Baron-Szabo, R.C. & S.D. Cairns. (2017). Part F, Revised, Volume 2, Chapter 11: Systematic descriptions of the Scleractinia Family Micrabaciidae. Treatise Online, Paleontological Institute, University of Kansas, USA. 98: 1-8.

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10.17161/to.v0i0.6671 [view]

Baron-Szabo, R.C. & S.D. Cairns

2017

98: 1-8

Publication

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The Micrabaciidae is one of the smallest and least diverse scleractinian families, consisting of the five genera: Micrabacia milne eDwaRDs & haime (20 fossil species), Leptopenus moseley (four extant species), Letepsammia yaBe & eguChi (four extant species), Rhombopsammia owens (two extant species), and Stephanophyllia m i C helin (three extant and ten fossil species). Thus, nearly 40 valid species pertain to this family ( C ai R ns , 1989, p. 13–24; B a Ron - s za B o , 2002, p. 130–131; 2008, p. 147–153), most of which (30) are known exclusively as fossils. Only the two genera, Leptopenus moseley, 1881 and Rhombopsammia owens, 1986 are as yet known exclusively from the Holocene. The monophyly of the family is supported by macromorphological, microstructural, and molecular evidence. The macromorphological evidence includes a unique pattern of septal and costal insertion, alternating septa and costae, and the frequent presence of a marginal shelf. These characters are best illustrated and discussed by CaiRns (1989), who also supplied a key to four (those with living species) of the five genera. The unique pattern of septal insertion, once thought to be a repeated bifurcation of the third cycle septa (CaiRns, 1989), was shown by Janiszewska, JaRoszewiCz, and stolaRski (2013) to be accomplished by unequal-length invaginations of the wall between septa at the peripheral edge of the calice, and thus could not originate from bifurcation. Nonetheless, the result in adult corals resembles bifurca- tion and was even called pseudo-bifurcate by Janiszewska, JaRoszewiCz, and stolaRski (2013). The unique microstructural skeletal composition was first described by Janiszewska and others (2011) and later elaborated by J aniszewska and others (2015). The molecular monophyly, based exclusively on the mitochondrial gene CO1, was discussed by kitahaRa and others (2010), and based on four genes, both mitochondrial and nuclear, by s tola R ski and others (2011). According to kitahaRa and others (2010) and stolaRski and others (2011), the Micrabaciidae, along with the Gardineriidae, form a deeply diverging basal clade, equivalent to the robust and complex clades that encompass all other Scleractinia. This chapter gives an overview of the taxonomy, stratigraphy, and geography of the genera currently included in the family Micrabaciidae. The diagnosis of the family is followed by the description of its nominate genus, and then descriptions of the other genera in alphabetical order. Table 1 (p. 7) provides a synopsis of micrabaciid genera, including key characteristics and stratigraphic ranges

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