Megapogon schiaparellii, Alvizu & Xavier & Rapp, 2019

Alvizu, Adriana, Xavier, Joana R. & Rapp, Hans Tore, 2019, Description of new chiactine-bearing sponges provides insights into the higher classification of Calcaronea (Porifera: Calcarea), Zootaxa 4615 (2), pp. 201-251 : 229-232

Megapogon schiaparellii sp. nov.

( Figs 12 A–F, 13A–D; Table 10 )

Diagnosis. Megapogon with sylleibid aquiferous system. Cortical skeleton is composed of sagittal triactines, trichoxeas and two types of diactines positioned perpendicularly. Spined microdiactines present scattered in the choanoskeleton and atrial skeleton.

Type locality. Tethys Bay , Antarctic .

Synonym and citations. M. raripilus, Alvizu et al. 2018, p. 282 ; M. raripilus, Ghiglione et al. 2018, p. 149 .

Material examined. Holotype: MNA-08193 (complete specimen), PNRA XVII Exp 01/02, Grab 18, 11.01.2002, Northwest Basin, 530 m depth (72°51’41.4”S 171°05’13.8”E), Leg. Remia Alessandro & Oliverio Marco . Paratype: MNA-07813 (complete specimen), PNRA XXVIII Expedition 12/13, Dredge 6, collection date 15.01.2013, Caletta, 146 m depth (74°45’43.5”S 64°05’46.4”E), Leg. Stefano Schiaparelli . Paratype: MNA-02762 (complete specimen), PNRA XXV Expedition 09/10, Dive 5, collection date 13.12.2009. Tethys Bay “zecca”, 23 m depth (74°41’25.0”S 164°06’09.2”E), Leg. Stefano Schiaparelli .

Etymology. Named after the Dr. Stefano Schiaparelli from Italian National Antarctic Museum, in Genoa Italy, who organized the collection of the material.

Morphology. Cylindrical sponge, with an apical osculum without a well-developed fringe. Surface minutely hispid due to projecting diactines and trichoxeas ( Fig 12A ). Aquiferous system sylleibid formed by choanocyte chambers more or less rounded ( Fig 12B ). The holotype size (MNA-08193) is 17.5 mm long and 9 mm wide. The paratypes size are 25.3 mm long and 5.3 mm wide (MNA-02762) and 13.1 mm long and 3.3 mm wide (MNA- 07813) is 13.1 mm long and 3.3 mm wide.

Skeleton. Cortical skeleton composed of sagittal tangential triactines, trichoxeas and two types of diactines positioned perpendicularly ( Figs 12 C–D). The trichoxeas are arranged in bundles which penetrate the choanosome but do not reach the atrium ( Fig 12D ). The choanoskeleton is inarticulated. Small and spined microdiactines are found around the choanocyte chambers and scattered in the atrial skeleton ( Figs 12 E–F). The atrial skeleton is mainly supported by the paired actines of chiactines with the unpaired actines pointing towards the cortex, and the apical actines crossing through the atrial wall into the atrium. Sagittal triactines are irregularly scattered in the atrial skeleton ( Fig 12D ). The oscular margin is composed of the same cortical diactines I and long trichoxeas.

Spicules. Diactines I: large projecting, curved towards the distal end and with blunt tip. The proximal end is thinner and sharply pointed ( Fig 13A ). Size: 494 ± 101.2 µm length, 16.4 ± 4.2 µm width ( Table 10 ).

Diactines II: cortical diactines smaller that diactines I, and slightly spined. The ring on the “set-over” can be less pronounced ( Fig 13B ). This type of diactines is also found in the trichoxeas bundles that cross the choanosome. Size: 151.1 ± 15.1 µm length, 5.6 ± 0.8 µm width ( Table 10 ).

Microdiactines: minute, slightly bent, strongly spined and sharply pointed ( Fig 12F ). Size: 71.1 ± 8.7 µm length, 3.9 ± 0.9 µm width ( Table 10 ).

Trichoxeas: long and straight ( Fig 12D ). Size: 742.4 ± 74.2 µm length, 3.8 ± 0.6 µm width ( Table 10 ). Cortical triactines: sagittal with unpaired actines longer than the paired ones. The paired actines are bent up- wards making the unpaired angle rounded ( Fig 13C ). Size: unpaired actines 205.7 ± 42.6 µm length, 10.5 ± 1.9 µm width; paired actines 157.6 ± 21.7 µm length, 10.1 ± 2.4 µm width ( Table 10 ).

Atrial triactines: “T” shaped with unpaired actines longer than the paired ones. Some atrial triactines have the unpaired angle rounded similar to cortical triactines ( Fig 13D ). Size: unpaired actines 335 ± 84.8 µm length, 10.8 ± 1.3 µm width; paired actines 187.6 ± 28.6 µm length, 10 ± 1.6 µm width ( Table 10 ).

Chiactines: longer and straight unpaired actines and the paired actines can be straight with the unpaired angle around 180º ( Fig. 13C ), or slightly bent forming a rounded bend ( Fig 13D ). Both types can be found in the atrial skeleton and in the oscular region. Size: unpaired actines 411.3 ± 135.6 µm length, 12 ± 1.7 µm width; paired actines 195.7 ± 48.3 µm length, 11.9 ± 1.6 µm width; apical actines 78.3 ± 17 µm length, 10.2 ± 1.9 µm width ( Table 10 ).

Oscular tetractines: not measured because they were difficult to find in the spicule preparations and in the sections.

Distribution and depth. This new species of Megapogon has been reported in different localities around the Antarctic, including the ecoregions Ross Sea and East Antarctic Wilkes Land. Megapogon schiaparellii sp. nov. also presents a wide depth distribution, from 18 m to 530 m.

Molecular identification. The 28S sequences available in GenBank with the accession numbers MH385273 , MH385274 and MH385275 , that previously were assigned to M. raripilus ( Alvizu et al. 2018) are now reallocated to the new species M. schiaparellii . An additional sequence of 18S rRNA for M. schiaparellii sp. nov. was added in GenBank under the accession number MK696125 .

Remarks. After re-examination of the type material of M. raripilus we found consistent morphological differences between this species and the specimens identified as M. raripilus in previous studies (Ghiglione et al. 2018, Alvizu et al. 2018). The most remarkable difference is the sylleibid aquiferous system found in M. schiaparellii sp. nov., while in M. raripilus it is leuconoid. The spiculation is also dissimilar, for example the new species presents a type of diactines (type II) that is absent in M. raripilus . Based on these morphological characteristics the two species can be easily separated. Therefore, the specimens identified as M. raripilus in Alvizu et al. (2018) and Ghiglione et al. (2018) are reallocated to the new species M. schiaparellii .

Figures

FIGURE 12A–F: Megapogon schiaparellii sp. nov. A: preserved holotype MNA-02762. B: histological section including cortical layer, choanosome and atrial cavity. C: SEM image of cortical layer. D: histological section including cortical layer, choanosome and atrial cavity. E: histological section showing choanocyte chambers. F: SEM image of microdiactine. Abbreviations: At = atrial cavity; Chc = choanocyte chambers; Cor = cortical layer/cortex; Ctr = cortical triactines; Di = diactines; Mic = microdiactines; Tric = trichoxeas.

FIGURE 13A–D. SEM images of spicules of Megapogon schiaparellii sp. nov. A: diactine I. B: diactine II. C–D: cortical triactines, atrial triactines and chiactines. Abbreviations: Atr = atrial triactines; Chi = chiactines; Ctr = cortical triactines.