The Biology of Glass Sponges

New insights into the phylogeny of glass sponges (Porifera, Hexactinellida): Monophyly of Lyssacinosida and Euplectellinae, and the phylogenetic position of Euretidae

“…It is noteworthy, however, that no morphological autapomorphies are known for Lyssacinosida (Mehl, 1992); the taxon is basically defined by a skeletal organization of mainly unfused spicules (a plesiomorphy that also characterizes Amphidiscophora), combined with hexasters as microscleres (the defining autapomorphy of Hexasterophora) (Mehl, 1992). In contrast, members of ''Hexactinosida" (here represented by Sceptrulophora and Iphiteon panicea) possess rigid skeletons composed of fused hexactine megascleres (dictyonal frameworks) in addition to loose spiculation (see Leys et al, 2007). The position of I. panicea as the sister taxon to Lyssacinosida raises the possibility that dictyonal frameworks were inherited from the last common ancestor of Hexasterophora and subsequently lost in the lineage leading to Lyssacinosida.…”

“…The position of I. panicea as the sister taxon to Lyssacinosida raises the possibility that dictyonal frameworks were inherited from the last common ancestor of Hexasterophora and subsequently lost in the lineage leading to Lyssacinosida. Although the occurrence of ''basidictyonal frameworks" as attachment structures in many lyssacinosidans (see Leys et al, 2007) might provide some support for this idea, homology of these structures to true dictyonal frameworks is questionable, and reasons for a reversal to the ancestral type of skeletal organization are hard to imagine. It is indispensable to determine the phylogenetic positions of additional non-sceptrulophoran dictyonal taxa such as Aulocalycoida, Lychniscosida, and Dactylocalyx in order to reconstruct the evolution of hexasterophoran skeletal organization.…”

“…Glass sponges (Porifera, Hexactinellida) are major components of benthic deep-water communities, and are remarkable for their unique tissue organization, physiology, and aesthetically appealing skeletal morphology (Leys et al, 2007). Leys et al (2007, p. 117) reported 531 described species, but since then this number has increased to 550 (Lopes et al, 2007;Menshenina et al, 2007a,b;Reiswig et al, 2008;Tabachnick and Collins, 2008;, and description of many more new species and even genera is in progress, suggesting that biodiversity of glass sponges is much higher than currently appreciated.…”

Flashing light in sponges through their siliceous fiber network: A new strategy of “neuronal transmission” in animals

“…In hexactinellids, e.g., in Euplectella aspergillum, the interaction between the spicules is even more obvious. Their spicules grow, on average, to larger sizes [20] and often fuse to form a continuous super-scaffold [21] (Figure 2 "radiate" pattern of the spiral type, the spicules are arranged in bundles that have been termed radiating skeletal fibers (rf). Within the fibers, the tissue is organized and harbors the aquiferous canal system (as).…”

Isolated sponge spicules from the late Cambrian Alum Shale Formation (‘Orsten’ nodules) of Sweden

“…Fused skeletons of hexactinellids are the product of a fusion process of their hexactine-based megasclere spicules (Leys et al 2007), and typical hexactinellid megascleres are monoaxons and triaxons. Spicules can be joined with deposition of secondary silica in various ways: by spot-soldering at points of spicule contacts, by formation of anaxial bridges between distant spicules, or by enclosure of rays or spicules within a continuous layer of silica (Leys et al 2007). If so joined, the spicule junctions would have been covered with additional mineral layers during the process because no junction could be clearly identified.…”