Sarsinella karasikensis, 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 : 241-245

Sarsinella karasikensis sp. nov.

( Figs 18 A–H, 19A–H, 20A–F; Table 14 )

Diagnosis. Sarsinella with strongly villous surface due to very long protruding diactines and trichoxeas, which are organized in tufts. Well-developed oscular fringe, which is formed by long and straight trichoxeas. Articulated skeleton composed of several rows of tetractines.

Type locality. Arctic Mid Ocean Ridge.

Material examined. Holotype: ZMBN-127212, Arctic Mid Ocean Ridge , G.O. Sars 2016, St. GS16- ROV4 , Protocol 18, 652- 1314 m depth (73°47.28’N, 07°35.11’E) . Paratype: ZMBN-127210, Karasik Seamount, Gakkel Ridge, Polarstern 2016, ps101/200# 3, 684 m depth (86°51.49’ N, 061°35.76’ E) . Paratype: ZMBN-127211, Arctic Mid Ocean Ridge , St no. GS16-BC1, Protocol # 3, 773 m depth (73°48.705’N, 07°30.838’E) . Paratype: ZMBN- 127213, Karasik Seamount, Gakkel Ridge, Polarstern 2016, ps101/200 # 2, 684 m depth, (86° 51.49’ N, 061° 35.76’ E) . Paratype: ZMBN-127214, Karasik Seamount, Gakkel Ridge, Polarstern 2016, ps101/200 # 1, 684 m depth, (86° 51.49’ N, 061° 35.76’ E).

Etymology. Named after the locality Karasik Seamount on the Gakkel Ridge where most of the paratypes were found.

Morphology. Sponge vase-shaped, broadest at mid-height, and with one apical osculum with well-developed fringe. Surface strongly villous due to very long diactines and trichoxeas that are protruding the surface ( Fig 18A ). The size of the sponge is 2–4 cm height, and 0.5–2 cm width. The thickness of the sponge wall is 607.1–1256.2 µm. Colour in life and in ethanol is similar, white-brownish due to sediment trapped on the surface. Aquiferous system syconoid with elongated choanocyte chambers that are completely free, with sizes ranging from 724.3 to 1238.1 µm length and from 133.5 to 227.4 µm width ( Fig 18B ).

Skeleton. Cortical skeleton composed of two types of triactines placed tangentially, and diactines with small spines which are scattered around the inhalant pores ( Fig 18C ). Fairly long diactines and trichoxeas organized in tufts are also part of the cortical skeleton ( Figs 18 D–E). Choanoskeleton articulated with several rows of tetractines ( Fig 18F ). These tubar tetractines are placed with the unpaired actines towards the cortex, paired actines adjacent to the atrial wall, and apical actines straight and projecting into the atrial cavity ( Figs 18 G–H). Atrial skeleton built by two kinds of chiactines, which are placed as the tubar tetractines ( Figs 18F, 18H ). Oscular collar composed of tetractines and triactines, and the oscular fringe is well-developed, and is formed by long and straight trichoxeas ( Fig 19A ).

Spicules. Cortical diactines I: very long diactines with hastate points. Size: 1417.2 ± 509.3 µm length, 18.6 ± 5.1 µm width ( Fig 19B ; Table 14 ). Cortical diactines II: small, straight and spined with sharp tips. This type of diactines are also found in the tufts of diactines II and trichoxeas ( Figs 19 B–C). Size: 169.6 ± 30.1 µm length, 3.7 ± 0.7 µm width ( Table 14 ).

Cortical triactines I: sagittal, alate with unpaired actines shorter than the paired ones ( Figs 18C , 19D ). Size: unpaired actines 101.5 ± 34.3 µm length, 8.9 ± 1.7 µm width; paired actines 154.5 ± 36.2 µm length, 9.0 ± 1.5 µm width ( Table 14 ).

Cortical triactines II: unpaired actines longer than the paired actines, which are slightly bent upwards forming a round bend ( Figs 18C , 19E ). Some of this triactines present paired actines with different length ( Fig 19F ). Both types of triactines are scattered unevenly on the cortical skeleton ( Fig 18C ). Size: unpaired actines 266.1 ± 81.7 µm length, 6.1 ± 8.4 µm width; paired actines 178.2 ± 38.6 µm length, 5.7 ± 0.8 µm width ( Table 14 ).

Tubar tetractines: unpaired actines longer than the paired ones. Apical actines very short with conical shape and slightly bent upwards ( Fig 19G ). The tetractines placed closer to the cortex have the paired actines slightly bent upwards forming a round angle, while those tetractines closer to the atrium have an unpaired angle almost straight ( Fig 19G ). Size: unpaired actines 229.8 ± 56.6 µm length, 9.4 ± 0.9 µm width; paired actines 137.3 ± 18.5 µm length, 9.8 ± 1.0 µm width; apical actines 34.5 ± 10.1µm length, 6.4 ± 1.6 µm width ( Table 14 ).

Chiactines: most have straight and longer unpaired actines, and the paired ones are bent forwards and can present different length ( Figs 19H , 20A ). The chiactines found around the apertures of the choanocyte chambers to the exhalant cavities present unpaired actines shorter than the paired actines, and even shorter than the apical actine ( Figs 20 B–C). Apical actines are conical and with hastate tip. Size: unpaired actines 215.1 ± 79.2 µm length, 7.3 ± 1.2 µm width; paired actines 131.8 ± 25.8 µm length, 7.4 ± 1.4 µm width; apical actines 81.6 ± 16.2 µm length, 6.2 ± 1.0 µm width ( Table 14 ).

Trichoxeas: very long and straight which form the well-developed oscular fringe and the tufts of diactines and trichoxeas in the cortical skeleton. Size: 1043.5 ± 396.9 µm length, 3.7 ± 1.8 µm width ( Fig 20D ; Table 14 ).

Oscular chiactines: chiactines with unpaired and paired actines longer than those found in the atrial skeleton. The oscular chiactines together with the oscular triactines support the oscular frame. Size: unpaired actines 481.2 ± 160.0 µm length, 7.8 ± 1.5 µm width; paired actines 171.1 ± 90.8 µm length, 8.3 ± 2.3 µm width; apical actines 86.2 ± 13.9 µm length, 6.6 ± 1.0 µm width ( Fig 20E ; Table 14 ).

Oscular triactines: long and alate triactines. Size: unpaired actines 461.9 ± 123.1 µm length, 6.1 ± 2.0 µm width; paired actines 139.8 ± 34.3 µm length; 7.7 ± 1.6 µm width ( Fig 20F , Table 14 ).

Molecular identification. Sequences of 18S and 28S rRNA genes are available on GenBank with the following accession number: 18S: MH385159 , MH385160 ; 28S: MH385223 , MH385222 ( Alvizu et al. 2018), MK696119 and MK696120.

Remarks. The distinctive characteristics of this new chiactines-bearing species is the presence of a real articulated skeleton composed only of tetractines, and also the absence of the typical minute spined diactines which are present in almost all species within this family. There was no intraspecific variation registered between the sequences of the four specimens examined.

Figures

FIGURE 18A–H. Sarsinella karasikensis sp. nov. A: preserved holotype. B: histological section including cortical layer, choanosome and atrial cavity. C–E: SEM images of the cortical layer. F: histological section of the choanosome. G–H: SEM images of the choanosome. Abbreviations: At = atrial cavity; Chc = choanocyte chambers; Cho = choanosome; Cor = cortical layer/cortex; CtrI = cortical triactines I; CtrII = cortical triactines II; DiI = diactines I; Ino = inhalant openings; Tut = tubar tetractines.

FIGURE 19A–H. Sarsinella karasikensis sp. nov. A: histological section of the oscular region. B–C: SEM images of diactines I and II. D: SEM image of cortical triactines I. E–F: SEM images of cortical triactines II. G: SEM image of tubar tetractines. H: chiactines. Abbreviations: CtrI = cortical triactines I; DiI = diactines I; DiII = diactines II; Tut = tubar tetractines; Osf = oscular frame.

FIGURE 20A–F. Sarsinella karasikensis sp. nov. A: SEM image of atrial chiactine and cortical triactine type II. B: SEM image of a chiactine found around the exhalant opening. C: SEM images of the atrial layer including an exhalant opening. D: SEM image of trichoxea. E: SEM images of oscular chiactine. F: SEM images of oscular triactine. Abbreviations: Chi = chiactines; CtrII = cortical triactines II; Exo = exhalant opening.