Sycettusa zanzibaris ( Jenkin, 1908 )
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|Sycettusa zanzibaris ( Jenkin, 1908 )|
Grantessa zanzibaris Jenkin, 1908: 448 , figs 98–102; Burton 1959: 180.
Material examined. ZMAAbout ZMA Por. 11491, Seychelles, Bird Island, off E coast, 3.7167°S 55.2167°E, reef, depth 3 m, snorkeling, coll. R.W.M. van Soest, field nrGoogleMaps . NIOP-E stat. 717/ 08, 20 December 1992; ZMAAbout ZMA Por. 11566, Seychelles, Amirantes, Île Desnoeufs platform, outer slope, 6.2167°S 53.0167°E, depth 12–15 m, scuba, coll. R.W.M. van Soest, field nrGoogleMaps . NIOP-E stat. 738/ 22, 2 January 1993; ZMAAbout ZMA Por. 11568, Seychelles, Amirantes, N of D’Arros Island, 5.4°S 53.3167°E, depth 45–55 m, on rhodolite bottom, dredge, coll. R.W.M. van Soest, field nrGoogleMaps . NIOP-E stat. 752/ 13, 26 December 1992; ZMAAbout ZMA Por. 12438, Seychelles, Amirantes, N of D’Arros Island, 5.4°S 53.3167°E, depth 45–55 m, on rhodolite bottom, dredge, coll. R.W.M. van Soest, field nrGoogleMaps . NIOP-E stat. 752/ 11, 26 December 1992.
Description. Masses of short tubes ( Figs 77a–b View Figure ), beige-white to light brown in situ and on deck, pale transparent white in alcohol. The specimens have a quite characteristic glassy slippery appearance in alcohol. Size of largest mass up to 2 cm in lateral expansion, 1–2 cm high. Individual tubes up to 5 mm high, 3–4 mm in diameter, with the oscule about 1 mm diameter and surrounded by a thin collar. Consistency cartilaginous.
Aquiferous system. Syconoid.
Skeleton. ( Figs 77c–g View Figure ) Inarticulate ( Figs 77c–d View Figure ). The cortical skeleton ( Fig. 77e View Figure ) is a mixture of tangential triactines and short banana-shaped diactines, carried by the shortest paired actine and unpaired actine of subcortical pseudosagittal triactines. The inarticulate skeleton is made up of the longer actines of the subcortical pseudosagittal triactines and the unpaired actines of subatrial triactines. The atrial skeleton ( Fig. 77f View Figure ) consists of the paired actines of the subatrial triactines supported by two types of tetractines, smaller with all actines of almost similar length and thickness, and larger with enlarged apical actines protruding far into the atrial lumen. The small oscular collar ( Fig. 77g View Figure ) is formed by giant diactines, trichoxeas, triactines (similar to the subatrial triactines) and regular tetractines with a short apical actine.
Spicules. ( Figs 78a–i View Figure ) Diactines, trichoxeas, cortical triactines, pseudosagittal triactines, sagittal triactines, tetractines.
Giant diactines( Fig. 78a View Figure ), fusiform 402– 667 – 1100 x 12 – 20.6 –29 µm.
Trichoxeas (Fig, 78b), invariably broken, fragments 240–330 x 2–3 µm.
Banana-shaped diactines ( Fig. 78c View Figure ), curved, asymmetrical, 141– 162 –204 x 7 –8.1–9 µm.
Cortical triactines ( Figs 78d View Figure ), equiangular and equiradiate or more often with all actines of slightly different length or slightly sagittal, actines 84– 103 –126 x 6 – 8.3 –10 µm.
Pseudosagittal triactines ( Figs 78e View Figure ), with middle actine straight or gently curved, and shortest actine with a characteristic angular curve, longest actines 81– 146 –183 x 6 – 6.9 –8 µm, middle-sized actines 73– 106 –138 x 6 – 6.6 –9 µm, shortest (unpaired) actines 59– 88 –111 x 6 – 6.8 –8 µm.
Subatrial triactines ( Figs 78f View Figure ) (and triactines of the oscular collar), sagittal, almost T-shaped, unpaired actines
151– 179 –210 x 8 – 9.8 –11 µm, paired actines 81– 92 –105 x 7 – 8.2 –9 µm. Small equiradiate tetractines ( Fig. 78g View Figure ), equiangular, but not equiradiate, with clear position of unpaired actines, paired actines and curved apical actines; unpaired actines 54– 69 – 84 x 5 – 6.3 –8 µm, paired actines 76– 97 –111 x 6 – 6.7 –7 µm, apical actines 37– 56 – 84 x 5 – 5.7 –7 µm.
Larger atrial tetractines ( Fig. 78h View Figure ), unpaired and paired actines similar in length, 62– 95 –112 x 5 –6.6–8 µm, apical actines long, curved or sometimes slightly crooked, 105– 229 –432 x 6 – 7.1 –9 µm.
Tetractines of the oscular collar ( Fig. 78i View Figure ), resembling subatrial sagittal triactines but with small curved apical actine; unpaired actines, 81– 112 –126 x 7 – 7.4 –9 µm, paired actines 84– 96 –111 x 7 –7.6–9 µm, apical actines 22– 43 – 61 x 5 – 5.7 –7 µm.
Distribution and ecology. Seychelles, Zanzibar, shallow water down to 55 m. Burton (1959) reported this species from the Southern Red Sea, but provided no description.
Remarks. The presence of tetractines and the characteristic angular curve of the unpaired actines of the pseudosagittal triactines distinguish this species from all other Sycettusa species of the Western Indian Ocean.
Voigt et al. (2012) used ZMAAbout ZMA Por. 11566 for their study of the phylogeny of Calcarea (identified as S. cf. simplex ). Voigt et al. ’s sequence was compared with our own from ZMAAbout ZMA Por. 11568 (see Fig. 74 View Figure ), and in an alignment trimmed to a length of 403 sites, we found two differences. Our partial 28S sequences of Sycettusa zanzibaris grouped in the same clade together with New Caledonian S. tenuis Borojević & Klautau, 2000 (downloaded from the Sponge Barcode Project site) away from mainstream Sycettusa species and closer to Grantessa species. S. zanzibaris and S. tenuis were found to exhibit 3 differences in the 403 sites alignment, so these are probably closely related. Borojević & Klautau 2000 (p. 198) stated in their remarks that S. tenuis was ‘certainly close to Sycettusa simplex ( Jenkin, 1908) ’, but as these authors admit, S. simplex has no tetractines (cf. Jenkin’s description of the atrial skeleton and spicules on p. 449). Remarkably, they did not point out that S. zanzibaris rather than S. simplex is the closer species.
The position of the group of species comprising Ute , Uteopsis and Grantessa grouped in our phylogeny of Fig. 3 View Figure within the larger clade of Sycettusa species remains unclear for the moment.
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