Orbicella
Dana, 1846, p. 205
Type Species
Madrepora annularis Ellis and Solander, 1786, p. 169, pl. 53, figs. 1,2; Subsequent Designation Vaughan, 1918, p. 85
Type Specimen: Holotype; GLAHM 104008; Verified; Dry Preserved
Type Locality: 'Antilles' (Weil and Knowlton, 1994, p. 155)
Classification
Diagnosis
Colonial, with extracalicular budding only. Corallites monomorphic and discrete (1–3 centers); monticules absent. Coenosteum costate, moderate amount (< corallite diameter). Calice width small (< 4 mm), with low relief (< 3 mm). Costosepta not confluent. Septa in 3 cycles (24–36 septa). Free septa regular. Septa spaced > 11 septa per 5 mm. Costosepta equal in relative thickness. Columellae trabecular but compact (1–3 threads), ≥ 1/4 of calice width, and discontinuous among adjacent corallites. Paliform (uniaxial) lobes absent. Epitheca well developed and endotheca low-moderate (tabular). Tooth base at mid-calice circular. Tooth tip at mid-calice irregular; tip orientation multiaxial. Tooth height low (< 0.3 mm) and tooth spacing narrow (< 0.3 mm), with > 6 teeth per septum. Granules scattered on septal face; irregular in shape. Interarea smooth. Walls formed by dominant septotheca and partial paratheca; abortive septa absent. Thickening deposits fibrous. Costa center clusters weak; 0.3–0.6 mm between clusters; medial lines weak. Septum center clusters weak; < 0.3 mm between clusters; medial lines weak. Transverse crosses absent. Columella centers clustered.
Description
'Cells nearly circular, more or less prominent, not subdividing by growth, or rarely so; stars with distinct limits formed by the coalescence laterally of the lamellae, and therefore cells appearing tubular, and separated by interstices' (Dana, 1846: 205)
Comparisons
The present Orbicella members form a very well-supported clade, and a sister-clade relationship with Cyphastrea is recovered but not supported. It is remarkable that these two genera are recovered as sister taxa on the morphology tree, particularly because they differ in up to four macromorphological characters, two of which being the only synapomorphies inferred for Orbicella—equal costosepta thickness and large columellae. Costate coenosteum and the lack of paliform lobes also distinguish Orbicella from Cyphastrea, which has spinose coenosteum and weak or moderate development of paliform lobes. However, their affinity to each other may be expected in the context of subcorallite characters, which show that they share all but two features of irregular granule shape and partial paratheca in Orbicella, rather than strong, pointed granules and no paratheca at all in Cyphastrea.
Remarks
The three Caribbean members of this genus used to be known as the Montastraea annularis complex (Knowlton et al., 1992; Weil and Knowlton, 1994), and were the focus of extensive research aimed at describing morphological, genetic, reproductive and physiological variation among them (Knowlton et al., 1992; van Veghel and Bak, 1993, 1994; van Veghel, 1994; van Veghel and Kahmann, 1994; Weil and Knowlton, 1994; van Veghel and Bosscher, 1995; van Veghel, Cleary and Bak, 1996; Knowlton et al., 1997; Lopez and Knowlton, 1997; Szmant et al., 1997; Lopez et al., 1999; Medina, Weil and Szmant, 1999; Manica and Carter, 2000; Knowlton and Budd, 2001; Fukami et al., 2004; Levitan et al., 2004, 2011, Fukami and Knowlton, 2005). Although currently restricted to the Caribbean showing no geographic overlap with any other living Merulinidae genus, the subgenus Orbicella described by Dana, 1846: 205 within Astrea also included numerous Indo-Pacific species such as Cyphastrea microphthalma, Astrea curta and Oulastrea crispata (incertae sedis). The subsequent designation of Madrepora annularis Ellis and Solander, 1786: 169 as type species by Vaughan, 1918: 85 also did not constrain its geographic range, as Plesiastrea versipora, Orbicella gravieri (synonym of P. versipora; Veron et al., 1977: 150) and Astrea curta were retained. Orbicella was finally synonymized by Vaughan and Wells, 1943: 173 as Montastraea de Blainville. Molecular data have generally placed the Orbicella clade as sister to Cyphastrea with good support (Fukami et al., 2004; Huang et al., 2011; Huang, 2012; Arrigoni et al., 2012; but see Fukami et al., 2008).
Distribution
This page has been in preparation since 20-Jul-2010 03:56
This version was contributed by Danwei Huang on 05-Feb-2014 22:59.
Page authors are: Ann Budd Danwei Huang. Please contact the editor if you would like to contribute to the diagnosis of this taxon.
The editor is: Ann Budd
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