Desdemona Banse, 1957  

Desdemona Banse, 1957

Desdemona? sp. 1

Voucher. SEA LION: station 3MFC (with branchial crown, non-brooding); station 22 MFA (with branchial crown, brooding) and station 56MFB (branchial crown missing).

Diagnosis (based on voucher from station 3MFC). Small, extremely slender species; voucher is a complete specimen with branchial crown; body 3.8 mm long and 0.15 mm wide, branchial crown is 0.5 mm long; body with 8 thoracic and 15 abdominal segments; posterior thoracic and anterior abdominal segment elongated (much longer than wide); posterior abdominal segments short again; colour in alcohol pale yellow.

Branchial crown with 3 pairs of radioles and 1 pair of shorter non-vascularized ventral filaments; radioles with 5 or possibly 6 pairs of widely separated pinnules.

Collar is well-developed; much higher ventrally (=anterior margin of anterior peristomial ring developed ventrally as wide lobe); low dorsally with two deep dorso-lateral notches; well developed, long, narrow dorsal lip observed.

Glandular ridge on chaetiger 2 present. Peristomial eyes not observed.

Superior thoracic notochaetae long, limbate; inferior thoracic notochaetae short, simple capillaries. Thoracic neurochaetae acicular; with at least 5 teeth decreasing in size above the main fang; reducing in number from 10 in chaetiger 2 to 3 in chaetiger 8 (the last thoracic chaetiger). Abdominal uncini avicular with enlarged breast; the number constant, with 6 in chaetiger 9 and 5 posteriomost chaetigers, but the last one which only bears 1 uncinus. Anterior abdominal uncini extremely small; anterior one very narrow, arranged in about 3 rows (in frontal view), with about 6 teeth per row; posterior uncini broader, arranged in about 5 rows (in frontal view).

Posteriomost chaetigers gradually narrowing into well developed, rounded, triangular to cordiform pygidial lobe, terminal cirrus or pygidial eyespots not observed. Tube not observed.

Reproduction. In several specimens a single small juvenile was found inside the branchial crown and these specimens appear to have longer and perhaps more numerous pinnules on their radioles than voucher from station 3MFS. At present, we assume this to be an adaptation that enables brooding of juveniles. No other morphological differences were observed. Brooding of eggs and larvae within the branchial crown has been linked to small body size and habitat. Of other Sabellidae known from the region, this strategy has been documented in Perkinsiana antarctica (Knight-Jones and Bowden, 1984; Gambi and Patti, 1999) and Myxicola cf. sulcata (Gambi et al., 2001).

Remarks. The small size, relatively low number of abdominal segments, development of collar, lack of inferior mucronate chaetae and form of thoracic and abdominal uncini suggest these Falkland Is. specimens belong to the genus DesdemonaBanse, 1957. However, there are also some inconsistencies, such as lack of peristomial or pygidial eyes and the number of abdominal segments while relatively low is higher (N=15) than in all other know species (up to 8).

This is a small genus, currently with five valid species, all with Southern Hemisphere distribution. Three of these are reported from the area - D. trilobata (with type locality: Falkland Islands), D. nova and D. antarctica. Should the generic identification be confirmed by subsequent work, specimens from Falkland Islands collected here likely represent a new species.

Overview of known Desdemona species:

D. ornata: radioles with dark pigments, collar missing dorsally, with 8 abdominal segments only.

D. trilobata: presence of two pairs of obvious persistomial eyes; only 6 abdominal segments and pair of lateral wings in posteriormost abdominal segments.

D. antarctica: presence of small pair of peristomial eyes, collar with a single dorsal incision only, with 7 abdominal segments only.

D. nova ? 

D. aniara: collar similar to D. antarctica, radioles with 8 pairs of pinnules.