Sycandra rappi Morozov, 2024

Morozov, Grigori & Strelkova, Natalia, 2024, On some Calcaronea (Porifera: Calcarea) from the Barents Sea and adjacent Polar Basin, Zootaxa 5529 (3), pp. 532-550 : 535-538

Sycandra rappi Morozov sp. nov.

Etymology: The species is named in honour of Dr Hans Tore Rapp (1972–2020), whose deep revision of the Arctic calcareous sponges made this work possible.

Material examined: Holotype. Barents Sea, PINRO trawl survey 2003, st. 46 (68.9721N, 37.9826E), 167 m, temperature 7 °C, salinity 34.02 psu, 1 specimen, KFU-LH-2/022 .

Paratype. Barents Sea, PINRO trawl survey 2003, st. 47 (69.4883N, 37.9818E), 141 m, temperature 1.98 °C, salinity 34.529 psu, 1 specimen, KFU-LH-2/043 .

Description: Morphology and anatomy. Sponge tubular, slightly compressed laterally, 1.5 to 5 cm height, gradually tapers toward the base, which embraces the substrate (e.g., bivalve shell). Colour dark brown in alcohol. External surface velvety, slightly hispid. Texture soft and delicate. Single naked apical osculum. Aquiferous system syconoid. Choanocyte chambers fused in their entire length. Distal cones are somewhat visible.

Skeleton ( Fig 2 ). In the atrial cavity there is an additional tissue network, supported by bundles of small atrial diactines. This network can branch extensively, often with some foreign particles incorporated.

Atrial skeleton comprises tetractines with their basal actines lying tangentially and the apical actine projecting into the atrial lumen. The apical actine usually supports the bundles of atrial diactines at their base.

Subatrial skeleton composed of triactines arranged in several rows with their paired actines supporting the atrial skeleton, and the unpaired actine pointing towards the distal cones.

Tubar skeleton composed of parasagittal triactines. These spicules are also present at the distal ends of the choanocyte chambers, with unpaired actines forming the base of the distal cones.

Distal cones decorated with long diactines and trichoxeas protruding slightly through the external surface. Large diactines also cross obliquely the choanosome.

There is no well-defined cortex.

Spicules. Atrial diactines sinuous, one tip fusiform and the other lanceolated. Small spines present near the lanceolated tip ( Figs 3B–B 1 ). Size: 121–244–350 × 3–4.5–6.3 µm (n = 30).

Distal cone diactines straight, with sharp tips ( Fig 3C ). Size: 248–430–1265 × 7.5–10.5–15 µm (n = 20), maybe larger, often broken during preparation.

Trichoxeas ( Fig 3D ), 250–350 × 1 µm, often broken.

Subatrial triactines sagittal, with straight basal actines and ~ 180° angle between the paired actines ( Fig 3E ). Size: paired—68–100–141 × 6–7.2–8.7 µm (n = 35); unpaired—92–150–180.8 × 6.7–8.2–10.2 µm (n = 35).

Tubar triactines parasagittal, with slightly bent paired actines and straight unpaired actine ( Fig 3F ). Size: paired—62.6–122–191 × 5–7–9 µm (n = 50); unpaired—113–184–338 × 4.3–8–10 µm (n = 50).

Atrial tetractines sagittal, with straight basal actines ( Figs 3G–G 2 ). The apical actine is slightly sinuous and much thicker than the basal ones. Size: paired—116–156–185 × 6.5–8.3–10 (n = 10) µm; unpaired—207–268–306 × 7–8.3–9.4 (n = 10) µm; apical—180–236–286 × 7.8–11–16 µm (n = 10).

Remarks: The genus Sycandra Haeckel, 1872 is sufficiently sharply distinguished from the other Grantiid sponges by a complex network of tissue tracts in the atrial cavity, supported by bundles of diactines. However, the present placement of genus in the family Grantiidae is arguable, since there is no true cortex in Sycandra . In the examined specimens we found relatively well-defined distal cones decorated with tufts of long diactines. The same feature was mentioned for Greenlandic specimens of Sycandra utriculus ( Schmidt, 1869) by Lundbeck (1909) and it is also quite obvious from description of S. utriculus given by Rapp (2015). Distal cones decorated with long diactines and the absence of a cortex makes S. utriculus very closely related to representatives of the family Syconidae Poléjaeff, 1883 . However, according to a recent molecular phylogenetic study (Alvizu et al. 2018) the latter is polyphyletic. Members of the family Syconidae , Sycetta Haeckel, 1872 and Sycon Risso, 1827 , were distributed amongst several distant clades in the phylogenetic tree built with the C-region of the 28S rRNA. On account of these facts it is not currently possible to relocate the genus Sycandra into the family Syconidae .

Sycandra is a monotypic genus with Sycandra utriculus recorded for the Northern Hemisphere. Sycandra utriculus was originally described as Ute utriculus by Schmidt (1869) from the coasts of Greenland. Recently, Rapp (2015) re-described S. utriculus . In his material, there was a specimen previously identified as Ute utriculus by Schmidt, which led him to conclude that it was likely the type material of S. utriculus ( Rapp 2015) . Thus, the description given by Rapp (2015) can be considered the description of S. utriculus sensu stricto.

According to the size of the spicules, the apical actine of the tetractines is on average only 156 by 6.1 µm in S. utriculus , almost twice as thin (and shorter) as in S. rappi sp. nov. However, dimensions of spicules in calcareous sponges seem to be subjected to considerable intraspecific variation (see description of S. utriculus below). On the other hand, there is an additional kind of spicule in S. utriculus , a small sickle-shaped diactine found in the distal cones, which is absent in the new species.

Our specimens of Sycandra rappi sp. nov. were found on several occasions in the southern Barents Sea, north off the Kola Peninsula. Apparently, S. rappi sp. nov. and S. utriculus are sympatric, with partially overlapping geographical ranges ( Fig 4 ). Thus, careful examination of spicules is required.

Figures

FIGURE 1. Map of sampling locations in the Barents Sea and adjacent areas.

FIGURE 2. Sycandra rappi Morozov sp. nov. Schematic diagram of skeleton organization.Abbreviations: ab = bundle of small atrial diactines, supported by apical actine of the tetractine at the base; as = atrial skeleton; ss = subatrial skeleton; ts = tubar skeleton; dc = skeleton of distal cones.

FIGURE 3. Sycandra rappi Morozov sp. nov. A. Holotype specimen KFU-LH-2/022, habitus. B–B1. Atrial diactines. C. Distal cone diactines. D. Trichoxea. E. Subatrial triactine. F. Tubar triactine. G–G1. Atrial tetractines. G2. Apical actine of the tetractine. Abbreviations: p = paired actine; u = unpaired actine; a = apical actine.

FIGURE 4. Distribution of Sycandra spp. in the North Atlantic and Arctic. Data from Haeckel (1872) is indicated by question marks since he did not specify exact sampling locations.