Paragoniastrea
Huang, Benzoni, and Budd, 2014
The name alludes to its superficial similarities with Goniastrea, particularly its well-developed paliform lobes, but is distinguished from the latter based on molecular and subcorallite characteristics.
Type Species
Prionastræa australensis Milne Edwards and Haime, 1857, p. 520; Original Designation Huang et al., 2014
Type Specimen: Holotype; MNHN IK-2010-409; Verified; Dry Preserved
Type Locality: Australia
Classification
Diagnosis
Colonial; mostly intracalicular budding, with some degree of extracalicular budding in monocentric species. Corallites monomorphic; discrete (1–3 centers) or uniserial; monticules absent. Walls generally fused, but may also occur as double walls. Coenosteum, if present, limited and costate. Calice width medium (4–15 mm), with medium relief (3–6 mm). Costosepta may be confluent. Septa in 3 cycles (24–36 septa). Free septa present but irregular. Septa spaced 6–11 septa per 5 mm. Costosepta generally unequal in relative thickness. Columellae trabecular and spongy (> 3 threads), < 1/4 of calice width, and continuous among adjacent corallites. Paliform (uniaxial) lobes well developed. Epitheca well developed. Endotheca low-moderate (tabular). Tooth base at mid-calice circular. Tooth tip at mid-calice irregular; tip orientation perpendicular to septum. Tooth height medium (0.3–0.6 mm) and tooth spacing medium (0.3–1 mm), with > 6 teeth per septum. Granules scattered on septal face; irregular in shape. Interarea palisade. Walls formed by dominant paratheca and partial septotheca; abortive septa absent. Thickening deposits fibrous. Costa centre clusters weak; 0.3–0.6 mm between clusters; medial lines weak. Septum centre clusters weak; generally 0.3–0.5 mm between clusters, but may be closer in some septa; medial lines weak. Transverse crosses absent. Columella centres clustered.
Comparisons
Paragoniastrea is morphologically similar to Goniastrea and Favites, with members being classed in these genera prior to the present revision. Due in part to several symplesiomorphies shared between Paragoniastrea and members of subclade A on the morphological phylogeny (e.g. well-developed paliform lobes and absence of transverse crosses), no unambiguous synapomorphies could be inferred. A transition from moderate (< corallite diameter) to limited coenosteum amount occurred on the Paragoniastrea branch, but the walls became fused in P. australensis and P. deformis. Wall fusion also independently evolved within subclade A (in Merulina, Scapophyllia and most Goniastrea spp.), Coelastrea aspera and Oulophyllia crispa. Paragoniastrea can be distinguished macromorphologically from Goniastrea in having higher calice relief (3–6 mm), spongy columellae (> 3 threads), and internal lobes that are only uniaxial (paliform). For subcorallite features, Paragoniastrea has greater septal tooth height (0.3–0.6 mm) and spacing (0.3–1 mm), walls formed by dominant paratheca without abortive septa, and wider spacing between costa and septum centre clusters (0.3–0.6 mm). Paragoniastrea has fewer morphological characters separating it from Favites—smaller number of septal cycles (24–36 septa), less abundant endotheca, weaker costa centre clusters and no transverse septal crosses (see fig. 13 in Huang et al. 2014). The three species in Paragoniastrea can be distinguished based on their macromorphology. Paragoniastrea australensis is the only species with uniserial corallites and walls that are always fused between adjacent valleys (Milne Edwards and Haime 1857), while P. deformis possesses more irregular skeletal elements and the 'groove' and tubercle' formation, as in the holotype (Veron 1990). Paragoniastrea russelli exhibits varying degrees of wall fusion and coenosteum development, and unlike its congenerics, usually has considerable size differentiation between costoseptal cycles, the first being greatly thickened and exsert (Wells 1954). The unidentified Paragoniastrea sp. from Japan has affinities to both P. deformis and P. russelli but has more regular corallite features. It may be a new species, but its boundaries are in need of clarification with more extensive sampling.
Remarks
Paragoniastrea was established based on a combination of molecular and morphological evidence from Huang et al. (2011, 2014a, b). Of its three constituent species, P. deformis is the first to be examined phylogenetically. Based on mitochondrial cytochrome oxidase I and cytochrome b genes, Fukami et al. (2008) recovered it as the deepest branching lineage within subclade A (sensu Budd and Stolarski 2011), the clade containing Merulina, Goniastrea and Scapophyllia. It is clearly distinct from two of the three clades of Goniastrea as defined here. Later, a suite of five genes, including the three used in this study, showed that P. australensis and P. russelli are outside subclade A (Huang et al. 2011). The present study is the first to place all three species of Paragoniastrea in the same context, with data pointing to a well-supported monophyly that defines this new genus. Based on the histone H3 marker, Paragoniastrea is sister to the least inclusive clade comprising Merulina and Dipsastraea, but this relationship is not supported. Together, they form a relatively well-supported clade that excludes Echinopora and Paramontastraea. With the latter as outgroups, the nuclear ITS recovers Paragoniastrea as sister to subclade A with moderate support, while mitochondrial IGR groups the new genus with the clade containing Goniastrea retiformis, G. minuta and G. stelligera. However, we note above that the extremely long branch produced by the IGR data suggests that this grouping may not be reliable. Taken together, Paragoniastrea is distinct from all other merulinid genera but is likely to be the sister group to subclade A as suggested by the ITS tree. Paragoniastrea and subclade A could also be a paraphyly with respect to the least inclusive clade comprising Caulastraea and Dipsastraea, though this has received much less support from histone H3. Paragoniastrea is widely distributed on reefs of the Indo-Pacific, recorded as far east as the Pitcairn Islands in the southern hemisphere (Glynn et al. 2007) and Marshall Islands in the northern hemisphere (Wells 1954; Veron et al. 2009, 2011).
Distribution
- Indian Ocean; Recent
- Western Pacific; Recent
- Central Pacific; Recent
This page has been in preparation since 12-Jun-2014 10:19
This version was contributed by Danwei Huang on 14-Jun-2014 04:47.
Page authors are: 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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