Amphoriscus tenax, Pereira & Azevedo & Hajdu & Cavalcanti & Klautau, 2025

Pereira, Sara Emilly, Azevedo, Fernanda, Hajdu, Eduardo, Cavalcanti, Fernanda F. & Klautau, Michelle, 2025, Calcareous sponges (Porifera, Calcarea) from São Sebastião, São Paulo: new species and new records in two marine protected areas of Southeastern Brazil Ecoregion, Zootaxa 5688 (1), pp. 1-107 : 18-26

Amphoriscus tenax sp. nov.

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( Figs. 7–11 ; Table 6)

Etymology: From the Latin tenax , meaning “tenacious” or “adhesive”, referring to the way the tubes tightly adhere to one another when the sponge is manipulated, due to its dense hispidation.

Type locality: Alcatrazes Archipelago , São Sebastião, São Paulo State, Brazil .

Type material: Holotype — MNRJ30124 , Alcatrazes Archipelago , São Sebastião, São Paulo State, Brazil, depth 12 m, coll. M. Custódio & C. Santos, 03/V/2002 . Paratypes —UFRJPOR5976, Paredão do Saco d’água, REBIOMAR Arvoredo, Florianópolis, Santa Catarina State, Brazil ( 27°16'27"S, 48°21'51"W), depth 6–10 m, coll. F. Azevedo & A. Padua, 08/XII/2009 . UFRJPOR6061, Parcel do Boi , REBIOMAR Arvoredo, Florianópolis, Santa Catarina State, Brazil ( 27°17'06"S, 48°22'34"W), depth 10–12 m, coll. F. Azevedo & A. Padua, 11/XII/2009 .

Additional material examined: MNRJ30122 , same as the holotype .

Diagnosis: Amphoriscus with a body composed of ramified tubes, densely hispid due to the presence of two categories of diactines (diactine I, thick and smooth, and diactine II, much thinner and with jagged distal tip). Tufts of anchor-like triactines are distributed throughout the body and concentrated at the base, forming root tufts.

Colour: Beige or white in life and in ethanol ( Fig. 7 ).

Morphology and anatomy: Sponge formed by single or multiple erect tubes, branched at the base ( Fig. 7A–C ). Each tube ends in a single apical osculum with a crown of trichoxeas. The consistency is friable. Numerous diactines and tufts of anchor triactines protrude through the body surface ( Fig. 7A–E ), causing the tubes to easily adhere to one another when the sponge is manipulated, making them difficult to separate (a velcro-like effect). The atrial cavity is also hispid because of the projecting apical actines of the tetractines, in addition to diactines and anchor triactines, which eventually cross the choanosome, piercing the atrium. Aquiferous system syconoid.

The oscular crown is formed by trichoxeas and some diactines, and it is sustained by tetractines and rare triactines ( Fig. 8A ). The cortical skeleton is composed of two categories of diactines and tufts of anchor triactines perpendicularly positioned to the surface, in addition to tetractines and rare triactines ( Figs. 8B ; 9A–F ). The diactines I are more abundant than the diactines II. The choanosomal skeleton is inarticulate, composed of the apical actines of the cortical tetractines and of the unpaired actine of the subatrial triactines and rare tetractines ( Fig. 8C–E ). The atrial skeleton is formed by tetractines and rare triactines ( Fig. 8F ). The anchor triactines are organised in tufts protruding through the surface of the tubes (arrows in Fig. 7B ), but the longest tufts group at the base and are conspicuous in most specimens, where they form “root-tufts”, i.e., structures for attachment to the substrate (arrowheads in Fig. 7B, E ; Figs. 9G, H ; 10 ).

Spicules ( Table 6):

Diactines I: Curved, with the distal tip blunt or sharp and thicker than the proximal tip, which is sharp ( Fig. 11A ). Size: 512.5 (±89.4)/12.5 (±1.8) µm.

Diactines II: Straight through most of their length, but strongly curved at the distal tip, which is jagged and sharply pointed. The proximal tip is smooth and sharp. They are much thinner than diactines I, rare and usually broken ( Fig. 11B ). Size: 407.5 (±42.3)/6.9 (±1.2) µm.

Cortical triactines: Sagittal, variable in shape and size. Some are robust, with conical, stout and sharp actines, similar to the basal system of the cortical tetractines. Others are a little smaller and thinner, with slightly conical and sharp actines. The unpaired actine is straight and usually longer than the paired ones ( Fig. 11C ). Size: paired—143.6 (±27.5)/13.3 (±3.9) µm; unpaired—186.8 (±36.2)/14.5 (±4.7) µm.

Cortical tetractines: Sagittal (near the oscular region, they are even more sagittal). Basal actines are conical, sharp and can be slightly undulated. The paired actines are often curved and a little shorter than the unpaired one ( Fig. 11D ). The apical actine is straight, smooth, conical, sharp and longer than the basal ones, sometimes reaching the atrium. Size: paired—167.0 (±21.5)/18.4 (±2.7) µm; unpaired—172.3 (±25.6)/20.9 (±3.3) µm; apical—196.5 (±23.5)/20.5 (±2.1) µm.

Subatrial triactines and tetractines: Sagittal. Basal actines are slightly conical, with sharp tips. The unpaired actine is straight and longer than the paired ones, which are inwardly curved. In many of them, the paired actines differ in size ( Fig. 11E ). The apical actine is very short, thin, smooth, straight, conical and sharp. Triactines size: paired—122.0 (±9.9)/7.9 (±0.7) µm; unpaired—187.5 (±27.8)/9.6 (±0.7) µm. Tetractines size: paired—114.4 (±15.9)/8.0 (±1.1) µm; unpaired—160.6 (±34.0)/8.6 (±1.6) µm; apical—21.3 (±4.1)/5.2 (±0.5) µm.

Atrial triactines and tetractines: Sagittal (near the osculum, they are strongly sagittal). Basal actines are conical to slightly conical, with sharp tips and may be undulated. The unpaired actine is straight and it can be longer or shorter than the curved paired actines ( Fig. 11F, G ). The apical actine is curved, smooth, conical, sharp and shorter than the basal ones. Triactines size: paired—125.4 (±17.0)/8.2 (±1.0) µm; unpaired—132.7 (±29.3)/8.9 (±1.2) µm. Tetractines size: paired—135.8 (±23.3)/8.3 (±0.9) µm; unpaired—141.3 (±31.2)/9.3 (±0.9) µm; apical— 54.9 (±10.0)/8.3 (±0.9) µm.

Anchor triactines: Anchor-like, variable in size. The unpaired actine is long, curved at the proximal region, cylindrical and sharp, while the paired actines are extremely short and hook-shaped ( Fig. 11H, I ). Size: paired—17.4 (±3.2)/8.7 (±1.3) µm; unpaired—280.9 (±160.3)/10.3 (±1.2) µm.

Ecology: The specimens from São Sebastião were collected alongside Arturia alcatraziensis ( Lanna et al., 2007) , coral polyps, numerous polychaetes, bivalve molluscs, microcrustaceans, and a dromiid crab. The specimens from Arvoredo were collected on a vertical wall, exposed to sunlight, growing anchored through their root-tufts to coralline and green algae ( Fig. 7C, E ), with sediment accumulated among their tubes.

Geographic distribution: Southeastern Brazil ecoregion—Alcatrazes Archipelago (São Sebastião), São Paulo State (present study); Arvoredo Islands, Santa Catarina State (present study), Brazil.

Remarks: Among the 17 valid species of Amphoriscus ( De Voogd et al. 2025) , only two species have anchorshaped spicules: A. synapta (Schmidt in Haeckel, 1872), whose type locality is Bahia, in northeastern Brazil, and A. ancora Van Soest, 2017 , described from the coast of Suriname. Differently from A. tenax sp. nov., A. synapta lacks diactines and has only tetractines in the cortical, subatrial and atrial skeletons. Furthermore, in A. synapta the anchor spicules are tetractines, present only at the base of the sponge, whereas in A. tenax sp. nov. these spicules are triactines and are not restricted to the base of the sponge.

The species that most resembles A. tenax sp. nov. is A. ancora , as they share the presence of anchor triactines. Yet they do not share the same skeletal composition, as A. ancora lacks diactines, cortical triactines, subatrial tetractines, and atrial triactines, spicule categories present in the new species. Additionally, like A. synapta , A. ancora differs from the new species by having tufts of anchor spicules restricted to the base of the sponge.

Klautau et al. (2017) and Cóndor-Luján et al. (2019) investigated attachment structures in the family Amphoriscidae , exploring their potential phylogenetic signal and adaptations to different habitats. Our molecular results suggest that different kinds of attachment structures (peduncle vs root tufts) evolved independently in Amphoriscidae . For instance, three species with peduncle [ A. pedunculatus , Leucilla micropilosa Cóndor-Luján et al., 2018 and Leucilla nuttingi ( Urban, 1902) ] were recovered in a strongly supported clade ( Fig. 2 ; BS = 96%), whereas A. tenax sp. nov. was not part of this group. Interestingly, this clade also includes a species lacking a peduncle, Leucilla mancoraensis . This absence has been suggested to result from secondary loss ( Cóndor-Luján et al. 2019). Amphoriscus tenax sp. nov. was retrieved as a sister species of Sycon caminatum , which lacks attachment structures altogether, with relatively low support. We hypothesise that A. tenax might share closer evolutionary relantioships with A. ancora and A. synapta , but no DNA sequences are currently available for these species to test this hypothesis. Regarding habitat, our observations that A. tenax sp. nov. attaches to other organisms (e.g. algae), usually covered by sediment, via root-tufts agree with Klautau et al. (2017). In fact, it seems that both peduncles and root-tufts may serve for attachment to a variety of organisms, including coralline algae, hydroids, bryozoans, and other sponges ( Klautau et al. 2017).

Figures

FIGURE 2. Maximum likelihood phylogenetic tree based on C-LSU sequences of the subclass Calcaronea. Tree rooted with Leucosolenia complicata. Species sequences generated in this work are in bold, and the clades containing them are highlighted in different colours. Support values (Bootstrap> 70%) are shown at the nodes. H = Holotype, P = Paratype, SP = São Paulo State, SC = Santa Catarina State, ES = Espírito Santo State.

FIGURE 7. Amphoriscus tenax sp. nov. A, B. Preserved MNRJ30124 (Holotype) and fragment of UFRJPOR5976 (Paratype). C. Specimen UFRJPOR5976 in vivo (Photo: V. Padula). D. Detail of the specimen UFRJPOR5976. E. Specimen UFRJPOR6061. Arrows point to tufts of anchor triactines along the body, while arrowheads point to root-tufts of anchor triactines.

FIGURE 8. Amphoriscus tenax sp. nov. (MNRJ30124—Holotype). A. Oscular skeleton. B. Tangential section of the cortex (arrowheads point to cortical triactines). C. Cross section. D. Cross section showing subatrial triactines (white arrowhead) and the apical actines of the atrial tetractines (black arrowhead). E. Subatrial tetractine (arrowhead). F. Tangential section of the atrium. cx = cortex, at = atrium.

FIGURE 9. Diactines and anchor triactines of Amphoriscus tenax sp. nov. A–D. MNRJ30124 (Holotype). E–H. UFRJPOR5976 (Paratype). A. Diactines I and II. B, C. Distal jagged tip of diactines II. D. Tuft of anchor triactines (arrowhead), most of them broken. E. Tuft of anchor triactines, with detail of the hooks in F. G, H. Root-tufts at the base of the sponge. cx = cortex.

FIGURE 10. Amphoriscus tenax sp. nov. (UFRJPOR5976—Paratype) in SEM.A, B. Dense root-tufts of anchor triactines at the base of the sponge. C. Detail of the root-tufts. Detail of the hook-shaped paired actines of the anchor triactines.

FIGURE 11. Amphoriscus tenax sp. nov. (MNRJ30124—Holotype). A. Diactine I. B. Diactine II. C. Cortical triactines. D. Cortical tetractines. E. Subatrial triactine and tetractine. F. Atrial triactine. G. Atrial tetractines. H. Anchor triactine. I. Detail of the paired actines of the anchor triactine.