Table 1 Identification criteria based on morphological characters used for distinguishing Acropora solitaryensis and A. divaricata.
References | Acropora divaricata | Acropora solitaryensis | ||
|---|---|---|---|---|
Veron and Wallace, 198423 | Wallace, 199922 | Veron and Wallace, 198423 | Wallace, 199922 | |
Corallum | ||||
 Branching pattern | Thick tables or bowl/bracket-shaped with central or lateral attachment, 1 m or more in height and diameter | Open caespito-corymbose with tapering branches | A. divaricata-like branching pattern, basal branches fused into a perforated or solid plate | Tabulate, table tops formed by anastomosing and upwardly curving, tapering branches |
 Branch size | Caespitose branching, distal branches 6–12 mm diameter | Branches 5–15 mm in diameter, up to 70 mm |  | Branches 5–15 mm in diameter, up to 45 mm |
 Branch arrangement | Branching pattern and colony shape varying greatly | Curving and anastomosing to form a network within the colony |  | Anastomosing and upwardly curving |
 Growth type |  | Determinate |  | Determinate |
Corallites | ||||
 Axial corallites | Usually 2.3–3.0 mm diameter, with calices 0.8–1.1 mm diameter | Outer diameter 1.8–3.0 mm, inner diameter 0.7–1.1 mm | Up to 3 mm exsert, 3.4 mm diameter with calices 0.7–1.0 mm diameter | Outer diameter 1.6–3.4 mm, inner diameter 0.5–1.1 mm |
  Primary septa | Two cycles up to 1/2R and 1/4R, the latter frequently incomplete | Present up to 1/R | Usually in complete cycles of 1/2R | Present up to 1/2R |
  Secondary septa |  | Absent or some to all present to 1/4R | Usually incomplete to absent | Absent or a few just visible, up to 1/4R |
 Radial corallites | Change in shape and size along branches, from prominent on upper branchlets extending from 45° to 90°, tubular on branch tips, passing through tubo-nariform to nariform, then rounded to sub-immersed proximally | Evenly sized and spaced on branches, nariform, with large, open calices | Tubular appressed on branchlets, becoming immersed on basal branches. Circular to nariform, diameter 1.0–1.3 mm | Evenly sized and arranged, nariform or tubo-nariform, with large, open calices |
  Primary septa | Extremely variable septal development, some corallites with only rudimentary septa, others with two well-developed cycles | Present up to 1/2R with obvious directives | Septal development varies, both cycles may be present up to 2/3R | Present up to 1/3R |
  Secondary septa |  | Present up to 1/4R | Usually incomplete to absent | Absent or a few just visible, up to 1/4R |
 Distally radial corallites |  | Tubo-nariform; towards the base, appressed tubular, sometimes walls extended by prostrate development |  | Tubo-nariform; towards the base, appressed tubular, sometimes walls extended by rostrate development |
Coenosteum | ||||
 Texture | Consists of rows of laterally flattened or forked spinules, spongy between corallites | Reticulate | Usually the same on and between corallites | Reticulate |
 Radial corallites |  | Dense arrangement of laterally flattened or forked spinules | Covered with rows of fine spinules, may develop into distinct costae | Dense arrangement of laterally flattened or forked spinules |
 Intercorallite areas |  | Spinules less densely arranged |  | Spinules less densely arranged |
Other systematic information and remarks | ||||
 Similarity to other species | Have similar radial corallites and a coenosteum with A. clathrata but can differ by growth form. Acropora secale may be confused with A. divaricata but is readily distinguished by having radial corallites of two sizes, the larger having a tubular form. | Very similar to Acropora solitaryensis, distinguished mainly by growth form | Superficially does not resemble any other species. Closest affinities are with A. divaricata | Looks like a flattened form of A. divaricata, with branches sometimes forming a solid plate |
 Syntype information | – | Syntype of Acropora stoddarti Pilai & Scheer, 1976 is a flattened colony, growing on a wreck |  |  |
 Growth form variation | Wide range of skeletal variation within single biotopes, seldom develops well-defined, environment-related ecomorphs. One exception is sometimes found in coralla growing on soft substrates, or in turbid water where branchlets become flattened and the colony prostrate (viz. A. stoddarti Pillai & Scheer, 1976). In extreme cases, branchlets become fused into thin plates. Some skeletal developments (e.g. various types of corallite wall thickening and the development of naked branchlets) appear to be commonly associated with particular populations rather than particular environments. |  |  | Varies greatly in thickness of branches, can appear quite delicate or very sturdy |
 Distribution |  |  | Abundant at specific locations but rare elsewhere. Divisible into five geographic subspecies, widely separated spatially and environmentally | Very common species in the Indian Ocean, Indonesia, and South China Sea. Surprisingly rare on the Great Barrier Reef proper as reported in Veron & Wallace, 1984 |
 Geographic subspecies |  |  | Indicates five geographic subspecies, needing experimental verification to confirm as a single species unit |  |
