Sigillina exigua, Kott, 2006

Kott, Patricia, 2006, Observations on non-didemnid ascidians from Australian waters (1), Journal of Natural History 40 (3 - 4), pp. 169-234: 184-189

publication ID

http://doi.org/ 10.1080/00222930600621601

persistent identifier

http://treatment.plazi.org/id/011D87C1-FFE3-CD57-1FD4-FD5DE1ADFD23

treatment provided by

Felipe

scientific name

Sigillina exigua
status

sp. nov.

Sigillina exigua   sp. nov.

( Figures 2A–C View Figure 2 , 8D View Figure 8 )

Distribution

Type locality. South Australia (Kangaroo I., ‘‘ The Arches’ ’, Western River , on rock wall, 10–12 m, coll. K. Gowlett Holmes, 10 December 1999, syntypes SAM E3300 View Materials )   .

Description

Colonies are small flat-topped cushions, about 2 cm diameter and to 5 mm high attached to calcareous debris. Zooids open on the upper surface. The test is soft and transparent. Zooids are short, about 3 mm long, the thorax, abdomen and posterior abdomen being each about equal in length. A short vascular stolon is at the posterior end of the body. Both six-lobed apertures are on the anterior end of the thorax.

Three long rows of stigmata are in the branchial sac. Gonads are in the abdomen. A large almost spherical brood pouch constricted off from the postero-dorsal corner of the thorax contains a single embryo.

The larval trunk is spherical and 1.1 mm diameter. An otolith and ocellus and three rows of stigmata are in the oozooid. Two large flat-topped adhesive organs, each in a thin-walled epidermal cup and with a short thick stalk, are depressed into the trunk in the anteromedian line. Three large median ectodermal ampullae alternate with the adhesive organs and curve around their stalks. The tail winds completely around the trunk.

Remarks

The cushion-like colonies and the zooids are particularly small for this genus. The species most closely resembles S. signifera   , having flat-topped colonies and two large adhesive organs. However, both zooids and larvae of the present species are smaller ( S. signifera   larvae having a trunk 0.5 mm long). The present species from the southern Atlantic may be a sister species isolated from S. signifera   which has a wide range and is common in tropical waters.

The separately opening zooids, large larval trunks, wide, flat-topped, thick stalked larval adhesive organs, the three long rows of stigmata and the postero-dorsal thoracic brood pouch are characteristic of both this genus and Pseudodistoma   , which is distinguished by its long posterior abdomen containing the gonads and the lack of the posterior abdominal vascular stolon of Sigillina   . Kott (1992a) overlooked the similarity of Sigillina   and Pseudodistoma   and, although she later ( Kott 1998, 2005b) emphasized the remarkable, large larval adhesive organs in Pseudodistoma   , she again overlooked their likeness to the adhesive organs of Sigillina   . It is possible the relationship of Sigillina   to the Holozoidae   based on the pattern of replication from the large vascular stolon (see Caullery 1909) could be less important than it previously was thought to be; and that the presence of the gonads in a posterior abdomen with conspicuous bands of longitudinal muscles along each side (that distinguishes Pseudodistomidae   from Sigillina   ) may be less compelling than the characters (listed above) that are shared by these genera and suggest a closer phylogenetic relationship than previously was proposed.

Distaplia australiensis Brewin, 1953  

( Figure 8E, F View Figure 8 )

Distaplia australiensis Brewin 1953, p 61   . Kott 2003, p 1619 View Cited Treatment and synonymy (part, not specimens from Queensland 5 Distaplia turboensis Kott 2004, p 45   ).

Distribution

Previously recorded (see Kott 2003 and D. turboensis Kott, 2004   ): South Australia (Spencer Gulf, Gulf St Vincent, Bass Strait, D’Entrecasteaux Channel, Huon Channel. New records: South Australia (Kangaroo I., 4–7 m, SAM E3294–5).

Description

Long cylindrical stalks each with a soft, rounded head surrounded by parallel double rows of zooids extending from the top of the stalk to a terminal common cloacal aperture. Zooids have the usual large atrial aperture opening directly into the vertical common cloacal canal between each row of zooids of the pair. The stomach wall has about 16 parallel longitudinal pleats. Gonads were not detected in the newly recorded colonies, although usually they are in a sac separated from the abdomen by a narrow constriction.

Remarks

Although the arrangement of the zooids in long vertical rows and the presence of the gonads in a posterior abdomen is similar to the tropical Distaplia turboensis   , the present species is distinguished by its long cylindrical stalks and fewer stomach folds.

Distaplia florida Kott, 1990  

( Figure 8G View Figure 8 )

Distaplia florida Kott 1990a, p 118   .

Distribution

Previously recorded (see Kott 1990a): South Australia (Great Australian Bight); Victoria (King I.); New South Wales ( Byron Bay ). New records: Victoria (Flinders Pier, QM G308566)   ; Tasmania (Tasman Peninsula, 15–18 m, SAM E3293 View Materials ; Port Davey , 6–8 m, SAM E3233 View Materials )   .

Description

Colonies are soft, hemispherical or cushion-shaped (up to 3 cm diameter) to flat encrusting sheets with circular to elongate systems of zooids around large circular common cloacal apertures, about 5 mm apart. They are beige in preservative, and minute crystalline particles in the test give it a cloudy appearance. In the preserved specimens, radial furrows around the common cloacal apertures may be the result of preservation and/or contraction. A shallow concavity in the surface over each circular common cloacal cavity has its margin overhung by the surrounding surface test. Branchial apertures open beneath this overhang. The atrial apertures are large sessile openings around the common cloacal cavity with their anterior lips extending out into the margin of the common cloacal aperture. Black faecal pellets in the base of the circular common cloacal cavities are conspicuous from the surface. About 10 zooids surround each common cloacal cavity.

Zooids have a long oesophageal neck, a smooth stomach wall and gonads in the gut loop. Four rows of about 25 stigmata are each crossed by a parastigmatic vessel. A vegetative stolon projects into the base of the colony.

Remarks

Species of Distaplia   are difficult to distinguish from one another, often having circular systems and soft cloudy test like the present one. The presence or absence of a posterior abdomen is a useful character but, when zooids are immature as in the present case, the smooth stomach wall helps to distinguish this species from others in which it is folded. The concavities over each common cloacal cavity in the preserved specimens appear to be characteristic of this species, although both species have circular systems, smooth stomachs and gonads in the gut loop. The present species is distinguished from Distaplia viridis Kott, 1957   by the more numerous branchial stigmata, and by its colour.

Distaplia pallida Kott, 1990  

( Figure 8H View Figure 8 )

Distaplia pallida Kott 1990a, p 121   .

Distribution

Previously recorded (see Kott 1990a): South Australia (Great Australian Bight, Gulf St Vincent); Victoria (Portsea); New South Wales ( Byron Bay ); Tasmania (Tinderbox). New records   : Tasmania ( Port Davey , 5–7 m, SAM E3273 View Materials )   .

Description

The colony is a firm, jelly-like translucent cushion with conical lobes protruding from the upper surface. Zooids are arranged in circular to long oval systems around sessile common cloacal openings. Sometimes the common cloacal apertures are long slits between two apparently parallel rows of zooids, and at each end the opening extends into narrow slits in the roof of the common cloacal canal that expose the atrial apertures directly to the exterior. The translucent internal or basal test contains criss-crossing posterior stolons of the zooids. About 12 stigmata are in each row in the branchial sac and the stomach has about 10 broad, parallel external folds. Gonads were not detected in the newly recorded specimens, although in previously recorded specimens they are reported to be in the gut loop. Photographs show colonies as pale blue, although they are beige in preservative.

Remarks

The species is distinguished from other species with circular to longitudinal systems by its relatively few branchial stigmata, broad stomach folds, and gonads in the gut loop (see Kott 1990a).

Sycozoa murrayi ( Herdman, 1886)  

Colella murrayi Herdman 1886, p 115   .

Sycozoa murrayi: Kott 1990a, p 146   and synonymy.

Distribution

Previously recorded (see Kott 1990a): South Australia (Great Australian Bight, Gulf St Vincent); Tasmania (MidwayPoint,NETasman);NSW(Bermagui).Newrecords:Tasmanian Canyons (King I. Canyon, 248–249 m; Banks Strait, 168.4 m; Big Horseshoe —west band, 159.6 m; Ling Hole, 163 m; Pieman Canyon, 173.8–176 m; 40.77531 ° E, 144.22719 ° S, 94.6 m)   .

Description

The species has relatively firm spatulate to fan-shaped heads on short fleshy stalks which contain the long posterior abdominal stolons characteristic of this genus. Colonies are yellow in deck photographs, however its living colour is not known. The zooids are immature in these specimens which were collected in April.

Remarks

The species previously has been recorded from depths similar to those newly recorded (e.g. Herdman 1886 off Bermagui and in Bass Strait at 200–250 m). The fan-shaped head sometimes observed in the present species resembles that of S. brevicauda Kott, 1990   , although the latter species had a longer, narrower and less fleshy stalk.

Sycozoa sigillinoides Lesson, 1830  

Sycozoa sigillinoides Lesson 1830, p 436   . Kott 1990a, p 153 and synonymy.

Distribution

Previously recorded (see Kott 1990a): South Australia (S. Spencer Gulf); Tasmania (St Helen’s and Montague I.). Magellanic area ; Falkland Is ; Kerguelen , Heard I.; Macquarie I.; Chatham I.; New Zealand and the Antarctic. New records: Tasmania (Tasman Peninsula, 20–22 m, SAM E3247 View Materials )   , Tasmanian Canyons (King I. Canyons, 249 m; Banks Strait, 168 m; Ling Hole, 163 m, 174 m; Pieman Canyon, 173–176 m).

Description

The newly recorded specimen from the Tasman Peninsula is a stiff, narrow stalk, with stiff annular thickenings at intervals. It has two short terminal branches, each bearing a small mushroom-shaped head with vertical double rows of zooids and a terminal common cloacal aperture.

Remarks

Australian records of this species are few, but the new records are from Tasmania within the range previously recorded. The newly recorded specimens (taken in April) are either long wiry headless stalks or stalks with very small (regenerating) heads. Millar (1960) reported headless stalks in May, June, and July; stalks with regenerating heads in December, March, May, June, and July; and sexual reproduction at its peak in March. The regenerating post-reproductive stalks of the newly recorded specimens (taken in April) are within this timeframe. The presence of isolated heads of this species in the plankton of the tropical Atlantic and Pacific (see Kott 1990a) has already been reported.

SAM

South African Museum

QM

Queensland Museum

Kingdom

Animalia

Phylum

Chordata

Class

Ascidiacea

Order

Aplousobranchia

Family

Holozoidae

Genus

Sigillina

Loc

Sigillina exigua

Kott, Patricia 2006
2006
Loc

Distaplia florida

Kott P 1990: 118
1990
Loc

Distaplia pallida

Kott P 1990: 121
1990
Loc

Sycozoa murrayi:

Kott P 1990: 146
1990
Loc

Distaplia australiensis

Kott P 2004: 45
Kott P 2003: 1619
Brewin BI 1953: 61
1953
Loc

Colella murrayi

Herdman WA 1886: 115
1886
Loc

Sycozoa sigillinoides

Kott P 1990: 153
Lesson RP 1830: 436
1830