882 ; Traustedt 1885; Herdman 1891, 1910; Michaelsen 1898, 1900, 1907, 1915, 1918, 1922, 1934; Sluiter 1898, 1914, 1932; Hartmeyer 1911, 1913, 1920; Bovien 1922; Arnback-Christie-Linde 1929, 1938; Van Name 1945; Brewin 1946, 1948, 1950, 1951, 1952, 1956, 1957, 1958, 1960; Kott 1952, 1954, 1969, 1971, 1985, 1997; Millar 1955a, 1960, 1962, 1966, 1967, 1968, 1982; Vinogradova 1962; Monniot C 1969 –70, 1978; Monniot and Monniot 1974, 1983, 1994; Turón 1988; Lambert et al. 1995; Tatián et al. 1998a, 1998b; Sanamyan and Sanamyan 1999, 2002; Monniot et al. 2001; Lambert 2004; Ramos-Esplá et al. 2005.

Corella novarae Drasche, 1884 .

Corella japonica non Herdman, 1880: Sluiter, 1900.

Corella antartica Sluiter, 1905 ; Sluiter 1906.

Corella benedeni Beneden and Longchamps, 1913 ; Arnback-Christie-Linde 1938.

Corella dohrni Beneden and Longchamps, 1913 ; Herdman 1923; Arnback-Christie-Linde 1938.

Distribution

New record: Bransfield Strait (Station B5: 14 specimens (36–160 mm height); Station B6: one specimen; Station B7: three specimens). Previously recorded: widely distributed in the Southern Hemisphere ( Kott 1969); north-western France ( Lambert 2004). From 7 to 1376 m depth.

Description

Our specimens coincide with those described by Kott (1969).

Family ASCIDIIDAE

Ascidia challengeri Herdman, 1882

Ascidia challengeri Herdman, 1882 ; Herdman 1891, 1923; Arnback-Christie-Linde 1938; Van Name 1945; Kott 1954, 1969, 1971, 1985; Millar 1960, 1968, 1970; Vinogradova 1962; Monniot and Monniot 1974, 1982, 1983, 1994; Monniot C 1978; Turon 1988; Tatián et al. 1998a, 1998b; Ramos-Esplá et al. 2005.

Ascidia vasculosa Herdman, 1880 ; Herdman 1882?

Ascidia despecta Herdman, 1880 ; Herdman 1882.

Ascidia placenta Herdman, 1880 ; Herdman 1882, 1923.

Ascidia charcoti Sluiter, 1905 ; Sluiter 1906; Herdman 1912, 1915, 1923.

Phallusia charcoti: Hartmeyer 1911 ; Hartmeyer 1912; Sluiter 1914.

Phallusia challengeri: Hartmeyer 1912 .

Ascidia dispar Arnback, 1938 .

Ascidia meridionalis Kott, 1954 ?; Kott 1969.

Ascidia parameridionalis Vinogradova, 1962 .

Ascidia tenera Monniot and Monniot, 1974 .

Distribution

New record: Bransfield Strait (Station B4: three specimens; Station B5: 15 specimens; Station B6: four specimens; Station B7: five specimens. From 20 to 210 mm height). Previously recorded: Antarctic Region ( Kott 1969; Millar 1960; Monniot and Monniot 1983; Tatián et al. 1998a, 1998b; Ramos-Esplá et al. 2005); Kerguelen and Heard Islands ( Vinogradova 1962); Tasmania ( Kott 1985); Namibia ( Turon 1988). From 7 to 2350 m depth.

Remarks

Although species of the genus Ascidia can be difficult to distinguish, only three species are recognized from the Antarctic Region. Ascidia translucida Herdman, 1880 is clearly distinct because of its size (see Table II), and because the dorsal tubercle fills the peritubercular area and is very convoluted, while Ascidia challengeri Herdman, 1882 and Ascidia meridionalis Herdman, 1880 are more similar. We summarize distinguishing characters in Table II.

Figures

Figure 15. Tetrazona ciemari sp. nov., colonies.

Figure 16. Tetrazona ciemari sp. nov. (a) Zooid; (b) zooid with open thorax.