Grantia arctica
Creators: name: Morozov, Grigori
name: Strelkova, Natalia
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Porifera
Calcarea
Leucosolenida
Grantiidae
Grantia
Grantia arctica

description: Grantia arctica (Haeckel, 1872)
Synonyms and citations: Sycandra arctica (Haeckel 1872). Sycon protectum (Lambe 1896, 1900). Grantia arctica (Breitfuss 1898; Rapp 2015 and references therein). Sycon arcticum (Burton 1963).
Previous records: Greenland and Spitsbergen (Haeckel 1872), Baffin Bay and Davis Strait (Lambe 1896, 1900), Kola Peninsula (Breitfuss 1898, 1911).
Material examined: Barents Sea, 2003 (68.4245N, 39.3997E), 73 m, temperature 4.48 °C, salinity 34.263 psu, 1 specimen, KFU-LH-2/036. Barents Sea, Murman Coast, 15 Dec. 1987, 1 specimen, ZISP 10188.
Franz Josef Land, Hayes Island, 3 m, 12 Oct. 1982, leg. Pushkin, box corer (0.1 m 2), 1 specimen, ZISP 10187.
Description: Morphology and anatomy. Sponge egg shaped (Fig 6A–B), around 1.5 cm height, broader in the middle, tapering toward the round base. Colour light yellow in alcohol. Single apical osculum surrounded by a very long fringe of diactines (up to 5 mm). The surface is optically smooth, slightly shaggy to the touch. It is perforated with minute pores, openings of the incurrent canals, at right intervals, giving the surface a very characteristic pattern (Fig 6C). Aquiferous system syconoid. Choanocyte chambers fused in their entire length. The distal end of each chamber decorated with tufts of diactines.
Skeleton. Atrial skeleton very thick and comprising sagittal tetractines arranged in several rows, with their basal actines lying tangentially and the apical actine projecting into the atrium.
Tubar skeleton articulate, consisting of triactines arranged around choanocyte chambers, with their unpaired actines oriented toward the cortex (Fig 6D).
Cortical skeleton comprises sagittal triactines, with the unpaired actine bent at a 90 o angle near its base. These spicules are found in groups arranged around the openings of the incurrent canals so that the bent unpaired actines are directed towards the centre of the opening (Fig 6E). Cortical tufts are composed of diactines and the unpaired actine of triactines.
Diactines are not found exclusively in the cortex, but obliquely cross one-third to half of the choanosome.
Trichoxeas and small diactines are found scattered through the surface of cortex.
Spicules from the main body. Cortical diactines, small, with one lanceolated tip and another sharply pointed (Figs 7A–A 1). Size: 165–200.9–252.2 × 2.5–4–4.8 µm (n = 20).
Cortical diactines large, with one tip fusiform and slightly rounded, and the other sharply pointed (Fig 7B). Size: 296–2000 8–20.8 µm (n = 10), often broken.
Cortical trichoxeas (Fig 7C), quite long, up to 700 × 2 µm, maybe longer, often broken.
Subatrial and tubar triactines with stout, conical, sometimes slightly sinuous actines, varying from ‘ T -’ (Fig 7D) to ‘ Y-shaped ’ (Figs 7E, F). Size: paired—64.8–102–134.4 × 9.35–13–16.5 µm (n = 50), unpaired—74–151–248 × 6.5–12–15.5 µm (n = 50).
Cortical triactines sagittal, with straight, sharply pointed paired actines, and unpaired actine often bent at 90 degrees angle near the base (Figs 7G–G 1). Size: 74.9–93–114.3 × 7.8–9.7–11.8 µm (n = 30).
Atrial tetractines sagittal (Fig 7H) with undulating paired actines, often having rounded tips. Unpaired actine straight, short-pointed. Apical actine stocky, cone-shaped. Size: paired—109.3–164–266 × 7–10.9–15.5 µm (n = 30), unpaired—96.6–217–301 × 7.2–11.8–15.5 µm (n = 30), apical—56.8–102–150 × 9.7–14.5–20.1 µm (n = 15).
Spicules from the fringe. Diactines very long, up to 5 mm length and 8.5–15.5 µm thick, with one sharplypointed tip and the other lanceolated. Short spines present near the lanceolated tip (Figs 8D–D 3).
Triactines sagittal of two different kinds. Triactines small with unproportionally large paired actines (Fig 8A), and short, slender unpaired actine. Size: paired—121–278–462 × 3.9–6.5–9.3 µm (n = 20); unpaired 72.8–130–261 × 2–3.7–5.4 µm (n = 20). Triactines large, regular (figs. 8B–C). Size: paired—144–212–339 × 9–11–13.5 µm (n = 10); unpaired—47–188–284 × 8.2–12–14.9 µm (n = 10).
Remarks: Sycon protectum (Lambe, 1896), a species widely distributed in Canadian waters with a “ grantioid condition of the skeleton ” (Burton 1963, p. 414), has been proven to be a junior synonym of the Arctic sponge Grantia arctica (Haeckel, 1872), as recently shown by Rapp (2015), who analysed samples from around Greenland, including a type specimen of S. protectum.
Grantia arctica is an egg-shaped sponge, attached by its broadly rounded base and with a large osculum at the upper end surmounted by a fringe of long diactines. This species has a very rough surface owing to the prominent large spicules of the cortex. This latter feature was repeatedly stressed by other Arctic spongiologists (Fristedt 1887; Levinsen 1887; Lambe 1896, 1900; Breitfuss 1898a) and is clearly seen in the figures provided by Rapp (2015, Fig 31a).
Our specimens bear many characters in common with G. arctica when it comes to spicules and skeletal structure. However, our samples, both from Kola peninsula and Franz Josef Land, differ in overall appearance: dermal diactines are much shorter and do not protrude far beyond the cortex; as a result, the outer surface seems to be smooth (Figs 6A, B). Another clear difference is the presence of two types of cortical diactines in our specimens: long, fusiform diactines with two slightly different tips (388–2000 × 8–20 µm), and small diactines with one lanceolated tip and the other sharply pointed (165–252.2 × 4 µm). In G. arctica, on the contrary, cortical diactines are distinctively larger and of one type only, 1450–3200 × 19 µm (Rapp 2015). However, small lanceolated diactines might have been previously overlooked.
Atrial tetractines in G. arctica s. str. have very short, almost reduced, stout and cone-shaped apical actines, 12–27 × 8.5 µm; paired actines are straight. In our specimens the apical actine is much larger, 56.8–102–150 × 9.7–14.5–20.1 µm and paired actines are slightly, but characteristically undulated.
From Rapp’s description of G. arctica, it is obvious that he did not examine the composition of spicules of the oscular fringe in detail. The long oscular fringe diactines of our specimens bear small spines near the lanceolated tip (Fig. 8D 2 –D 3). These spines are only barely visible under a light microscope and might have been overlooked in G. arctica s. str. Finally, we found additional spicule types in the oscular fringe: triactines with unproportionally long paired actines (Fig 8A) and large sagittal triactines (Fig 8B, C).
The aforementioned differences can hardly confirm that our samples comprise a new species, unless the holotype of G. arctica is analysed.
description: Published as part of Morozov, Grigori & Strelkova, Natalia, 2024, On some Calcaronea (Porifera: Calcarea) from the Barents Sea and adjacent Polar Basin, pp. 532-550 in Zootaxa 5529 (3) on pages 540-544, DOI: 10.11646/zootaxa.5529.3.6, http://zenodo.org/record/14022853