Astrea, LAMARCK, 1801: 371

Huang, Danwei, Benzoni, Francesca, Fukami, Hironobu, Knowlton, Nancy, Smith, Nathan D. & Budd, Ann F., 2014, Taxonomic classification of the reef coral families Merulinidae, Montastraeidae, and Diploastraeidae (Cnidaria: Anthozoa: Scleractinia), Zoological Journal of the Linnean Society 171 (2), pp. 277-355 : 296-298

GENUS ASTREA LAMARCK, 1801: 371 ( FIG. 4 )

Type species

Madrepora rotulosa Ellis & Solander, 1786: 166 , pl. 55: figs 1–3 (non Astrea rotulosa Lamarck, 1801: 371 ; see Article 70.3.1 of the Code); original designation, Lamarck, 1801: 371.

Original description

‘Polypier pierreux, crustacé, en masse glomérulée ou en expansion lobée subfoliacée, ayant sa surface supérieure parsemée d’étoiles lamelleuses et sessiles.’ ( Lamarck, 1801: 371).

Subsequent descriptions

Lamarck, 1816: 257, 258; Lamouroux, 1821: 57; de Blainville, 1830: 332; Quoy & Gaimard, 1833: 199, 200; de Blainville, 1834: 366, 367; Ehrenberg, 1834: 319; Lamarck, 1836: 401–404; Dana, 1846: 200–205; Milne Edwards & Haime, 1848a, vol. 27: 494; Milne Edwards & Haime, 1849b, vol. 12: 97; d’Orbigny, 1851: 170; Milne Edwards & Haime, 1857, vol. 2: 505; Dana, 1859: 22; Quenstedt, 1885: 1000; Quelch, 1886: 96; Gardiner, 1899: 747, 748.

Diagnosis (apomorphies in italics)

Colonial, with extracalicular budding; no intracalicular budding. Corallites monomorphic and discrete (one to three centres); monticules absent. Coenosteum costate, moderate amount (<corallite diameter). Calice width medium (4–15 mm), with medium relief (3–6 mm). Costosepta not confluent. Septa in three cycles (24– 36 septa). Free septa present, may be regular or irregular. Septa spaced six to 11 septa per 5 mm. Costosepta unequal in relative thickness. Columellae trabecular and spongy (> three threads), <1/4 of calice width. Paliform (uniaxial) lobes well developed. Epitheca well developed and endotheca low−moderate (tabular) ( Fig. 4A, D, G ).

Tooth base at midcalice circular. Tooth tip at midcalice irregular; tip orientation perpendicular to septum. Tooth height low to medium (≤ 0.6 mm) and tooth spacing medium (0.3–1 mm), with> six teeth per septum. Granules scattered on septal face; irregular in shape. Interarea palisade ( Fig. 4B, E, H ).

Walls formed by dominant paratheca and partial septotheca; abortive septa weak. Thickening deposits fibrous. Costa centre clusters weak; 0.3–0.6 mm between clusters; medial lines weak. Septum centre clusters weak; 0.3–0.5 mm between clusters; medial lines weak. Transverse crosses absent. Columella centres clustered ( Fig. 4C, F, I ).

Species included

1. Astrea rotulosa ( Ellis & Solander, 1786: 166, pl. 55: figs 1–3); holotype: GLAHM 104014 (dry specimen; Fig. 4A ); type locality: unknown; phylogenetic data: none .

2. Astrea annuligera Milne Edwards & Haime, 1849b, vol. 12: 103; holotype: MNHN IK-2010-699 (dry specimen; Fig. 4G ); type locality: Australia; phylogenetic data: morphology only .

3. Astrea curta Dana, 1846: 209 , pl. 10: fig. 3a–c; syntypes: USNM 14 ( Fig. 4D–F ), 22 (two dry specimens); type locality: Fiji; phylogenetic data: molecular and morphology .

4. Astrea devantieri ( Veron, 2000, vol. 3: 228, figs 1, 2) (see also Veron, 2002: 167, figs 303–305; ICZN, 2011: 165); lectotype (designated herein): MTQ G55847 (dry specimen); type locality: Hawlaf, Socotra, Gulf of Aden, 3–12 m depth; phylogenetic data: molecular and partial morphology.

Taxonomic remarks

Astrea Lamarck, 1801: 371 , is the oldest genus in Merulinidae , and was first established as part of a class of animals possessing polyps, Polypes Lamarck, 1801: 357. Sixteen of the genera were in the subdivision described as ‘Polypier solide, entièrement pierreux et calcaire’ ( Lamarck, 1801: 369) – having polyps that are solid, completely stony and calcareous – resulting in the redistribution of species of the only stony coral genus prior to 1801, Madrepora Linnaeus, 1758: 793 (see Vaughan & Wells, 1943: 2, 3). Subsequent works, including Lamarck (1816: 257), de Blainville (1830: 332), and Dana (1846: 200), attributed as many as 61 species to Astrea before the establishment of additional genera by Milne Edwards & Haime (1848a, vol. 27: 494– 496). Astrea was then split into several genera, and also assigned Astrea argus Lamarck, 1816: 259 as the type species ( Milne Edwards & Haime, 1848a, vol. 27: 494), instead of Astrea rotulosa ( Ellis & Solander, 1786: 166) . Curiously, ‘ Astrea rotulosa et ananas, Lamarck’ was ascribed to be the type of Parastrea Milne Edwards & Haime, 1848a, vol. 27: 495, which is a synonym of Dichocoenia Milne Edwards & Haime, 1848a, vol. 27: 469 (see Gregory, 1895: 270).

The genus was synonymized by Matthai (1914: 84, 115), as Favia after recognizing types of both Madrepora rotulosa Ellis & Solander, 1786: 166 , and Astrea rotulosa Lamarck, 1801: 371 , to be part of Favia . Matthai (1914: 115) also compared Ellis & Solander’s (1786: 166) type of Madrepora rotulosa with Orbicella annularis , a Caribbean species. This specimen, not Astrea rotulosa Lamarck, 1801: 371 , or Favia rotulosa Ehrenberg, 1834: 319 , is clearly the original designated type of Astrea . However, this specimen bears the closest resemblance to Plesiastrea devantieri Veron, 2000 , vol. 3: 228, especially given their well-developed paliform lobes that are absent amongst the Orbicella species defined in this study. We thus revive this genus to include Madrepora rotulosa , Plesiastrea devantieri , as well as species that have been found to be closely related genetically and morphologically.

Astrea is widely distributed on reefs of the Indo- Pacific, recorded throughout most of French Polynesia and the Pitcairn Islands in the Southern Hemisphere ( Glynn et al., 2007), but absent eastwards from Hawai’i in the north.

Morphological remarks

Astrea rotulosa has not been placed on the molecular phylogeny, but it is most similar to Astrea devantieri . Each macromorphological character examined is the same state for both species, except for the more compact columellae in the type specimen of the former. Spongy columellae can however be found in Favia rotulosa specimens studied by Ehrenberg (1834: 319; ZMB Cni 739II), and Wijsman-Best (1974: 258, pl. 4, fig. 4; ZMA Coel. 8888), collected from the Red Sea and Indonesia, respectively. Consequently, we hypothesize that Astrea devantieri , thus far recorded only from Socotra (type locality), Madagascar, and Mayotte ( Veron, 2002; Benzoni et al., 2011), is a sister species to Astrea rotulosa . Although we have limited data to place all Astrea spp. on the tree concomitantly, we infer that Astrea annuligera Milne Edwards & Haime, 1849b, vol. 12: 103, and Astrea curta Dana, 1846: 209 , are closely related based on morphology.

As this genus is represented only by Astrea curta on the molecular tree, no synapomorphies are diagnosed – absence of intracalicular budding and weak abortive septa are autapomorphies. On the morphological phylogeny, however, these features are synapomorphies.

Goniastrea australensis has been recovered as the sister taxon to Astrea curta + Favites russelli in one instance ( Huang et al., 2011; but see Arrigoni et al., 2012). Morphologically, Goniastrea australensis is very distinct from Astrea as it lacks extracalicular budding, has uniserial corallites, fused walls, confluent costosepta, evenly thick costosepta, and narrow distance between septum centre clusters (<0.3 mm). Most of these characters, except uniserial corallites and confluent costosepta, and many others, also separate the Goniastrea proper from this genus.

Favites russelli is the sister taxon to Astrea on the molecular tree, but it buds intracalicularly and does not have abortive septa. Therefore it cannot be considered in the latter genus.

Figures

Figure 4. Astrea Lamarck, 1801, has discrete corallites that bud extracalicularly, medium-size (4–15 mm) and mediumrelief (3–6 mm) calices, septa in three cycles (24–36 septa), well-developed paliform (uniaxial) lobes, and spongy columellae. Septal teeth with low−medium height (≤ 0.6 mm) and medium spacing (0.3–1 mm). Walls formed by dominant paratheca, partial septotheca, and weak abortive septa. A, Astrea rotulosa (Ellis & Solander, 1786), type species of Astrea; macromorphology, holotype GLAHM 104014, unknown locality (photo by KG Johnson). B–F, Astrea curta Dana, 1846; micromorphology (scanning electron microscopy; B) and microstructure (transverse thin section; C), hypotype MTQ G61882, Orpheus Island, Australia; macromorphology (D), micromorphology (E), and microstructure (F), syntype USNM 14, Fiji. G–I, Astrea annuligera Milne Edwards & Haime, 1849b; macromorphology, holotype MNHN IK-2010-699, Australia (G); micromorphology (H) and microstructure (I), hypotype RMNH 10718, Heron Island, Australia.