ZMB 299, lectotype (herein designated), Red Sea, leg. Hemprich, Ehrenberg; ZMB 298, two paralectotypes, same data as holotype; ZMB 300, same data as holotype.

RMNH Coel. 8890, Gulf of Aqaba, Red Sea, 1.5 km N of Saudi Arabian border, 50–70 cm, 10–20 m from coast, 15 February 1972, coll. H. Schumacher, det. J. Verseveldt, one specimen and two microscope slides; RMNH Coel. 8891, Gulf of Aqaba, Red Sea, 1.5 km N of Saudi Arabian border, 80 cm, 18 February 1972, coll. H. Schumacher, det. J. Verseveldt, one specimen and two microscope slides; RMNH Coel. 8892, Marsa el Muqeibla (= Makbala), Gulf of Aqaba, Red Sea, from reef wall, 6 January 1968, coll. Hebrew University, Jerusalem - Smithsonian Red Sea project 63/SLR 1147, det. J. Verseveldt, one specimen and 3 microscope slides; RMNH Coel. 8944, Marsa abu Zabad, Gulf of Aqaba, Red Sea, 15 September 1967, coll. Hebrew University, Jerusalem - Smithsonian Red Sea project, det. J. Verseveldt, one specimen and five microscope slides; RMNH Coel. 8951, Marsa el Maqeilba, Gulf of Aqaba, Red Sea, 6 January 1968, coll. Hebrew University, Jerusalem - Smithsonian Red Sea project, det. J. Verseveldt, one specimen and four microscope slides; ZMTAU Co 25287, Red Sea, Gulf of Aqaba, Nakeb Shahin, 25 m, coll. Y. Benayahu, 29 November 1981; ZMTAU Co 25309, Red Sea, southern tip of Sinai Peninsula, Sharm El Sheikh, 25 m, coll. Y. Benayahu, 30 November 1981; ZMTAU Co 25378, Red Sea, Gulf of Aqaba, Nakeb Shahin, 18-24 m, coll. Y. Benayahu, 5 November 1981; ZMTAU Co 25419, Red Sea, Gulf of Aqaba, Taba, 1 m, coll. Y. Benayahu, 30 July 1984; ZMTAU Co 26119, Red Sea, North, Tawila Island, 6 m, coll. Y. Benayahu, 24 September 1989; ZMTAU Co 31609, Red Sea, Eritrea, Dahlak Archipelago, Dahlak Island, channel in front of Lul hotel, coll. M. Schleyer, 12 February 1998; ZMTAU Co 31610, Red Sea, Eritrea Dahlak Archipelago, Intere Island, 15°38.504'N, 39°53.580'E, 12.5 m, coll. M. Schleyer, 3 May 1997; ZMTAU Co 32947, Red Sea, Eritrea, Dahlak Archipelago, between Nocra Island and Dahlak Island, southern entrance to the channel, 15°41.60'N, 39°56.40'E, 2–3 m, coll. Y. Benayahu, 15 February 2005; ZMTAU Co 32961, Red Sea, Eritrea, Dahlak Archipelago, Shumma Island, 15°32.00'N, 40°00.00'E, 8–12 m, coll. Y. Benayahu, 16 February 2005; ZMTAU Co 33104, Israel, Gulf of Aqaba, Eilat, Marine laboratory, reef off the Inter University Institute for Marine Sciences, 50 m, coll. S. Einbinder, 8 June 2004; ZMTAU Co 35301, Israel, Gulf of Aqaba, Eilat, reef off the Inter University Institute for Marine Sciences, 14 m, coll. Y. Benayahu, 19 January 2011; Sinularia compressa material: ZMTAU 34140, ZMTAU 34142, and ZMTAU 34150 used by McFadden et al. (2011).

The lectotype is 14.5 cm high and 9 cm wide (Figure 2A). The primary lobes give off short finger-like lobules up to 1 cm long. The polyp openings are visible as small pits.

Sclerites. Polyps without sclerites. The surface layer of the lobules has clubs with a distinct central wart, the smallest are 0.07 mm long, most are around 0.10 mm, but some reach even a length of 0.15 mm (Figure 3A). Furthermore, the surface layer of the lobules has spindles, up to 0.25 mm long, with simple tubercles (Figure 3B). The sclerites of the surface layer of the base of the colony resemble those of the surface layer of the lobules, but the clubs are much shorter, only up to 0.10 mm long, with wider handles. The spindles are also wider and shorter than those of the top of the colony, up to 0.15 mm long (Figure 4). The interior of the colony has unbranched spindles. In the lobules the spindles are up to 2 mm long (Figure 5A), featuring simple or complex tubercles (Figure 5B). In the base of the colony they are up to 3 mm long (Figure 5C), many with more complex tubercles (Figure 5D).

Colour. The alcohol-preserved specimen is light brown.

The two paralectotypes ZMB 298 are smaller than the lectotype (Figure 2B) but the sclerites are similar (Figure 6). Paralectotype ZMB 300 is not a Sinularia, but a Cladiella specimen, as proven by its colony shape and typical suite of figure-eight and dumbbell sclerites (Figures 2C, 7–8).

Notably the Red Sea Sinularia polydactyla colonies can be much larger than the lectotypes and have longer lobules (Figure 2F, ZMTAU 31610).

Sinularia compressa Tixier-Durivault, 1945 exhibits close similarity to Sinularia polydactyla. It differs in having clubs in the surface layer of the lobes with more slender handle and spinier head. Sinularia compressa specimens ZMTAU 34140, 34142, and 34150, all from the Red Sea (Figure 2G) feature similar sclerites (Figures 9–11) despite differences in their colony shape.

Finally, we re-examined the type of Sinularia candidula Verseveldt & Benayahu, 1983, RMNH Coel. 11837, also depicting its sclerites (Figures 12–14). There were no noticeable differences between that species and specimens identified as Sinularia polydactyla, and therefore we synonymized Sinularia candidula also with Sinularia polydactyla.