Stelletta fibrosa Schmidt 1870

Stelletta fibrosa (Schmidt, 1870)

(Figures 8–9)

Synonyms.

Ancorina fibrosa Schmidt, 1870: 67.

Pilochrota fibrosa (Schmidt, 1870): Sollas 1888: 180. Myriastra fibrosa (Schmidt, 1870): de Laubenfels 1936: 169.? Pilochrota fibrosa var. globuliformis Wilson, 1902: 385.? Stelletta fibrosa var. globuliformis (Wilson, 1902): Díaz 2007: 21.? Stelletta incrustata Uliczka, 1929: 47, figs. 31–35, pl. I, fig. 7.? Stelletta variastra Pulitzer-Finali, 1986: 70, figs. 4–5.

Lectotype. MCZ 8020, Tortugas, Florida, dry, Schmidt material (here designated).

Material. ZMBN 81784, Caracol Reef, 15 m depth.

Additional material examined. Stelletta fibrosa, MCZ 8020, holotype, Tortugas, Florida, dry; ZMAPOR 04585a, Blauwbaai, Curaçao, 10 m; ZMAPOR 12608, Santa Marta, Colombia, 5 m. Stelletta cf. anancora Sollas, 1886, INVPOR 1061, La Guajira, Colombia, 50 m.

Outer morphology (Fig. 8 A–C). Massive, sub–globular sponge, 9 cm of diameter. Color alive is whitish with dark–purple tiny spots mainly concentrated around the oscules. Bottom of the sponge is pure white (Fig. 8 C). Choanosome color alive is cream. In ethanol, cortex and choanosome are whitish. Slightly compressible. Rugose surface. The cortex is thick (3 mm) and lighter than the choanosome. One large oscule (diameter: 1.5 cm) is placed at the top with a brown contractile membrane with whitish spots on it; the oscule leads into a cloaca 5 cm deep where uniporal excurrent canal openings meet (Fig. 8 A–B). Smaller oscules (1–5 mm) are generally surrounded by an elevated thick margin, they are unevenly distributed on the sides; the underlying cloacae are around 2 cm deep (Fig. 8 A–B). Pores are covered with cribriporal plates (ca 1 mm) and are evenly distributed. A few short root–like structures (ca 1 cm) are present at the base of the sponge (Fig. 8 C). The green sponge Amphimedon erina (de Laubenfels) is growing on it. Ophiuroids were found living in the cloacae of the small oscules.

Skeleton (Fig. 8 D). The cortex is composed of radially and densely arranged plagiotriaenes. Subcortical cavities are conspicuous and visible to the naked eye. Plagiotriaenes and oxeas under the cortex are more or less radially arranged; they are not as densely packed as in the cortex. Acanthotylasters are common and present throughout the cortex and choanosome.

Spicules (Fig. 9 A–D). Megascleres: (a) oxeas (Fig. 9 A), large, very slightly bent or straight, length: 660– 1151.4 –1536 µm; width: 7– 30.1 –57 µm. (b) plagiotriaenes (Fig. 9 A), stout, horn–shaped clads, rhabdome length: 511– 1032.9 –1280 µm; rhabdome width: 7– 33.3 –50 µm; clad length: 14– 61.7 –98 µm. (c) anatriaenes (Fig. 9 B), rare, with depressed apex, rhabdome length:? (rhabdomes broken); rhabdome width: 31– 32.5 –34 µm (N=2); clad length: 45– 49.5 –54 µm (N=2). Microscleres: (d) acanthotylasters (Fig. 9 C–D), 4–8 actines, diameter: 7– 11 –16 µm.

specimens from Bocas del Toro and previous records. Measurements of Stelletta incrustata, a possible junior synonym,

are also included. In bold are the museum specimens measured for this study. Means are in bold italics; other values are

ranges; N=30 unless stated otherwise between parentheses. – = not refered; n.f. = not found; n.o. = not observed.? =

missing data.

Habitat in the Bocas del Toro region. Reefs, rare, 15 m depth.

Distribution. As S. fibrosa: Florida, U.S.A. (Schmidt 1870); Curaçao (van Soest 1981); Panama (this study); Colombia (this study). As S. fibrosa var. globuliformis: Puerto–Rico (Wilson 1902).

Remarks and discussion. A thorough revision of the Caribbean Stelletta species is greatly needed but beyond the scope of this study. In the Caribbean, four species of Stelletta share tylasters: S. fibrosa (Schmidt, 1870), S. variabilis (Wilson, 1902), S. kallitetilla (de Laubenfels, 1936b) and S. pudica (Wiedenmayer, 1977). These four species are poorly known.

We have had difficulty to assign a species name to this specimen, never observed before in Panama. The color alive of our specimen (whitish with purple spots) corresponded to that of S. fibrosa from Puerto–Rico (Pulitzer-Finali 1986). This species is unfortunately very poorly described by Schmidt (1870) and the type is not formally identified. However, the original label “ Ancorina fibrosa n. n.” of a dry specimen (MCZ 8020) from the type locality (Tortugas, Florida) strongly suggests that it is type material from the Schmidt collection. This small fragment 1.9 cm long (Fig. 8 E) is here designated as the lectotype of Stelletta fibrosa. The shape of the spicules and the skeleton organization of the Bocas del Toro specimen fitted with the lectotype (Figs. 8 F, 9E-F) and comparative material. A few differences between the lectotype and the Bocas specimen were nonetheless observed: the Bocas specimen had (i) several anatriaenes, (ii) no wavy to strongly bent oxeas and rhabdomes (such as those found in the lectotype), (iii) larger width of triaenes and oxeas and (iv) longer clad lengths. The triaenes and oxeas of the Bocas specimen were also bigger than in our comparative material and any previous descriptions of S. fibrosa (Table 3). Although anatriaenes were absent in the lectotype, they have been found in low numbers in previous records (Wilson 1902; Pulitzer-Finali 1986) and also in our comparative material. Anatriaenes are therefore fairly common in this species. As for the strongly bent oxeas found in the lectotype, we believe they are not diagnostic since these were absent in the comparative material. Tylasters of our specimen had actines with few spines (Fig. 9 C–D), whereas these were completely smooth in the lectotype (Fig. 9 F). To conclude, the size of the megascleres remained the main difference between our material and previous records; it might be explained by the size of our specimen, the largest of this species described so far. The lectotype and ZMAPOR 12608 both had abundant sand grains incorporated in the ectocortex (Fig. 8 E), while ZMAPOR 04585a had few and our specimen none (Fig. 8 D).

Examination of INVPOR 1061 from Colombia, identified as S. fibrosa var. globuliformis (Díaz, 2007), showed that it had different sizes of triaenes, the largest size having significantly longer and thinner clads than our S. fibrosa specimens. With respect to its triaenes and its external morphology (massive spherical, single osculum on top, surface with numerous foreign material), it appeared to us similar to S. anancora. But a revison of this species is required to confirm this. For the moment, we agree with Pulitzer-Finali (1986) that S. fibrosa and S. fibrosa var. globuliformis are the same species: their spicule measurements match. This species could therefore have an encrusting or a massive spherical shape. S. variabilis (Wilson, 1902) appears to be a valid species, different from S. fibrosa: orthotriaenes have long clads, there are smaller oxeas II in cortex, and common anatriaenes. Following this, S. fibrosa identified by Wells (1960) is rather S. variabilis (as noted before us by Pulitzer-Finali (1986)). As for S. pudica, it has no or only few regressed plagiotriaenes (Wiedenmayer 1977; Pulitzer-Finali 1986).