Hexactinellida

Protospongia (Cambrian-Ordovician)

Siphonia (Cretaceous-Tertiary)

Hydnoceras (Silurian-Carboniferous)

Protospongia (Cambrian-Ordovician)

Hydnoceras (Silurian-Carboniferous)

Prismodictya (Devonian-Carboniferous)

Prismodictya (Devonian-Carboniferous)

Hexactinellida Images

Astraeospongium (Silurian-Devonian)

Figure 11.3 Some examples of the main groups of sponges: Archaeoscyphia (x0.25), Siphonia (x0.4 and 0.8), Protospongia (x0.4), Hydnoceras (x0.25), Prismodictya (x0.6), Rhaphidonema (x0.8), Corynella (x0.8) and Astraeospongium (x0.4).

Astraeospongium (Silurian-Devonian)

Figure 11.3 Some examples of the main groups of sponges: Archaeoscyphia (x0.25), Siphonia (x0.4 and 0.8), Protospongia (x0.4), Hydnoceras (x0.25), Prismodictya (x0.6), Rhaphidonema (x0.8), Corynella (x0.8) and Astraeospongium (x0.4).

The relationships among the three major groups of Porifera are obscure. Analyses of poriferan morphology and structure, cytology and molecular biology suggest that, first, sponges are a para-phyletic grouping (Sperling et al. 2007) and, second, that the Calcarea and Hexactinellida form monophyletic groups that are close to the base of the Eumetazoa. The Demospongea is more basal (Fig. 11.4).

Figure 11.4 Sponge paraphyly. (a) The more traditional view presenting both the eumetazoans and poriferans as monophyletic groups; feeding strategies cannot be polarized since all the outgroups are non-metazoan. (b) If, however, poriferans are paraphyletic and calcisponges are more closely related to eumetazoans then the water canal system is a primitive character and the gut is more derived.

Figure 11.4 Sponge paraphyly. (a) The more traditional view presenting both the eumetazoans and poriferans as monophyletic groups; feeding strategies cannot be polarized since all the outgroups are non-metazoan. (b) If, however, poriferans are paraphyletic and calcisponges are more closely related to eumetazoans then the water canal system is a primitive character and the gut is more derived.

Hexactinellida Images
Figure 11.5 Main categories of spicule morphology. Magnification approximately x75 for all, except microscleres which are about x750.
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