Sycettusa flamma (Poléjaeff, 1883)

(Figs. 36–38; Table 15)

Synonyms: Amphoriscus flamma — Poléjaeff 1883: 49; Topsent 1891: 12; Mello-Leitão et al. 1961: 2. Grantessa flamma — Dendy & Row 1913: 752; Borojević & Peixinho 1976: 1011. Sycettusa flamma — Muricy et al. 2011: 29.

Type locality: Salvador, Bahia State, Brazil.

Material examined: MNRJ2040, Búzios Island, Ilhabela, São Paulo State, Brazil, depth 10 m, coll. E. Hajdu, 07/II/1999. MNRJ30130, Celada, São Sebastião Island, Ilhabela, São Paulo State, Brazil, depth 8 m, coll. E. Hajdu & M. Carvalho, 01/ V /2002. UFRJPOR7006, Saco da Ponta Grossa, São Sebastião Island, Ilhabela, São Paulo State, Brazil, depth 6 m, coll. F. F. Cavalcanti & V. Padula, 03/XII/2008.

Comparative material examined: Holotype of Sycettusa flamma — BMNH.1884.4.22.25 (slides), off Salvador, Bahia, Brazil, Challenger Exp., shallow water, September 1873.

Colour: White or beige in life and beige in ethanol (Figs. 36A; 37A).

Morphology and anatomy: Sponge body formed by two or three large tubes connected at the base, with apical and wide oscula ornamented with a well-developed crown of trichoxeas (Figs. 36A; 37A, B). The external surface is heavily hispid due to the numerous diactines projecting through the cortex. The atrial cavity is wide and hispid, with the apical actines of the atrial tetractines projecting into its lumen. Aquiferous system syconoid, but rather irregular (more evident in the specimen MNRJ2040), with narrow, elongated choanocyte chambers that seem to branch distally (Figs. 36B; 37C, D).

The skeleton of the oscular crown is composed of long trichoxeas and large diactines, supported by tetractines and rare triactines (Fig. 37B). The cortical skeleton is formed by tangential triactines (Fig. 36C) and large diactines that protrude perpendicularly through the surface and cross the body wall, occasionally reaching the atrium. The subcortical skeleton consists in a layer of pseudosagittal triactines (Fig. 36D) and the subatrial skeleton in triactines and rare tetractines (Fig. 36E). The choanosomal skeleton is inarticulate (Figs. 36B; 37C, D), as is typical of the genus. In the specimen MNRJ2040, which has a thicker body wall than MNRJ30130, a single intermediate layer of triactines is present in the choanosome (Fig. 36B). The atrial skeleton is composed of several tetractines and rare triactines (Fig. 36F), arranged with the paired actines curved towards the osculum and the unpaired actine pointing to the base of the sponge (Fig. 36F). Fragments of trichoxeas are common in the cortical and atrial skeletons (Fig. 36D, E —inset).

Spicules (Table 15):

Trichoxeas: Long, thin, cylindrical, and usually broken. Size:>3,000.0/7.0 µm.

Diactines: Large, straight or slightly curved. The distal tip is usually lanceolate, while the proximal tip is sharp and thicker (Figs. 36D inset; 38A). Size: 2,341.3 (±519.3)/71.5 (±10.4) µm.

Cortical triactines: Slightly sagittal, with slightly conical and sharp actines. The unpaired actine is straight and of similar length or slightly shorter than the paired ones, which are outwardly curved (Fig. 38B). Size: paired— 226.8 (±45.2)/16.3 (±3.9) µm; unpaired—226.3 (±50.5)/18.8 (±2.8) µm.

Subcortical triactines: Pseudosagittal. Actines are slightly conical, with sharp tips. The shortest paired actine (paired 1) is curved, sometimes undulated, while the unpaired actine is straight and the longest paired actine (paired 2) is almost straight or undulated (Fig. 38C). Size: paired 1—265.0 (±50.1)/20.3 (±3.8) µm; paired 2—357.0 (±66.7)/20.8 (±3.6) µm; unpaired—169.0 (±41.8)/21.0 (±2.8) µm.

Subatrial triactines and tetractines: Sagittal, with conical to slightly conical and sharp basal actines. The paired actines are curved towards the unpaired one, which is straight or undulated, and longer and thicker than the paired ones (Fig. 38D, E). When the triactines are displaced into the choanosome (MNRJ2040), they become less sagittal, and the unpaired actine is shorter, more similar in length to the paired ones. The apical actine of the tetractines is very short and thin, straight, conical, and sharp. Triactines size: paired—309.0 (±62.3)/24.3 (±4.3) µm; unpaired—512.0 (±112.2)/27.2 (±5.2) µm. Tetractines size: paired—262.9 (±46.3)/20.4 (±4.0) µm; unpaired— 413.3 (±77.5)/23.3 (±3.1) µm; apical—41.2 (±9.5)/7.6 (±1.5) µm.

Atrial triactines and tetractines: Slightly sagittal (but strongly sagittal near the osculum), with cylindrical and sharp basal actines. The paired actines are curved and generally similar in size to the unpaired one, which is straight (Fig. 38F). The apical actine of the tetractines is shorter than the basal ones, cylindrical, curved, laterally compressed, and sharp. Triactines size: paired—201.1 (±43.9)/9.3 (±1.2) µm; unpaired—191.1 (±61.5)/11.4 (±1.3) µm. Tetractines size: paired—237.5 (±43.1)/9.8 (±0.8) µm; unpaired—241.5 (±57.5)/11.8 (±1.4) µm; apical—105.8 (±15.5)/9.3 (±1.1) µm.

Ecology: Specimens were collected in a hole inside a vertical wall or exposed to sunlight. Sediment was accumulated among the long cortical diactines of the specimens, where organisms such as tubiculous and errant polychaetes, bryozoans, bivalves, ophiuroids and a dromiid crab were found.

Geographic distribution:Azores Canaries Madeira ecoregion— Canary Islands, North Atlantic Ocean (Topsent 1891), Spain. Amazonia ecoregion— Amapá State (Borojević & Peixinho 1976), Brazil. Eastern Brazil ecoregion— Bahia State (Poléjaeff 1883), Brazil. Southeastern Brazil ecoregion—São Sebastião and Búzios Islands (Ilhabela), São Paulo State (present study), Brazil.

Remarks: The specimens fit well Poléjaeff’s (1883) description of S. flamma from Salvador, Bahia, later reported from the northern Brazilian coast by Borojević & Peixinho (1976). The main difference is that the original description did not mention atrial triactines, only tetractines. However, upon examining the holotype, we found rare atrial triactines. Poléjaeff (1883) also did not report triactines in the middle of the choanosome, but we observed these spicules both in the holotype and in one of our specimens (MNRJ2040). Conversely, these spicules were absent in specimen MNRJ30130, which has a thinner body wall, suggesting that their presence may be related to body wall thickness, likewise the desorganised zone of Paraleucilla (Lanna et al. 2017). When present, these triactines form only a single layer, maintaining the inarticulate nature of the choanosomal skeleton, a feature characteristic of the genus.

Our specimens, as well as those from Amapá (northern Brazil) described by Borojević & Peixinho (1976), exhibit overall smaller spicules compared to the holotype (Table 15). However, spicule shape and other morphological features remain consistent with the holotype of S. flamma. Thus, the geographic distribution of S. flamma is extended here from the northern and northeastern regions to the southeastern Brazilian coast, with notable variability in spicule dimensions across its range.

In our phylogenetic tree, the C-LSU sequence of S. flamma was not within the main clade of Sycettusa species, formed by S. hastifera, S. simplex (Jenkin, 1908), S. hirsutissima Van Soest & De Voogd, 2018, and S. stauridia (Haeckel, 1872). Instead, S. flamma clustered with Sycon conulosum, Leucilla antillana, and Paraleucilla perlucida, which belong to the families Syconidae and Amphoriscidae. This result agrees with previous findings indicating the non-monophyly of the genus Sycettusa and the family Heteropiidae (e.g. Alvizu et al. 2018).