Ascandra kakaban, Van Soest & De Voogd, 2015

Ascandra kakaban View in CoL sp.nov.

Figures 24a–e View FIGURE 24 , 25a–e View FIGURE 25

Material examined. Holotype RMNH Por. 1696, Indonesia, Kalimantan, Berau Islands, Kakaban island , 2.1409°N 118.5112°E, depth 0.5 m, snorkeling, coll. N.J. de Voogd, #BER08/121003/123, 12 October 2003. GoogleMaps

Paratype RMNH 4625 About RMNH , Indonesia, East Kalimantan Province, Berau Region, kakaban island, Kakaban marine lake, 2.4133°N 118.5078°E, depth 0–2 m, snorkeling, coll. L.E. Becking GoogleMaps , # LE043 , 31 August 2008 .

Description. The cormus ( Figs 24a–c View FIGURE 24 ) consists of a single (holotype, Fig. 24a View FIGURE 24 ) or several (paratype, Fig. 24b View FIGURE 24 ) wide semi-transparent tubes, which are probably water collecting tubes, issuing from a network of relatively few thinner tubes. In some, possibly ageing, individuals, like the holotype, these tubes at their base proliferate into a cluster of intertwined ‘blind’ tubules, more brightly white colored, but in other individuals (paratype) this is less developed. Size of the cormus in preserved condition ( Figs 24d–e View FIGURE 24 ) up to 7.5 x 7 x 3 cm, largest fragment 4 x 3.5 x 3 cm ( Fig. 24e View FIGURE 24 ).

Skeleton. ( Figs 25a–b View FIGURE 25 ) The wall of the tubes is built of a thin layer of triactines and tetractines ( Fig. 25a View FIGURE 25 ), with the apical actines of the tetractines directed into the tubar lumen ( Fig. 25b View FIGURE 25 , arrows).

Spicules. ( Figs 25c–e View FIGURE 25 ) Triactines, tetractines.

Triactines ( Figs 25c View FIGURE 25 ), equiangular equiactinal, in a large size range, possibly divisible in two overlapping size classes, actines thinly conical, tapering to sharp apices, overall length of actines, 57– 154.0 –220 x 4– 9.4 –12 µm.

Tetractines ( Figs 25d View FIGURE 25 ), similar in shape to triactines but distinctly larger, actines of the basal triradiate system, 74– 197.4 –267 x 8.5– 12.4 –16 µm, apical actines curved, often wobbly ( Fig. 25e View FIGURE 25 ), 35– 110.3 –237 x 4.5– 10.3 –16 µm.

Ecology. So far known only from a marine lake, at shallow depth on mangrove roots.

Distribution. So far known only from Kakaban.

Etymology. Named after the type locality, the island of Kakaban, one of the famous marine lakes of Indonesia.

Remarks. The new species is assigned to the genus Ascandra on account of the combination of independent central tubes with proliferated ‘blind’ side tubes, and tetractines lining and echinating the inner tube surfaces with their long curved apical actines. We were unable to demonstrate the presence of a folded choanoderm, but assume the prominent apical actines protruding far into the tube lumen to be sufficient circumstantial evidence for membership of Ascandra .We were able to compare the present species with a specimen of the type species of Ascandra , A. falcata Haeckel, 1870 from NE Spain (ZMA Por. 14591). Shape, color and spiculation are different: A. falcata forms more definitely a group of (yellow) tubes and possesses strongly curved diactines in addition to the triactines and tetractines. It is similar to the present new species in being semitransparent and having the tri- and tetractines approximately similar in size - although more robust - and likewise it has the tetractines larger than the triactines.

The Indonesian species originally described by Haeckel (1872) as Ascandra sertularia , subsequently reassigned to Leucosolenia by Dendy & Row (1913), on paper appears somewhat similar in habitus to our new species. However, Haeckel clearly describes large, peculiarly ornamented diactines arranged perpendicular to the surface, which are not present in our material.

The habitus of our new species is quite striking and distinct, but there is a strong resemblance to Ascandra crewsi sp.nov. described below. The difference between the two is found mostly in the rarity or virtual absence of triactines in A. crewsi sp.nov., whereas the two spicule types are in equal proportions in the present species.