Filigorgia schoutedeni ( Stiasny, 1939 ) Sánchez, 2007

Sánchez, Juan A., 2007, A new genus of Atlantic octocorals (Octocorallia: Gorgoniidae): systematics of gorgoniids with asymmetric sclerites, Journal of Natural History 41 (9 - 12), pp. 493-509 : 504-506

Filigorgia schoutedeni ( Stiasny, 1939) com. nov.

Leptogorgia schoutedeni Stiasny 1939, p 106 .

Leptogorgia schoutedeni: Grasshoff 1988, p 115 .

Why are surface layer sclerites so important?

Since surface sclerites modify colony flexion by preventing compressibility of the outer cortex when they contact each other and help the colony to resist drag forces and flow ( Lewis and Von Wallis 1991), a characteristic on which natural selection can act. Their interaction with the environment has produced a great array of forms and these structures are more variable than polyp or axial sheath sclerites ( Sánchez et al. 2003b; Sánchez 2005). It is important to note, however, that the function of surface sclerites can be homoplasious and similar trends exist in many genera (e.g. Figure 12E, G ). Nonetheless, surface sclerites can be helpful for supra familial classification and provide a better understanding of octocoral phylogeny in general.

It has been demonstrated that colonial characters such as branching and overall colony form are highly homoplasious, providing multiple analogous forms within the family Gorgoniidae , which should not be considered as characters for classification (e.g. whip like, sea fan, pinnate, etc.). For example, Bayer (1953) first proposed convergent evolution for gorgonian colony architectures such as sea fans ( Pacifigorgia spp. and Gorgonia spp. , Figure 2 ) and sea leaves ( Phycogorgia spp. and Phyllogorgia spp. , Figure 2 ). Bayer’s hypothesis for sea fans has been corroborated with mitochondrial ( Sánchez et al. 2003b; Sánchez 2004) and nuclear DNA sequences ( Aguilar and Sánchez 2007a, 2007b). Pinnate morphologies such as Pseudopterogorgia spp. and Pinnigorgia spp. seemed to have evolved their branching morphologies separately (e.g. Figure 1 ). Surface layer sclerites under the resolution of SEM provided a good character to differentiate gorgoniid clades with very similar external characters.

The molecular contribution

The corroboration of Filigorgia as a genus apart from Leptogorgia is another example where recent molecular results have improved our understanding of some morphological characters ( Fukami et al. 2004). The validation of the genus Filigorgia is also supported with previous molecular studies. Mitochondrial DNA sequences from the mut-S homolog gene (MSH1) show additional classification problems within the Gorgoniidae (A. LePard and S. France, personal communication). Although focusing on Leptogorgia , they found that supposed Leptogorgia ‘‘outgroups’’ such as Pseudopterogorgia , Pacifigorgia , and Eugorgia were intermingled with various clades of Leptogorgia , which clearly show that some of the African fauna from Leptogorgia sensu lato are not reciprocally monophyletic. Williams and Lindo (1997) provided a detailed comparison of spindles of Leptogorgia spp. with several gorgoniid genera showing that scaphoid sclerites are not the best character to differentiate gorgoniid genera due to their high similarity, particularly with Indo-Pacific species of Pseudopterogorgia . Although it was not a goal of this paper, it was clearly noticed that Pacific and Atlantic Pseudopterogorgia spp. surface sclerites were not homologous (e.g. Figures 3A versus 4E), and deserve further study.

Finally, it is important to note that some genera assigned to the Gorgoniidae need careful revision (hopefully both taxonomical and molecular) in order to be unambiguously assigned to this family, such as in the case of Hicksonella and Rumphella ( Grasshoff and Alderslade 1997) , as well as Adelogorgia and Eunicella , whose sclerites are not likely homologous to the species presented here. In addition, there are a number of plexaurid genera such as Swiftia ( Goldberg 2001) and Plexaurella that, with recent molecular analyses ( Sánchez et al. 2003b; Wirshing et al. 2005; McFadden et al. 2006), have been found to resemble some gorgoniids.

Figures

Figure 1. Phylogenetic hypothesis (maximum likelihood estimated phylogram) of Atlantic gorgoniids, modified from Aguilar and Sánchez (2007a, Figure 4A). The ‘‘Undescribed octocoral’’ refers to the new genus and species described below. Above node letters: A, support corresponding to values.90 in 100 bootstrap maximum likelihood replicates, 1000 bootstrap values in maximum parsimony together with values over 0.9 posterior probabilities of Bayesian inference; B, support corresponding to values.90 in 100 bootstrap maximum likelihood replicates but lesser values for maximum parsimony or Bayesian inference (,70 or 0.70, respectively); C, support corresponding to values,70 in 100 bootstrap maximum likelihood replicates but higher values for maximum parsimony or Bayesian inference (,90 or 0.90, respectively). Character mapping: grey bars, gorgoniids with scaphoid sclerites (Clade 1); open bars-dotted, gorgoniids with capstan-derived sclerites (Clade 2); grid bars, gorgoniids with asymmetrical spiny sclerites (Clade 3); black bars, gorgoniids with long and spiny spindles (Clade 4). Scale in substitutions per site. *Pinnigorgia and Muriceopsis are also supported by a complete compensatory base change in their RNA secondary structure, a rare evolutionary event (see Aguilar and Sánchez 2007a).

Figure 2. Diverse species of gorgoniids. (A) Phyllogorgia dillatata (Brazil, USNM 5252); (B) Gorgonia mariae (Carrie Bow Cay, Belize); (C) G. ventalina (San Salvador, Bahamas); (D) Pacifigorgia elegans (Brazil, USNM 50953); (E) P. agassizi (Colombia, Invemar collection); (F) Pseudopterogorgia sp. (Carrie Bow Cay, Belize); (G) Pterogorgia anceps; (H) Leptogorgia stheno (Bocas del Toro, Panama´).

Figure 3. SEM stereopairs and/or images of sclerites from the surface coenenchyme layer of species of gorgoniids with scaphoids sclerites (Clade 1). (A) Pseudopterogorgia acerosa (Tobago), stereopair; (B) Gorgonia mariae Bayer, stereopair (USNM 1007505); (C) Olindogorgia macgravi (Bayer); (D) Pterogorgia anceps (personal collection); (E, F) Pterogorgia citrina (USNM 1007406). Scale bars: 0.01 mm (A, C, E, F); 0.003 mm (B); 0.04 mm (D).

Figure 12. Surface sclerites of several gorgonian corals. (A–D) Tobagorgia hardyi new species; (E, F) Filigorgia schoutedeni (Stiasny); (G) Leptogorgia virgulata Linnaeus. (A–F) SEM stereopairs. Scale bars: 0.02 mm.