Rappya australiensis, Klautau & Lopes & Tavares & Rizzieri & Sorokin & Fromont & Goudie & Crowther & McCormack & George & Wahab, 2025

Rappya australiensis View in CoL gen. nov., sp. nov.

( Figs 23, 24; Table 12)

Zoobank registration: urn:lsid:zoobank.org:act:

Etymology: Named for the type locality, Australia.

Diagnosis: Sponge tubular. Cortex delicate, composed of large tangential triactines. Choanosomal skeleton articulated but disorganized, composed of small triactines and tetractines. Atrial skeleton thin, composed of triactines and interrupted by large exhalant canals. All the spicules have cylindrical actines with rounded to blunt tips.

Type material: Holotype, SAMA S1891, GAB, 34°17 ʹ 30″S, 132°42 ʹ 24″E, 283 m depth, coll. GABRP, site IN2015 _C02_181, 7 December 2015. GoogleMaps

Colour: White in ethanol ( Fig. 23A).

Morphology and anatomy: Sponge solid, tubular, tapering to the base but not forming a peduncle. Cortex smooth. Te osculum is single and apical, without a crown ( Fig. 23A). Te wall is 0.1 cm thick. Te atrium is 0.5 cm in diameter; it has endopinacoderm and is smooth. Te canals in the atrium are spherical, small, and irregularly distributed. Aquiferous system kladonoid, with elongated and copiously branched choanocyte chambers ( Fig. 23B).

Te cortical skeleton is very thin, composed of only one or two layers of tangential large triactines ( Fig. 23C). Te choanoskeleton is articulate but not organized, composed of small triactines and tetractines irregularly distributed ( Fig. 23B, D). Te tetractines project their apical actine into the choanocyte chambers ( Fig. 23E). Te atrial skeleton is composed of tangentially disposed triactines. Te atrial skeleton is not easily recognized because it is very thin (formed by a single layer of triactines) and interrupted by exhalant canals surrounded by the choanosomal triactines and tetractines ( Fig. 23F).

Spicules ( Table 12)

Cortical triactines: Regular (equiangular and equiradiate). Actines are cylindrical, with rounded tips ( Fig. 24A). Size: 167.2 (±24.1)/11.9 (±2.0) µm.

Choanosomal triactines: Regular (equiangular and equiradiate), subregular, or sagital. Te actines are cylindrical, with rounded tips, although sometimes the tips are blunt ( Fig. 24B). Size: 102.6 (±6.6)/5.8 (±0.6) µm.

Choanosomal tetractines: Regular (equiangular and equiradiate), subregular, or sagital. Te basal actines are cylindrical, with rounded tips, although sometimes the tips are blunt ( Fig. 24C). Te apical actine is very thin and cylindrical (needle-shaped), straight or curved, sometimes undulated. It is smooth and has sharp tips ( Fig. 24D). Size: basal, 107.6 (±8.3)/5.7 (±0.6) µm; apical, 67.6 (±13.3)/2.7 (±0.0) µm.

Atrial triactines: Regular (equiangular and equiradiate). Actines are cylindrical, with rounded tips ( Fig. 24E). Size: 124.7 (±14.3)/8.1 (±1.4) µm.

Geographical distribution: Currently known only from the type locality in the GAB.

Ecology: Tis species was found at a depth of 283 m on the edge of the continental shelf (in fine sand and silt).

Taxonomic remarks: According to the molecular tree, this new genus is sister to Lelapiella . It has a general simple tubular structure with a relatively broad atrial cavity; the choanosome contains long, somewhat irregular and occasionally branched tubes, and a distinct well-structured atrial wall is absent. Te specimen has similarities with some genera of Calcarea but could not be allocated to any of them.

Te overall structure of the specimen is similar to Grantia (subclass Calcaronea), a genus that has ‘long and regular radial tubes, which may be branched distally, and a relatively thin atrial and cortical skeletons’ (Borojević et al. 2002). Most Grantia species are single tubes, and several have rare regular or subregular spicules, mostly in the cortical skeleton. However, this specimen has typical equiangular and equiradiate tri- and tetractines, and the nuclei of the choanocytes are always basal, indicating clearly that they belong to Calcinea.

Within Calcinea View in CoL , the genera that could potentially include this specimen are Rowella View in CoL , Leucaltis Haeckel, 1872 View in CoL , and Leucomalthe Haeckel, 1872. Te main differences are the presence of a thick cortex in Rowella View in CoL , and a choanosome with only a few pygmy spicules. Te specimen in this study has a very thin cortex, and the spicules of the choanosome, although smaller than those of the cortex, are not pygmy spicules and are abundant in the walls of the choanocyte tubes.

To date, Leucaltis View in CoL was the only genus with a kladonoid aquiferous system; however, given that the aquiferous system can be highly variable within genera and families, it is not a good character to diagnose these taxonomic ranks. Te species Leucaltis tenuis (Hôzawa, 1939) View in CoL is similar in anatomy and in skeletal architecture and composition to the specimen we examined. In Leucaltis tenuis View in CoL , the atrial skeleton is well developed, with spicules larger than those of the choanosome, as in Rappya australiensis View in CoL . However, Leucaltis spp. are anastomosed, whereas Rappya australiensis View in CoL is a massive sponge. Moreover, the choanosomal spicules in Leucaltis View in CoL are tiny ( sensu Lopes and Klautau 2023), much smaller in size than those of this specimen. In the phylogenetic reconstructions, they are not closely related genera.

Leucomalthe shows some similarities to Rappya australiensis . Leucomalthe was described originally as a subgenus of Leucandra by Haeckel (1872) for the species Leucandra (Leucomalthe) bomba Haeckel, 1872 . Dendy and Row (1913) revised the Calcarea and elevated this subgenus to genus, classifying it in the family Leucascidae because of its aquiferous system with choanocyte chambers ‘radiating from a central gastral cavity’, which they considered similar to that of Leucascus , although they were not certain about the decision. In 1990 and 2002, Borojević and collaborators retained Leucomalthe in the order Clathrinida as incertae sedis ( Borojević et al. 1990, 2002) Although they speculated that this genus could have ‘originated from a Dendya -like sponge through progressive corticalisation and formation of an atrium’, they questioned the allocation of Leucomalthe in the subclass Calcinea, mentioning that the presence of sagital spicules in the atrial skeleton of Leucandra (Leucomalthe) bomba was not characteristic of that subclass. Analysis of the description and drawings made by Haeckel (1872) indicates that the aquiferous system of Leucomalthe is different from that of the specimen in this study. Leucomalthe has radially arranged tubular chambers, decreasing in size hierarchically from the centre to the periphery, different from those observed here.

Considering these data, the specimen could not be allocated to any known genera, and a new genus is established to accommodate it.