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SENOWBARI-DARYAN, Baba:Die systematische Stellung der thalamiden Schwämme und ihre Bedeutung in der Erdgeschichte1990. [in German] – 326 pp., 70 figures, 18 tables, 63 plates. ISBN 978-3-923871-42-1 Euro 50.00 |
Segmented sponges (»Sphinctozoa« STEINMANN, »Thalamida« LAUBENFELS) appear for the first time in the Cambrian and range up to modern times. During the Permian, Triassic and the Cretaceous they were an important group of frame builders within the reefs. Vaceletia crypta (VACELET) is the only known recent species of segmented sponges. Vaceletia lives within cryptic biotops on reef slopes in the Indian and Pacific Ocean, in water depths of 15-40 m.
Because of the polyphyletic nature of the segmented sponges, the terms »Sphinctozoa« or »Thalamida« can not be used as a taxonomic term. This problem is discussed in chapters 2 and 3.
Morphologic and structural features of segmented sponges (spicular skeleton, mineralogy and microstructure of the rigid skeleton) are discussed in chapter 4. Because of the lack of a spicular skeleton in most genera of segmented sponges, especially in Paleozoic genera, morphologic features of segmented sponges must still be used for describing and systematic classification of this group of animals.
Spicules in some »typical« Triassic and Permian sphinctozoan sponges are described here for the first time. Such spicules are mainly monaxon macroskleres, but rarely include other shapes. Microscleres have been found only in very rare eases. The present composition of all proven spicules is calcite. However, most evidence points to a primary siliceous composition for the spicules. Consequently the affiliation of these sponges, and most probably that of most or all Paleozoic and Mesozoic genera of sphinctozoan sponges, is with Demospongea. In addition to these »true« spicules, other structures here termed »pseudospicules« have been found in some Triassic, Jurassic and Cretaceous segmented sponges. These structures, which have been described as spicules, are interpreted as primary cavities that may have been filled with an organic (not mineralized) substance during lifetime of the sponges.
The spicular skeleton of segmented sponges appears to have been the primary one and the rigid calcareous skeleton a secondary one. The rigid skeleton was an exoskeleton. The soft tissue of segmented sponges lived within the rigid skeleton.
Rigid skeletons of segmented sponges consist of high Mg-calcite or aragonite. However, aragonite is more abundant than calcite. Segmented sponges possessing a high-Mg calcite skeleton appear in the Middle Triassic for the first time and probably range up to the end of the Cretaceous. Rigid skeleton of Paleozoic, and most Mesozoic and younger genera are composed of aragonite.
Six types of rigid skeleton microstructure have been identified (spaerolitic, orthogonal, clinogonal, irregular, lamellar and microgranular). The lamellar type, whose primary nature was doubted by some workers, is described in detail from the Triassic genus Celyphia.
Irregular and sphaerolitic types are abundant in aragonitic sphinctozoans. Microgranular microstructure is typical of high-Mg calcite genera.
Relative values of various morphological and structural features in systematics are discussed in chapter 5. Structural features are used for higher systematic categories. The segmented sponges are classified, using a partly new system.
The main groups of segmented sponges are defined in chapter 6 and an alphabetic list of all families and genera is given. The following orders of segmented sponges are recognized. These belong either to the Calcispongia or Demospongea:
Sphaerocoelida: Calcispongea
Verticillitida: Demospongea (Ceractinomorpha)
Permosphincta: Demospongea (Ceractinomorpha), Calcispongea? (most genera of segmented sponges)
Hadromerida? (pars): Demospongea (Tetractinomorpha)
Guadalupida: Demospongea (Sclerospongea)
Because of the lack of a spicular skeleton, the systematic position of most genera of segmented sponges with a rigid skeleton composed of high-Mg calcite is uncertain. Chapter 7 includes the systematic description of sponges included in the orders listed above. Most Permian and Triassic genera are discussed in detail. Definition of some families and genera are revised. In addition to description of taxa, geographic distributions and stratigraphic ranges are given. The following families and genera including numerous species, are described as new:
Family Alpinothalamiidae n.fam.
Family Colospongiidae n.fam.
Family Cribrothalamiidae n.fam.
Family Palermocoeliidae n.fam.
Alpinothalamia n.g.
Cinnabaria n.g.
Cribrothalamia n.g.
Diecithalamia n.g.
Fania n.g.
Jablonskyia n.g.
Leinia n.g.
Lemonea n.g.
Nevadathalamia n.g.
Russospongia n.g.
Tolminothalamia n.g.
Uvothalamia n.g.
Zanklithalamia n.g.
Chapter 8 treats the occurrence and the frequency of segmented sponges through geologic time. Several crises in evolution of the segmented sponges can be recognized. The most important ones were at the Ordovizian / Silurian boundary, in the Lower Permian, at the Permian / Triassic boundary, Carnian / Norian boundary, Triassic / Jurassic boundary and at the Cretaceous / Tertiary boundary.
The paleoecology of segmented sponges and their role as frame builders within reefs are discussed in chapter 9. During early Paleozoic time segmented sponges lived in shelf area. Since the Lower Permian, especially in the Middle and Upper Permian and in the Triassic, they lived in reef biotopes. Everywhere in the world the Liassic segmented sponges (Stylothalamids) are found in bedded limestones. During the Cretaceous and later times the segmented sponges are also found in reef biotopes. The paleobiology of segmented sponges is discussed in chapter 10.
Possible phylogeny and relationships of different groups of segmented sponges are treated in chapter 11.
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