Leuclathrina translucida, Voigt & Ruthensteiner & Leiva & Fradusco & Wörheide, 2018

Voigt, Oliver, Ruthensteiner, Bernhard, Leiva, Laura, Fradusco, Benedetta & Wörheide, Gert, 2018, A new species of the calcareous sponge genus Leuclathrina (Calcarea: Calcinea: Clathrinida) from the Maldives, Zootaxa 4382 (1), pp. 147-158 : 151-155

Leuclathrina translucida sp. nov.

( Figs. 2 A–I , 3 A–F ; Table 2)

Diagnosis. Leuclathrina with a yellow cormus composed of two distinct parts: an inhalant body part with macroscopically visible inhalant openings, and an exhalant body part, consisting of several transparent tubes, which emerge from the inhalant body part and occasionally reunite. The skeleton consists of equiradiate triactines lying tangentially in the sponge wall and forming a thick-layered skeleton in the inhalant body parts, and a much thinner layer in the wall of the exhalant tubes. The choanosome is free of spicules and restricted to the inhalant body part.

Type material. Holotype: SNSB-BSPG GW3934 (1 specimen), outer reef wall close to Vavvaru, Lhaviyani Atoll, Maldives (5.4203° N; 73.3508° E), coll. O. Voigt at 23 m on 9 Sept 2015; Paratypes: SNSB-BSPG GW4029 (1 specimen), outer reef wall close to Magoodhoo, Fafuu Atoll, Maldives (dive site 3.0748° N; 72.9663° E), coll. G. Wörheide at 20 m on 12 Oct 2016; SNSB-BSPG GW30279 (4 specimens) & SNSB-BSPG GW30280 (1 specimen), reef wall close to Magoodhoo, Fafuu Atoll, Maldives (dive site Wallino, 3.0870° N, 72.9558° E) coll. O. Voigt & B. Fradusco at 15 –17 m on 29 Sep 2017; SNSB-BSPG GW3 0 292 (1 specimen), inner reef close to Magoodhoo, Fafuu Atoll, Maldives (dive site Coral Garden, 3.09170° N, 72.96787° E), coll. O. Voigt & B.

Fradusco at 20 m on 29 Sep 2017 ; SNSB-BSPG GW30328 (1 specimen), outer reef, Fafuu Atoll , Maldives (dive site Beyrufushi, 3.11282° N, 73.02108° E), coll. O. Voigt & B. Fradusco at 17 m on 1 Oct 2017 ; SNSB-BSPG GW30350 (5 specimens), reef at Bileiydhoo , Fafuu Atoll, Maldives (dive site Wall Street, 3.12061° N, 72.97958° E), coll. O. Voigt & B. Fradusco at 17 m on 2 Oct 2017 ; SNSB-BSPG GW30361 (1 specimen), reef between Magoodhoo and Bileiydhoo , Fafuu Atoll, Maldives (dive site M& Ms, 3.12429° N, 72.99201° E), coll. O. Voigt & B. Fradusco at 15 m on 2 Oct 2017 ; SNSB-BSPG GW30377 (3 specimens), reef wall close to Magoodhoo , Fafuu Atoll, Maldives (dive site Wallino, 3.0870° N, 72.9558° E) coll. O. Voigt, B. Fradusco & G. Wörheide at 20 m on 4 Oct 2017 ; SNSB-BSPG GW30419 (2 specimens), outer reef, E of Magoodhoo , Fafuu Atoll, Maldives (dive site Route 66, 3.07902° N, 72.97797° E), coll. O. Voigt & B. Fradusco at 15 m on 2 Oct 2017 .

Type locality. Vavvaru , Lhaviyani Atoll, Maldives

Etymology. Named for its translucent exhalant tubes.

Colour. Yellow in life ( Figs. 2 A, B ) and in 80 % ethanol.

Growth form. Two different growth forms were observed. The majority of sponges have a cushion-shaped cormus, which is attached to the substrate with its base ( Fig. 2 A ). The holotype measures 3.5 cm x 2.3 cm (fixed as two fragments). Several translucent exhalant tubes (about 2 -2.7 mm wide in the holotype) emerge from the base and sometimes reconnect at their upper parts ( Fig. 2 A ). Only on few occasions, small openings were visible in the exhalant tubes of living specimens, which are most likely oscula ( Fig. 2 A , inset). In fixed material, the oscula are not visible, either because of contraction or due to damage of the delicate exhalant tubes. Two specimens showed a modified growth form and were hanging from ceilings of small or larger overhangs ( Fig. 2 B ). In the larger specimen of this growth form the inhalant body parts were forming a mesh-like structure in some parts of the cormus ( Fig. 2 B ). Exhalant tubes were less developed or contracted in comparison to the more typical growth form ( Fig. 2 B ). In both growth forms, the inhalant body parts have inhalant openings of about 150 to 270 µm in diameter ( Figs. 2 A, C ), which are lacking in the exhalant tubes ( Fig. 2 D ).

Skeleton. The body wall of the inhalant part of the sponge and at the transition between the inhalant and exhalant body parts is supported by a thick layer of tangential triactines ( Figs. 2 E, F ). Towards the more distal parts of the exhalant tubes, the skeleton is getting much thinner ( Fig. 2 G ), consisting of only a thin layer of triactines ( Figs. 2 C, G ). In this region the triactines leave approximately hexagonal shaped areas that are free of spicules, resulting in the transparent appearance of the exhalant tubes ( Fig. 2 D ).

Spicules. Equiangular, equiradiate triactines ( Fig. 2 H ). The actines are straight and conical, with sharp or blunt tips. In some triactines, the actines are locally slightly thickened near the tip ( Fig. 2 H ). Spicule sizes of the holotype are: inhalant region: actine length: 147–194.4–247 µm, actine width: 12–14.4–18 µm; exhalant region: actine length: 143–212.1–256 µm, actine width: 9–14.2–19 µm. Spicules measurements of three paratypes are provided in Table 2.

Histology and organisation of the aquiferous system. The sponge wall of the inhalant body part consists of a thick skeletal layer and the spicule-free choanosome ( Figs. 2 E, I , 3 A ). The skeletal layer is delimited by an exopinacoderm on the outer side and is perforated by inhalant openings, which are lined by endopinacocytes and lead to narrower inhalant canals ( Figs. 2 E , 3 B ). The skeletal layer contains only few mesohyl cells ( Fig. 3 C ). The choanosome layer comprises spherical choanocyte chambers, between which inhalant and exhalant canals occur, which are lined by endopinacocytes ( Fig. 3 D ). The exhalant canals unite and increase their diameter until they open into the central atrium ( Fig. 3 A ). The 3D reconstruction reveals that the diameter of the openings to the atrium increases with the thickness of the choanosome ( Fig. 2 I ). A layer of endopinacocytes delimits the wall of the central atrial cavity ( Fig. 3 E ). Towards the transition of the inhalant to the exhalant tubes the choanoderm decreases its width until it disappears, while the thickness of the skeletal layer remains the same in this region ( Figs. 2 F , 3 I ). The latter however decreases in the more distal parts of the exhalant tubes, until it only contains a thin layer of spicules within a thin mesohyl ( Fig. 2 G , Fig. 3 F ). Oscula were not visible in the fixed material.

Ecology and distribution. The specimens were growing on hard substrate, in most cases on vertical parts of reef walls, on living or dead corals, or hanging from ceilings of small overhangs, in depths between 15 and 23 m. The samples in this study originated from the Maldives; a wider distribution in the Indo-Pacific is mentioned by Coleman (2001), but not further specified.

Remarks. Photographs of Leuclathrina translucida sp. nov. have been published previously, e.g. as ‘ Clathrina sp.’ in the field guide ‘Marine Life of the Maldives’ ( Coleman 2001, page 36).

Leuclathrina translucida sp. nov. differs from the type species of the genus, L. asconoides in several aspects and can easily be distinguished. Leuclathrina asconoides is smaller (3.5 mm) and has a globular shape; its exhalant tubes (‘chimneys’) are shorter (a few millimetres, Borojević & Boury-Esnault 1987). Triactines of L. asconoides can grow to a larger size compared to L. translucida sp. nov.: The length of the actines varies between 156–598 µm, and their width between 13-36 µm ( Borojević & Boury-Esnault 1987).

Figures

FIGURE 3. Histology of L. translucida sp. nov. (SNSB-BSPG 30279), decalcified: A: Section through the sponge wall including the outer skeletal layer, the choanosome and the atrial cavity; B: Detail of an inhalant opening leading to an inhalant canal; C:Detail of theouter skeletal layer, whichis delimitedby exopinacocytes on theexternal surface; onlyfew cells occur in the mesohyl of this layer; D: Detail of the choanosome, with spherical choanocyte chambers and canals of the aquiferous system (inhalant or exhalant), the latter is lined by endopinacocytes. E: Choanoderm adjacent to the atrial cavity. The wall of the atrial cavity is lined by endopinacocytes.F: Section through the wall of an exhalant tube, consisting of an external layerof exopinacocytes and an internal layer of endopinacocytes, and a thin mesohyl layer in between (originally with a few spicules). Abbreviations: at: atrial cavity; c: canal (inhalant or exhalant); ch: choanocyte; chc: choanocyte chamber; enp: endopinacoderm; ex: external side of the sponge; exc: exhalant canal; exp: exopinacoderm; inc: inhalant canal; inh: inhalant opening; mc: mesohyl cell; me= mesohyl; sp: dissolved spicule.

FIGURE2. Leuclathrinatranslucidasp. nov. A:Typicalgrowth form insitu (holotype).The inset shows anopening atthe end of an exhalant tube of another specimen, possibly an osculum; B: Specimen (SNSB-BSPG30280) with a hanging growthform and smaller exhalant tubes. C: Detail of the outer sponge wall of the inhalant region with inhalant openings; C: Detail of the outer sponge wall of the exhalant tubes, showing the hexagonally arranged triactines around the translucent tissue areas (C-D: material fixed in 80 % ethanol); E-G: Section through the sponge wall at different regions of the sponge body; E: In the inhalant region the skeleton consists of several layers of tangential triactines, the choanosome is free of spicules; F: Transition between the inhalant and exhalant region: the choanosome gets thinner and is replaced by a layer of endopinacoderm. G: The thickness of the sponge wall is strongly reduced in the more distal parts of the exhalant tubes. H: Spicules (triactines); I: 3D reconstruction of the skeleton and the choanosome (coloured). Abbreviations: c= canal (inhalant or exhalant); ch= choanosome; enp= endopinacoderm; ex= exterior of the sponge wall; exh= exhalant body part; exp= exopinacoderm; inh= inhalant body part or inhalant opening;sk= skeleton.