Evolution & Systematics

Generally, Poriferans play an important role in the determination of metazoan phylogeny (Leys and Hill 2012). Although structurally simple, the complex extracellular matrix (ECM) present in the sponge body provides evidence for the development of the ECM as a common ancestral feature that brings together all metazoans (Kamerling and Carvalho de Souza 2011).

Sponge structure, however, has led to difficulty in determining phylogenetic relationships between themselves, as a result of their simple body plan. This limits the selection of obvious morphological characteristics for in depth analysis (Escobar et al. 2002; Hill et al. 2009).

Several studies have been conducted in order to determine the relationship between different species of Cliona. There has been much confusion and rearrangement regarding Cliona taxonomy, systematics and naming (Schonberg 2000, Zea and Weil 2003). Limited knowledge and lack of in depth morphological and physical descriptions of these sponges have contributed to a poor understanding of Cliona systematics (Schonberg 2000). Identification of Cliona spp. so far has been based on form, type, size, spicule characteristics and arrangement (Escobar et al. 2002; Schonberg 2000).

Atlantic, Mediterranean and Indo-Pacific species of Cliona have been grouped together in what is known as the “Cliona virdis complex” (Zea and Weil 2003). This grouping was based on genetic heterogeneity (morphologcal similarities) between the species' involved (C. aprica, C. caribbea, C. langae, C. orientalis, C.varians, C. virdis) (Escobar et al. 2012; Schonberg and de Beer; Zea and Weil 2003).

Recent studies suggest that examining the Symbiodinium and Cliona relationship can reveal information about Cliona phylogeny (Hill et al. 2009). According to Hill et al. (2009) this relationship can be explored by comparing the properties of different symbiont species in each sponge determining whether closely related species  of Cliona have similar symbionts present.

Other traits may aid in determining the phylogeny of Cliona include, the use of molecular data (nuclear and mitochondrial DNA sequences)(Escobar et al. 2012) and comparison of boring patterns and substrate etchings(Calcinai et al 2007).

Little is resolved in terms of Cliona evolution and systematics and further in depth research is required before any certainty, if possible, can be achieved.