Acropora echinata (Dana, 1846)

Bridge, Tom C. L., Cowman, Peter F., Quaưrini, Andrea M., Bonito, Victor E., Frederic, Harii, Head, Catherine E. I., Hung, Julia Y., Halafihi, Tuikolongahau, Rongo, Teina & Baird, Andrew H., 2024, A tenuis relationship: traditional taxonomy obscures systematics and biogeography of the ‘ Acropora tenuis’ (ºcleractinia: Acroporidae) species complex, Zoological Journal of the Linnean Society 202 (1), pp. 1-24 : 18

Acropora echinata (Dana, 1846)

Madrepora echinata Dana 1846: 464 * plate 36* fig. 1.

Acropora echinata (Dana) : Verrill 1902: 214.

Madrepora duroillei Milne Edwards and Haime 1860: 148 .

Specimens examined: NMNH-SI: USNM 275 * Madrepora echinata holotype * Fiji; MNHN 282a * Madrepora duroillei holotype * Fiji; MTQ: G28406* G28460* G28461* G28409* G28458* G56982* G80268 GBR; G78007 Papua New Guinea; G60537* G60571* G80259 Coral Sea; G78322* * G80278 Fiji.

Remarks: Dana’s description of A.echinata is clearly based on USNM 275 ( Fig. 4F )* designated as the lectotype by Wallace (1999). It is a large specimen (~ 50 cm in diameter) from Fiji * which matches Dana’s description of an arborescent corallum with branches that are ‘very neatly bristled with delicate branchlets’ that give it an ‘even cylindrical outline’* ‘smooth tubiform calices’ and a costate coenosteum. We sequenced two specimens from the type locality (G78322 and G80278) with characters that very closely match the lectotype. These specimens confirm the identity of A. echinata * but the morphology of specimens in our study* from the GBR* the Coral Sea and the Bismarck Sea* show considerable morphological variability. In particular* specimen G80259 from Marion Reef in the Coral Sea is more bushy than the lectotype and topotype specimens from Fiji * while G78007 from the Bismarck Sea has thicker* less dense branches. However* all specimens of A. echinata have terete incipient axial corallites with square walls* compared with the thicker* more rounded tubular walls of other bottlebrush species. The coenosteum of A. echinata is costate* whereas other bottlebrush species ossen have elaborate spinules [e.g. Acropora subglabra Brook * 1891 (G71541)]. Additional specimens in the collection of MTQ also possess all these characters* providing strong morphological support for their identification as A. echinata .

Madrepora duroillei Milne Edwards & Haime * 1860 from Fiji and Madrepora procumbens Brook * 1891 from the ‘South Seas’ were considered junior synonyms of A. echinata by Veron and Wallace (1984) and Wallace (1999). Milne Edwards and Haime (1860) note that M. duroillei is very similar to M. echinata . The M. duroillei holotype (MNHN Z282a) is described as having ‘echinated ribs’ by Milne Edwards and Haime (1860)* which presumably refers to the coenosteum* and is from the same type locality as A. echinata * supporting previous decisions that the species is a junior synonym of this species. However* the type of A. procumbens (NHM 1841.12.11.3) has more rounded corallite walls and spinules on the coenosteum* and therefore more closely resembles bottlebrush species from Clade V [e.g. A. subglabra G71541 and G71543] than those from Clade I. Consequently* although A. procumbens does not appear to be a junior synonym of A. echinata (Dana* 1846)* further research is required to determine its taxonomic status and phylogenetic affinities.

The A. echinata genome assembled from a specimen collected from the Ryukyu Islands (Shinzato et al. 2021) is reconstructed in our study in Clade VI (labelled clade IV by Shinzato et al. 2021)* deeply diverged (> 50 Mya; Shinzato et al. 2021) from A. echinata (Dana* 1846) sampled from the type locality* which we reconstruct in Clade I (concordant with Clade I in the study by Shinzato et al. 2021). Unfortunately* there is no voucher or field image associated with this genome* hence we cannot comment on any morphological differences between these species. However* it is possible that the Coral Triangle / north-west Pacific region supports another distinct species with morphological similarities to A. echinata . Consequently* we do not include any specimens from these regions as A. echinata * pending further study. Based on the specimens we examined here* the current geographical range of A. echinata extends from the type locality in Fiji west across the Coral Sea to the Great Barrier Reef and north to the Bismarck Sea (Supporting Information* Fig. S6).

Figures

Figure 4. Nominal species of Acropora identified in this study. A* B* Acropora kenti (Brook 1892) topotype GBR130/G80247* Myrmidon Reef* GBR. C* A. kenti lectotype NHM 1892.6.8.202* Thursday Island* Australia. D* E* Acropora echinata Dana* 1846 topotype FJ139/G78322* Viti Levu* Fiji. F* A. echinata lectotype USNM 275* Fiji. G* H* Acropora tenuis Dana* 1846 topotype FJ127/G78323* Viti Levu* Fiji. I* A. tenuis holotype USNM 259* Fiji.J* K* Acropora yongei Veron & Wallace* 1984 topotype GBR85/G78644* Lodestone Reef* GBR. L* A. yongei holotype G55079* Britomart Reef* GBR.A field image (less column)* skeletal image (middle column) and type specimen (right column) are shown for each species. M–V* specimens examined in this study that could not be assigned to nominal species: PN63 Acropora aff.striata* Ant Atoll* Micronesia (M* N); KM27/G71345 Acropora aff.echinata* Kimbe Bay* Papua New Guinea (O* P); 54-5921/RUMF-ZG-04792 Acropora akajimensis Veron* 1990 topotype specimen placed within Acropora sp(p). clade* Ryukyu Islands* Japan (Q* R); 54-6036/RUMF-ZG-04796 Acropora sp.* Ryukyu Islands* Japan (S* T); and BFC219 Acropora aff.tenuis ‘WIO’* Chagos* Indian Ocean (U* V).