Tethya peracuta (Topsent) and T. comorensis n. sp.(Porifera, Demospongiae) from the coral reef of Mayotte (Comores)

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Tethya peracuta (Topsent) and T. comorensis n. sp. (Porifera, Demospongiae) from the coral reef of Mayotte (Comores) a

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Michele Sarà , Giuseppe Corriero & Giorgio Bavestrello

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Istituto di Zoologia , Università di Genova , via Balbi 5, 1–16126, Genova, Italy Published online: 28 Jan 2009.

To cite this article: Michele Sarà , Giuseppe Corriero & Giorgio Bavestrello (1993) Tethya peracuta (Topsent) and T. comorensis n. sp. (Porifera, Demospongiae) from the coral reef of Mayotte (Comores), Bolletino di zoologia, 60:2, 219-224, DOI: 10.1080/11250009309355814 To link to this article: http://dx.doi.org/10.1080/11250009309355814

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Boll. Zool. 60: 219-224 (1993)

Tethya peracuta (Topsent) and T. comorensis n. sp. (Porifera, Demospongiae) from the coral reef of Mayotte (Comores)

MICHELE SARÀ GIUSEPPE CORRIERO GIORGIO BAVESTRELLO

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Istituto di Zoologia, Università di Genova, via Balbi 5, 1-16126 Genova (Italy)

INTRODUCTION Several species of the cosmopolitan genus Tethya (Sarà, 1987) inhabit the coral reefs and especially their lagoon environment. Recent work on reef coral Tethya from Australia (Sarà, 1989), New Guinea and the Maldives (Sarà, unpublished data) includes also field notes on their ecology and biology, features which are relevant in Tethya taxonomy. One of the species collected at Mayotte is T. peracuta (Topsent), hitherto known from a single specimen collected at the Solomon Islands. A large population of this species has been found in the inner lagoon of Mayotte. Its study in situ and in the laboratory has shown unusual morphological and spicular characters, and especially a particular way of external budding. The other species, which has been found in the outer reef in a single specimen, is new for science and has been named T. comorensis.

MATERIALS AND METHODS

ABSTRACT In the coral reef of Mayotte (Comores) two species of Tethya have been found. One, T. peracuta (Topsent), lives densely in a restricted zone in the shallow waters of the lagoon. Its study in situ and in the laboratory has allowed a more complete description showing that this species is characterized by peculiar morphological and spicular characters and also by a special type of external budding. The other species found in the outer reef, T. comorensis, is new for science.

A dense population of T. peracuta was found in a restricted site of the inner part of the lagoon of Mayotte. This site lies 100 m off the shore of Mayotte near the locality of N. Goujan, on the inner board of a reef. Tethya specimens were found among dead coral fragments and branches, generally on their under surfaces, at 10-30 cm below a 0.9 m tide level. Some specimens were photographed in situ and collected by hand in April 1988. The under surfaces of the dead corals are inhabited by several sponges, including boring clionids and other invertebrates such as a very common ascidian. A single specimen of Tethya comorensis was collected in the outer external reef of Mayotte, at 7 m of depth by diving, about 10 km far from the T. peracuta site. All the collected specimens were fixed in ethanol and studied according to the methods of sponge taxonomy. Slides were prepared of dissociated spicules and transversal sections of paraffin-embedded sponges, stained with hematoxylin-eosin or unstained, to study their spicular arrangement and cortical structure. Electron micrographs at SEM (115 Philps) were prepared for some spicules. The holotype of Tethya comorensis and a specimen of T peracuta have been deposited in the Natural History Museum of Genova (Italy) (MSNG). The other specimens of T. peracuta and the slides are in the first author's collection (Institute of Zoology, University of Genova, Italy).

TAXONOMIC ACCOUNT TETHYIDAE Gray, 1867

KEY WORDS: Tethya - Sponges - Coral reef - Budding - Comores. ACKNOWLEDGEMENTS We would like to thank Giulio Relini, Marco Relini and Fiorella Ciferri for help in collecting and photographing in situ the specimens. The GRSTS of Florence organized the expedition in which the first of the authors partecipated. We are indebted to Alessandro Pellerano for technical assistance in drawings. This work has been financially supported by M.U.R.S.T. 40% and 60% funds.

(Received 28 July 1992 - Accepted 21 September 1992)

Tethya Lamarck, 1815

Tethya peracuta (Topsent) Donatia lyncurium auctorum, Dendy 1916, p. 262. Donatia japónica var. peracuta Topsent 1918, p. 564. Donatiaperacuata (Topsent), Burton 1924, p. 1035. Description - Shape: spherical in the small specimens to hemispherical, rather irregular in the larger specimens. An example of the high plasticity of the sponge morphology in relation to the microenvironmental conditions of hydrodinamism and substrate is given by Ma 50-1 (Fig. 1). This specimen is hemispherical, rather

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Fig. 1 - Details of structure and spicular arrangement in Tethya peracuta (a, b) and T. comorensis (c, d). a, transversal section of the peracuta specimen 50-10 showing the thin hispidation on the external cortex (arrows); b, transversal section of the peracuta specimen 50-1 with the centre marked by a double nucleus (arrows); c, transversal section of comorensis showing the cortical lacunes (arrows); d, spherasters distribution around a cortical lacune of comorensis. Bar, 250 |xm.

irregularly elongated. The centre from which the bundles of styles radiate is situated near the sponge basis and is marked by a double nucleus formed by concentrically arranged accessory styles. Only a part of the bundles, following the elongated axis of the sponge, is regularly developed. Some bundles are bent in their distal tract. The cortex is regularly developed but remarkably poor in spherasters in the upper part of the sponge and reduced to a thin coat on the sides. Size (diameter): 0.5-2 cm. Colour (in life): cortex bright ochreous to grayish, medulla dark brownish. Surface (Fig. 2a, b): smooth or with flattened contiguous papillae. Consistency: moderately hard, little compressible. Cortex: in the living large specimens also 2 mm thick, but in the fixed material 0.5-1 mm thick. Only in some specimens are small subdermal lacunes between the bun-

dles of styles visible. The cortex is clearly separated from the medulla. The external surface is coated by a sheet of pigmented amoebocytes and lacks the dense layer of micrasters usual in Tethya. There is a thin hispidation by small styles (Fig la). In the cortex several spherasters and scattered micrasters are generally found. Oscula were not observed. Spiculation (Fig. 3): styles (strongyloxeas): the main category form radiating bundles, sometimes bent or spirally curved, which in the cortex diverge in a corymbus-like shape. Smaller, thinner and vertically arranged accessory styles accompany the bundles and form a continuous hispidation on the surface of the sponge. They also fill the interstices between the bundles in the medulla running parallel to these but in the upper part also in an oblique and confused way. In some specimens they are arranged in concentric layers and perpendicularly to the main styles, constituting a small

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Fig. 2 - Tethya peracuta, external morphology. Arrows indicate the flattened papillae (a), the anchoring filaments (b), a spherical bud (c) and an elongated bud attached to the mother sponge by a filament (d). Bar, 1 mm.

nucleus (about 0.5 mm in diameter) around the bases of the bundles. Main styles: 800-1300 ^m; small, accessory styles: 250-700 \im. Megasters: spherasters situated mainly in the outer cortex and in the outer medulla. More scattered, or in small groups and rows in the middle and inner cortex. Sizes and shapes very variable. D (diameter) = 40-70 ¡xm, but in a group of specimens also 50-80 \im in the cortex and 10-40 \im in the medulla, R/C (length of the ray/ diameter of the center) = 0.7-1 (less frequently 0.4-0.5) in the cortex and 0.6-1 (less frequently 0.2-0.3 or 1-1.5, especially in the small spicules) in the medulla. Some small spherasters show reduced rays sometimes transformed into thin spines. Asters of the chiaster-tylaster type were found in considerable numbers in spicule slides of some specimens, but have been considered abnormal spicules probably derived from the spherasters. They are likely placed in the external layer of the medulla among the normal spherasters, comparable in size to the smaller ones of this category. The numerous, about 12, apically truncated,

spined and sometimes slightly knobbed rays may be cylindrical or conical. The centre is generally very developed but sometimes small. D = 10-20 ^im; R/C = 0.2-1. Micrasters: oxyasters to chiasters scattered in the whole sponge and not building the usual thick layer on its surface. With numerous slender elongated and roughened rays, sometimes irregularly bent or forked, without centre. D = 8-15 um, the larger sizes more frequent in the medulla (Fig. 4). Material - 21 specimens (Ma 50 and Ma 71), Mayotte lagoon, 10-30 cm, 4/4/88, leg. M. Sarà and F. Ciferri. Reproduction - The majority of the large specimens show external buds (Fig. 2c, d). These are produced, in small numbers, by Tethya larger than 1 cm. They grow large, first in contact with the mother sponge and after in proximity with it, also some cm distant, attached to it by filaments and adhering to the substrate (Fig. 5). The largest buds of 2-4 mm in diameter gradually transform into young Tethya. The buds have a more yellowish

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30/jm

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Fig. 3 - Tethya peracuta: A, styles; B, cortical spherasters; C, medullar spherasters; D, abnormal asters (occurring oily in some specimens); E, micrasters; F, transversal section with the skeletal pattern (styles and megasters).

colour than the adult sponges. Sexual reproduction phases were found only in one specimen, with oocytes in the medulla. Ecology - The sponge lives in the shallow waters of lagoon pools a few cm deep, subjected to high temperatures, tidal currents and heavy sedimentation. It is protected by direct sunlight through its being on the under surfaces of dead coral fragments. It is adapted against detachment from the substrate by anchoring filaments and outgrowths (Fig. 5). Also the flattened, hemispherical shape of the larger specimens and the special form of budding with large buds anchored near the mother sponge may be considered adaptations of T. peracuta to its peculiar habitat. The species has been found sparsely distributed in a single site of the Mayotte lagoon. Remarks - Tethya peracuta was found in a single specimen from the Solomon Islands, 10-14 fathoms deep, coming from the Percy Sladen Trust Expedition and described by Dendy (1916) as Donada lyncurium auctorum. But Topsent (1918) assigned the specimen to Donatia japónica and, aware of its singularity, to a new variety, peracuta. Subsequently Burton (1924) considered peracuta a good species, but erroneously named it D. peracuata. The type of the species is presently represented by the

slide (section) 1925: 11: 1: 1169 in the collection of the BMNH, which corresponds to the specimen CXX 2 c, described by Dendy from the Solomon Islands. Also the small specimen, 8 mm in diameter, from the Sealark Expedition 1920: 12: 9: 81 al, coming from the Indian Ocean, and deposited in the BMNH Tethya collection, should be attributed to T. peracuta. The series of specimens found in the Mayotte lagoon shows clearly, after comparison with the peracuta type, that it belongs to this species on the basis of the striking similarity of the spicular characters, also in the details. Budding is not described for the holotype, and it is not possible to compare this character, which is very representative, in its modes, of the Comores population. The study of this population shows that T. peracuta is provided with characters which are unusual in the genus Tethya. More relevant peculiarities are, with regard to the general morphology, the abundance of anchoring filaments often accompanied by attached buds and, to the spiculation, the occurrence of spherasters with thin reduced rays, the oxyaster type of cortical micraster, the aberrant asters of some specimens and the lack of a dense layer of micrasters on the surface of the sponge. An outstanding reproductive peculiarity is the special type of external budding with few and large buds which grow as young sponges in narrow contact with the mother sponge. This may be considered an adaptive device to a severe habitat in which Tethya may survive only in a few favourable places and where it must avoid its asexual propagules being carried away from these places by the strong tidal regime and wave movements. The production of few buds, which grow very large in contact with the mother, may be considered a parental care and a form of extreme K strategy. Extreme, because no other Tethya, as far as we know, shows a similar protection against the dispersal of external buds. However, other Tethya species differ in the number and dimensions of their buds, thereby suggesting different reproductive strategies. The reduction of the spherasters to spheres with spines or naked spheres, is an abnormal character which occurs also in Tethya comorensis and, abnormally (Bergquist & Kelly Borges, 1991) or also normally (Burton, 1924; Sarà, unpublished data) in other Tethya species from Australia and Tasmania. This may be of Zoogeographie interest showing that the Tethya of the Comores have some affinity with the austral Tethya.

Tethya comorensis sp. n. Description - Shape: spherical. Size: 1 cm. Colour (in life): cortex orange, medulla brown. Surface: with conules, partially covered by sediment. Cortex: 1 mm thick (on fixed material), with large subdermal lacunes (Fig. lc, d). Oscules are not visible. Consistency: moderately hard, little compressible.

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Fig. 4 - Tethya peracuta, micrasters (electromicrographs). Bar, 1 \im.

Fig. 5 - Tethya peracuta: sketch (from a photograph) of a specimen in situ with attached buds and anchoring filaments.

Spiculation (Fig. 6). Styles (strongyloxeas): 300-1200 x 3-15 mji. Many small and slender styles occur in addition to the main styles. In the main category, the head of the styles is often well developed, 8 (im thick but not well separated from the axis of the style. Generally, the main styles form the radiate bundles which end in the conules, while the slender accessory styles fill somewhat confusedly the interstices left in the medulla between the bundles. Megasters: spherasters D (diameter) = 45 urn in the cortex, 15-35 um in the medulla. R/C (length of the ray / diameter of the centre) = 0.3/0.7 (the small spherasters also > 1). Many spherasters with rays reduced to thin spines and sometimes very short or totally lacking. The spherasters are then reduced to spheres. In the cortex, the spherasters are distributed as monolayers on the surface, around the lacunes (Fig. 1 b) and the main channels and at the boundary between the cortex and the medulla. In the medulla, the spherasters are diffuse everywhere but very heterogeneous in size with a high percentage of small spicules. Some chiasters-tylasters, 12-15 |xm with developed centre (R/C = 1) found in spicule slides from

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Type specimen - One specimen, Ma 70 (MNSG C.E. 48528), Mayotte, outer reef, 7 m, 4/4/88, leg. M. Relini.

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fC

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10unn

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Remarks - Tethya comorensis is distinguished from T. peracuta by its external aspect, development of cortical lacunes, spheraster shape, size and distribution, occurrence of a micraster cortical layer, micraster size, ecology, and absence of buds. In particular, the differences in the cortical structure and in the spheraster shape, size and distribution, are important for considering T. comorensis a different species from T. peracuta, according to the general criteria of Tethya taxonomy. On the other hand, T. comorensis shows two peculiar features which occur also in some specimens of T. peracuta: the aberrant chiaster-tylaster type and the reduced spherasters, this latter character in a more pronunced way. These abnormal, non-functional similar markings, together with the similarities in the micraster shape and especially in the filling of the medulla by the small styles, indicate that the two species are probably akin. No obvious relationship can be found with other Tethya. Etymology - The name derives from the locality where the species was discovered.

REFERENCES

Fig. 6 - Tethya comorensis n. sp.: A, styles; B, cortical spherasters; C, medullar spherasters: D, abnormal asters; E, micrasters; F, transversal section with skeletal pattern (styles and megasters).

the medulla are probably aberrant and reduced spherasters. Micrasters: oxyasters-chiasters, 7-10 \im, with numerous slender roughened rays, variable in their more conical or cylindrical shape, sometimes with a small swelling at the tip. Generally without centre, but in some cases with a small one. They are similar in the cortex and in the medulla and more numerous in the outer cortical layer.

Bergquist P. R., Kelly-Borges M., 1991 - An evaluation of the genus Tethya (Porifera: Demospongiae: Hadromerida) with description of new species from the Southwest Pacific. Beagle, 8: 37-72. Burton M., 1924 - A revision of the sponge family Donatiidae. Proc. Zool. Soc. Lond. 15: 1033-1045. Dendy A., 1916 - Report on the Homosclerophora and Astrotetraxonida collected by H.M.S. Sealark. Trans. Linn. Soc. Lond. 17: 227-271. Sarà M., 1987 - A study on the genus Tethya (Porifera, Demospongiae) and new perspectives in sponge systematics. In: J. Vacelet & N. Boury-Esnault (eds), Taxonomy of Porifera. Springer Verlag, Berlin, pp. 205-225. Sarà M., 1989 - Australian Tethya (Porifera, Demospongiae) from the Great Barrier Reef with description of two new species. Boll. Zool., 57: 153-157. Topsent E., 1918 - Eponges de S. Thomé. Essai sur les genres Spirastrella, Donatia, et Chondrilla. Arch. Zool. exp. gén., 57: 535-618.