Niquivilispongia asteria, Carrera & Botting & Cañas, 2025

Carrera, Marcelo G., Botting, Joseph P. & Cañas, Fernando L., 2025, Heteractinid, hexactinellid and sphaeroclonid sponges as rare components of anthaspidellid-dominated reefs from the Ordovician of the Precordillera, western Argentina, Palaeontologia Electronica (a 17) 28 (1), pp. 1-17 : 5-8

publication ID	https://doi.org/10.26879/1351
publication LSID	lsid:zoobank.org:pub:2E6F520E-FAEB-40F3-A313-681254BE1BB2
persistent identifier	https://treatment.plazi.org/id/3E1DC918-FFF2-810D-7AF7-F9CBFC5BBB3F
treatment provided by	Felipe
scientific name	Niquivilispongia asteria
status	sp. nov.

Treatment

Niquivilispongia asteria sp. nov.

Figures 3-4 View FIGURE 3 View FIGURE 4

zoobank.org/ 3E1D53E0-0F1D-4D04-A84C-6FE47D989146

Diagnosis. Domal to mound-shaped, encrusting heteractinid sponge with homogeneous, dense spicular net, mainly composed of hexaradiate heteractins (six rays in one plane) and small monaxons. A complex root tuft of irregular undulating monaxon-like spicules and hypertrophied heteractinid rays emerge from the base of the sponge body.

Etymology. From Greek, asteria , meaning stars, referring to the star-like appearance of the heteractinid spicules.

Holotype. CEGH-UNC 27593 , a section through the sponge in a thin section.

Paratypes. CEGH-UNC 27594-27595 ; additional thin sections cutting through sponges, from the type locality .

Type locality. Niquivil, Precordillera of Argentina; Middle Ordovician (early Dapingian; T laevis - B navis Conodont zones, Monorthis cumillangoensis Brachiopod Zone ).

Description. Domal to mound-shaped encrusting heteractinid sponge 4 to 5 cm in maximum diameter (measured at the base). No evidence of central cavity or canals are seen within the homogeneous, dense spicular net, which is mainly composed of hexaradiate heteractins (six rays in one plane) and small monaxons.

The heteractine spicules are 1 to 1.5 mm in maximum diameter, and typically 60–80 μm in basal ray diameter. No size ranks are observed, although traces of numerous finer spicules are visible in the background. The heteractins are octactine where visible, with six horizontal (in one plane) slightly curved rays and two perpendicular rays, arising from the axis. All rays equal in size and thickness.

At a first glance the thin sections appear to show a small number of hexactin-type spicules, with four equal rays in one plane, of the same size as the heteractine spicules, and with similar morphology of evenly tapered, sometimes curved rays. Rays in one plane are generally orthogonal, but some show deviations, including possibly interposed rays bisecting the space between two others ( Figure 3G View FIGURE 3 ). However, this is almost certainly an artefact of the angle of section through standard octactins (see remarks).

Internal structure of the spicules is generally replaced by coarse calcite cement showing typical drusy texture with increasing crystallite size towards the center. Some spicules show an axial hollow, either irregular (typical of incomplete infill of cavity following spicule dissolution) or with a sharp, circular boundary. In the latter case, the hollow is approximately 100 μm in diameter. In some of the entirely calcitized spicules, there is a circular, axial discontinuity within the structure, of similar dimensions ( Figure 4 View FIGURE 4 J-K).

A complex root tuft or similar structure emerges from the base of the sponge body in one paratype, the spicules protruding from the base of the sponge either as a continuation or extension of the main spicule rays, or as simple juxtaposed monaxon-like spicules ( Figure 3 View FIGURE 3 I-K; Figure 4C View FIGURE 4 ). Some of the spicules included in this skeletal base appear to be fine-rayed heteractins or similar, with shortened lateral rays and extended, undulating basal rays.

Remarks. The possible presence of hexactins is a critical feature for the interpretation of the affinities of the new sponge ( Botting and Butterfield, 2005) and needs to be considered carefully. Such features can be especially challenging in thin sections; thin-walled heteractinids like Eiffelia are preserved on rock surfaces, where orientations are consistent, and spicule morphology is easier to assess. For thick-walled heteractinids, there is much more scope for variability in orientation, leading to misleading appearance due to the angle of section. Unfortunately, the small size and the lack of mineralogical contrast of the spicules versus the host rock prevent the use of MicroCT to generate a three-dimensional view. To address this, we considered all possible sectioning planes through an octactine spicule, as some orientations can show the presence of four rays in a plane (appearing as a hexactin or derivative), and we compared this with the observed frequency of such spicules. If the spicules were all octactins, then there is only one orientation of section that would give six visible rays, but three (along each of the coplanar axes) that would make them appear as triaxons (i.e., hexactins/stauractins). Therefore, with random orientation of spicules, we would need to see significantly more than three times as many ‘hexactins’ as hexaradiate spicules, in order to assume that genuine triaxons were present. Instead, we found that the proportion of apparent hexactins is very low, with at least 20 hexaradiate views for each four-rayed view within a given field of view. This is much lower than expected for a random orientation of octactins and indicates a preferred orientation with the six coplanar rays approximately parallel to the angle of section (which appears to be parallel to the body wall). Overall, it is most likely that the apparent four-rayed spicules are in fact octactins cut through one of three possible planes.

Differentiation from other genera of the family was discussed under the genus heading. Distinction between species of the genus, if more are discovered, should be based on minor skeletal features, such as spicule net arrangement, types and proportions of spicules, or their size and arrangement. Development of canals could also be taken into account for species differentiation, together with any consistent difference in body form.

References

Figures

FIGURE 3. Niquivilispongia asteria gen. et sp. nov. A. General view of an almost complete specimen (thin section CEGH-UNC 27595) showing a laminar to encrusting morphology of the sponge interrupted by vertical dissolution gaps, scale bar equals 1 cm. B. General view of the specimen in thin section (Holotype CEGH-UNC 27593), showing a mound shaped sponge form at the top and a laminar to encrusting form at the base, scale bar equals 1 cm. C. Closeup of 3B showing the mound shaped form at the top, irregular arrangement of heteractinid spicules and below the base the microproblematicum Allonema, scale bar equals 5 mm. D. Detailed view of figure 3A showing a partially dissolved sponge structure with isolated hexaradiate heteractinid spicules, scale bar equals 5 mm. E. Close-up of figure 3C with hexaradiate heteractinids and views of heteractinids showing slightly curved rays, scale bar equals 1 mm. F. Detailed view of the previous thin section figure 3E, showing heteractinids with the view of four curved rays, scale bar equals 1 mm. G. Close-up of figure 3E showing heteractinids in different views with six rays in a plane and four curved rays in a plane. Arrows show two divergent ray bases in the center of an apparent “four rayed hexactin”, and interposed rays bisecting the space between two others, scale bar equals 1 mm. H. Transversal view of at the base of the sponge (CEGH-UNC 27594) showing modified undulate monaxon-like spicules or modified rays of heteractinid-based spicules, scale bar equals 1 mm. I. Transversal view of the same thin section showing the transition of the main sponge spicules and the modified spicules (hypertrophied heteractinid rays and possible monaxons) of the root tuft structure, scale bar equals 1 mm. J. The same transversal view showing an adjacent extended part of the root tuft structure and the transition of the main sponge spicules, scale bar equals 1 mm.

FIGURE 4. Niquivilispongia asteria gen. et sp. nov. A. Detailed view of a thin section (Holotype CEGH-UNC 27593) with heteractinid spicules with filled or hollow axial regions preserved as calcareous blocky or drusy cement, scale bar equals 0.5 mm (500 µm). B. Another view of the same thin section mainly showing hexaradiate heteractinids, scale bar equals 0.5 mm (500 µm). C. Detailed view of the long undulate rods of monaxons or expanded hypertrophied spicule rays of the root tuft structure (CEGH-UNC 27594) scale bar equals 0.2 mm (200 µm). D. Close-up of heteractinid spicules (Holotype CEGH-UNC 27593), including “four rayed” visual sections, with spar filled cement and a blocky differential cement in the center or a hollow core in others, scale bar equals 0.5 mm (500 µm). E. Detailed view of a four rayed heteractin with a core filling by a differential blocky spar cement, scale bar equals 0.2 mm (200 µm). F. Detailed view of an heteractinid showing orthogonal rays to the six rays in a plane, and a view of a partial section of an heteractinid with interposed ray bisecting the space between two others, scale bar equals 0.2 mm (200 µm). G. Close-up of an heteractinid with apparently six rays in one plane and a vertical ray, scale bar 0.2 mm (200 µm). H. A close-up of a curve rayed heteractinid with a big crystal spar cement in the axial core, scale bar equals 0.2 mm (200 µm). I. Four rayed view of a heteractinid with spar axial infilling, scale bar equals 0.2 mm (200 µm). J. A detailed view of figure 5D showing a hollow core, scale bar equals 0.2 mm (200 µm). K. A detailed view of figure 4A showing another hollow core in the axial infilling, scale bar equals 0.2 mm (200 µm).