Sycettusa simplex ( Jenkin, 1908 )

Van, Rob W. M. & De, Nicole J., 2018, Calcareous sponges of the Western Indian Ocean and Red Sea, Zootaxa 4426 (1), pp. 1-160 : 119-122

Sycettusa simplex ( Jenkin, 1908)

Figs 73a–e , 74a–f

Grantessa simplex Jenkin, 1908: 446 , figs 93–97.

? Leuconia wasinensis ; Burton 1959: 181 (not: Jenkin 1908)

Material examined. RMNH Por. 10154, Maldives, Faafu Atoll, Wallstreet, 3.119°N 72.979556°E, depth 12 m, scuba, coll. N.J. de Voogd, field nr. MAD 10/MAS115, 20 February 2015; ZMA Por. 10338, Seychelles, Mahé, NE coast, Cap Maçons & Anse de Forbans, 4.7667°S 55.5167°E, reef, depth 0–6 m, snorkeling, coll. R.W.M. van Soest, field nr. NIOP-E stat. 612, 14 December 1992; ZMA Por. 12446, Seychelles, Amirantes, St. François Atoll, 7.0833°S 52.7333°E, reef, depth 0–10 m, snorkeling, coll. J.C. den Hartog, field nr. NIOP-E stat. 792(bis)/27, 4 January 1993.

Description. Light beige-colored groups of longer and/or shorter tubes ( Fig. 73a ), somewhat tangled, occasionally divided or with a side tube. Size of individual tubes up to 6 cm or more long, 0.5 cm wide. Surface uneven or slightly hispid. Oscules terminal, usually surrounded by a circle of diactines and/or trichoxeas. Beige color persists in alcohol ( Figs. 73b–c ). Consistency soft, slightly firm.

Aquiferous system. Syconoid.

Skeleton. ( Figs. 73d–e ) Inarticulate, with a cortical skeleton of regular or slightly sagittal triactines, subectosomal pseudosagittal triactines, the long paired actines forming the choanosomal skeleton together with the unpaired actines of subatrial sagittal triactines, and with an atrial skeleton of regular or slightly sagittal triactines smaller than those of the cortical skeleton. Diactines are present in the oscular region and also occur scattered in the choanosome supporting the inarticulated skeleton.

Spicules. ( Figs 74a–f ) Diactines, trichoxeas, cortical and atrial triactines, pseudosagittal triactines, sagittal triactines.

Diactines ( Fig. 74a ), fusiform, usually with one end lance-headed, variable in length, 210– 701 – 1140 x 13 – 25.8 –36 µm.

Trichoxeas ( Fig. 74b ), small, mostly broken, 120– 182 –235 x 2 – 2.4 –3.5 µm.

Cortical triactines ( Figs. 74c ), variable in shape, from equiangular equiradiate to sagittal or irregular, actines 183– 219 –288 x 12 – 17.4 –24 µm.

Pseudosagittal triactines ( Figs 74d ), in a large size range, longest actines 241– 369 –504 x 18 – 21.4 –30 µm, middle sized actines (usually the unpaired actine), 138– 186 –228 x 15 – 19.7 –30 µm, shortest actines 64– 132 –241 x 14 – 18.9 –26 µm.

Sagittal triactines ( Figs 74e ), variable in shape and in thickness, paired actines often almost forming T-shape, but occasionally more acutely angled, unpaired actines 396– 436 –538 x 17 – 29.6 –44 µm, paired actines 179– 232 –282 x 19 – 26.7 –39 µm.

Atrial triactines ( Fig. 74f ), regular, slightly sagittal or occasionally irregular, unpaired actine 114– 142 –181 x 10 – 11.4 –14 µm, paired actines 101– 154 –201 x 9 – 10.4 –12 µm.

Distribution and ecology. Maldives, Seychelles, Zanzibar, on reefs in shallow water.

Remarks. Jenkin’s type material is closely similar both in shape and spicule sizes and shapes. Our identification with his species is made with confidence.

The three samples assigned here to S. simplex have similar spiculation as S. stauridia described below. The differences between the two species appear to be largely attributable to growth form, which is known to be a variable feature in many sponges. In contrast, 28S sequences of the two species were found to be substantially different (cf. Fig. 3 ). Molecularly, S. simplex is almost identical to S. hastifera , as we found only a single site difference in the above described inspection of a trimmed alignment of 403 sites, whereas differences between S. simplex and S. stauridia numbered 22 sites.

Voigt et al. (2012) sequenced a Seychelles specimen, ZMA Por. 11566 under the name S. simplex , but we reidentified this material as S. zanzibarensis ( Jenkin, 1908) (see below).

Leucortis anguinea Ridley, 1884 from Providence in the Mascarene Islands is a Sycettusa according to Burton (1963). It has a shape reminding a bit of the present species, but the specimen is not likely the same as the present species judging from the description in Ridley 1884 (p. 629, pl. 53L, 54d), as it includes tetractines.

Sycettusa sibogae ( Burton, 1930) as redescribed by Van Soest & De Voogd (2015) is similar to the present species, but has no giant diactines and its cortical triactines are twice as large.

We reexamined Leuconia wasinensis sensu Burton, 1959 from South Arabia (Murray Expedition station 45 nr. 537) kept in the Natural History Museum (BMNH 1936.3.4.537) and found this to be very similar to Sycettusa simplex . Its identity cannot be Leucandrilla wasinensis as it has a smooth tubular shape, not oval and hispid; it lacks an apical fringe and its skeleton is inarticulate. The subcortical triactines are pseudosagittal and both cortical and atrial skeleton consist of smaller triactines.

Figures

FIGURE 3. Maximum-likelihood tree based on analysis of sequences of the partial 28S gene (C2–D2 region, comprising 461 sites) of Western Indian Ocean Calcaronea newly generated by the Naturalis Biodiversity Center and sequences additionally obtained from GenBank, the Sponge Barcode Project and from Oliver Voigt (München) from the Red Sea, Indonesia, Australia, and a few sequences from other parts of the world, to demonstrate the affiliation of the compared species. Numbers at the root of clades are bootstrap values of 1000 replicates.

FIGURE 73. Sycettusa simplex (Jenkin, 1908), a–c, habitus of RMNH Por. 10154 from the Maldives, a, habitus in situ (photo N.J. de Voogd), b, on deck (photo N.J. de Voogd), c, preserved (scale bar = 1 cm), d, light microscopic image of cross section, e, detail of the same.

FIGURE 74. Sycettusa simplex (Jenkin, 1908), RMNH Por. 10154, from the Maldives, a–f, SEM images of the spicules, a, lance-headed giant diactine, b, broken trichoxea, c, cortical triactines, d, pseudosagittal triactines, e, sagittal subatrial triactines, f, atrial triactine.