Clathrina cerebrum (Haeckel, 1872)

Klautau, Michelle & Valentine, Clare, 2003, Revision of the genus Clathrina (Porifera, Calcarea), Zoological Journal of the Linnean Society 139 (1), pp. 1-62 : 14-16

CLATHRINA CEREBRUM ( HAECKEL, 1872)

Original name: Ascaltis cerebrum Haeckel, 1872

Type locality: Adriatic Sea (Lesina).

Type: PMJ-Inv. Nr. Porif. 156. (Syntype /alcohol). Adriatic Sea (Lesina). Haeckel Collection.

Citations: Bianco (1888); von Lendenfeld (1891); Bid- der (1891); Kirk (1896); Minchin (1896); Breitfuss (1896, 1898, 1935); Dendy & Row (1913); Burton (1933, 1963); Topsent (1934, 1936); Borojevic (1967, 1971); Borojevic & Peixinho (1976); Solé-Cava et al. (1991).

A syntype of C. cerebrum , which is deposited in PMJ, under the registration number Porif 156 Calcarea was examined. Our description matches that given by Haeckel. It is fragmented, mixed with algae.

Colour: Light yellow.

Description: As the cormus is fragmented, it was not possible to determine its organization, or establish the presence of water-collecting tubes. In some parts, the tubes have even collapsed, and it is impossible to distinguish them ( Fig. 9A ).

The wall of the tubes is thin, comprising an irregular meshwork of triactines, tetractines and a few tripods ( Fig. 9B ), which are located only on external tubes. Projecting into the interior of the tubes are the apical actines of the tetractines.

Spicules are equiangular and equiradiate triactines, tetractines, and tripods. Triactines are the most abundant spicules.

The size of the triactines and tetractines is uniform. The actines of the triactines are conical or cylindrical, while the tetractines are always conical. They are straight, with a blunt tip. The apical actine of the tetractines ( Fig. 9C ) is conical, sharp, straight and thinner and shorter than the facial ones. In the distal part, before the tip of the actine, there are sharp spines arranged in 3-4 rows. These spines are directed toward the tip of the actine. Some apical actines, particularly those of young spicules, have only vestigial spines.

Tripods are not abundant, as they are located only on the surface of external tubes. They are approximately the same length as the other spicules, but their actines are much more conical and stout. The centre of these spicules is frequently raised, and their tips are sharp. When the centre is not raised, they are similar to large triactines, but it is still possible to recognize them by the shape of the stout conical actines.

Remarks: Clathrina cerebrum was described by Haeckel (1872) as Ascaltis cerebrum , a species from Lesina, in the Adriatic Sea. Haeckel also identified two varieties of this species in Lesina: gyrosa and decipiens . He described gyrosa as having triactines with the same shape and size, while decipiens was described as having tripods on the external tubes. After Haeckel, however, nobody found specimens corresponding to gyrosa, only to decipiens ( von Lendenfeld, 1891; Kirk, 1896; Breitfuss, 1897; Ferrer- Hernandez, 1918, according to Topsent, 1936).

Dendy & Row (1913) elevated decipiens to the status of species, Leucosolenia decipiens , saying that ‘certain of Haeckel’s so-called Specific Varieties, to which he has already given distinctive names appear to us, after careful consideration of his descriptions, to deserve to rank as separate species’. Topsent (1936) suggested that Haeckel had probably made insufficient observations about some specimens or worked with incomplete material when he described gyrosa, which was then completely abandoned. Topsent said that decipiens was probably the normal state of C. cerebrum (i.e. a sponge with triactines, tetractines with spines in the apical actine and tripods or large triactines on the external tubes), and placed the two species in synonymy.

Unfortunately, Haeckel did not produce a drawing of either the cormus or the spicules of this variety.

As in other clathrinas, the biggest problem we found in the systematics of C. cerebrum was its possible morphological plasticity. We analysed several specimens from the Adriatic and the Mediterranean Seas, including the syntype, which we described above. At the end of our morphological observations, we were astonished by the apparent variability in the cormus organization and in the shape and size of spicules. Even now, we are not sure whether this morphological variability is real or if C. cerebrum is in fact a complex of morphologically similar species.

Previous genetic studies have shown that there are both allopatric ( Solé-Cava et al., 1991) and sympatric ( Klautau et al., 1994) populations, which were previously identified as C. cerebrum . It was observed that these populations were genetically isolated, therefore constituting distinct species, although they were morphologically very similar. Considering these results, we believe that C. cerebrum can probably be split into several new species, but as we observed such morphological variability, we have decided not to split it until a detailed genetic study has been undertaken.

In 1936, Topsent had already observed this phenomenon in the skeleton of C. cerebrum and had even suggested a possible synonymy with L. intermedia and L. proxima , considering that the absence of tetractines in those species was no indication of their specificities. We do not share the same opinion as Topsent in relation to the synonym of C. cerebrum with L. intermedia and L. proxima , principally because these two species are actually from a different genus, Ascaltis . However, we cannot ignore the morphological variability in C. cerebrum , because some of the characters considered important for the identification of this species are variable even among specimens of the same population. The shape of tripods, for example, is very variable. Some specimens have abundant true tripods, while others have only large triactines; a third category has both large triactines and true tripods. Borojevic (1967) has already pointed out the variability in the shape of tripods in C. cerebrum , and shown that the different shapes have probably resulted from different exposures of the specimens to waves. In other words, specimens exposed to strong waves would have more true tripods while less exposed specimens would have a higher proportion of large triactines.

Another very variable character is the presence of spines on the apical actine of the tetractines. In a single specimen, the apical actine can have spines, vestigial spines or even be smooth. A further variable morphological character was in relation to the shape of actines, which can vary from cylindrical to conical in the same individual. Also the size of spicules is very variable.

Although these observations point to high morphological variability, we cannot discount the different proportions of these characters in some specimens. Some individuals have the apical actine predominantly spined or smooth, or abundant true tripods or large triactines; or else more cylindrical or conical actines. We still do not know whether these different proportions have a systematic basis or not. At the moment, however, as we have already said, we will not split C. cerebrum , but we do not consider its previous, cosmopolitan, distribution (Adriatic, Mediterranean, Ternate, Roscoff, South Africa, Brazil and New Zealand) as valid. We think it is better to restrict the distribution of this species to the Adriatic and the Mediterranean Seas, considering our earlier observations that sponges (and particularly clathrinas) do not have a high capacity for dispersal ( Solé-Cava et al., 1991).

We also propose that the specimen PMJ- Inv.Nr.Porif. 156 become a lectotype of C. cerebrum .

Figures

Figure 9. Clathrina cerebrum. A, photograph of the syntype (¥ 10). B, triactines, tetractines and tripods. C, apical actine of a tetractine with spines (arrow). Scale bar = 100 Mm.