Didemnum psammatode ( Sluiter, 1895 )

Kott, Patricia, 2007, New and little-known species of Didemnidae (Ascidiacea, Tunicata) from Australia (part 4), Journal of Natural History 41 (17 - 20), pp. 1163-1211 : 1190

Didemnum psammatode ( Sluiter, 1895)

( Figures 9H , 10 A–C)

Leptoclinum psamathodes Sluiter 1895, p 171 .

Didemnum psammatode: Kott 2001, p 229 and synonymy; 2004c, p 40 and synonymy.

Distribution

Previously recorded (see Kott 2002): Australia (tropical and temperate locations); Indian Ocean ( Red Sea , Sri Lanka); Western Pacific ( Indonesia, Philippines); Japan; China. New records: Tasmania (McGuiness Gutter, 6 m, QM G308831 ) ; Queensland (Great Barrier Reef, 18.015 ° S, 146.295 ° E, 25 m, QM G308879 ; 14.685 ° S, 145.535 ° E, 30 m, QM G308820 ) .

Description

Kott (2001) noted the variability in the small spicules (to 0.035 mm diameter), some being stellate with 11–13 short conical rays while others are burr-shaped with rod-shaped to fusiform or paddle-shaped rays. The newly recorded specimens from the northern Great Barrier Reef to Tasmania reflect this variation, although, unlike the specimen from the Capricorn Group (QM G308143, see Kott 2001, Figure 168A) with a mixture of burr-like spicules with rod-shaped rays to stellate spicules, the full range of spicules is not present in any one of the newly recorded colonies. A specimen from the northern Great Barrier Reef (QM G308820, see Figure 10A, B ) and another (an epibiont on Polycarpa flaυa) from Tasmania (QM G308831, see Figure 10C ) have stellate spicules with only 9–11 rays. However, another specimen from the northern Great Barrier Reef (QM G308879) has exclusively burr-shaped spicules with rod-shaped rays (see Figure 9H ). These spicules are all less than 0.05 mm diameter and the small zooids and the colonies all fall within the parameters reported for the species.

Remarks

Some species of Trididemnum are reported to have faeces pellets embedded in the basal test. The only other species in which this condition has been observed are Didemnum corium Kott, 2005a and the present species. Didemnum corium is distinguished by its large spicules (to 0.1 mm diameter with seven to nine robust pointed rays in optical transverse section) and their even distribution in the surface and base of the colony and lining the deep primary posterior abdominal common cloacal cavities.

Figures

Figure 9. Scanning electron micrographs. (A) Didemnum membranceum (QM G308854); (B) Didemnum microthoracium (SAM E3259); (C) Didemnum moseleyi (QM G308866); (D) Didemnum parau (QM G308859); (E) Didemnum patulum (QM G308769); (F) Didemnum pellucidum (QM G308886); (G) Didemnum perplexum (QM G308860); (H) Didemnum psammatode (QM G308879).

Figure 10. Scanning electron micrographs. (A–C) Didemnum psammatode [(A, B) QM G308820; (C) QM G308831]; (D) Didemnum tantalum (QM G308860); (E) Didemnum tumulatum (QM G308873); (F) Didemnum υesica (QM G308875); (G) Didemnum υiride (QM G308864); (H) Trididemnum farrago (QM G308819).