Figs. 3B–C, 4, 5
Sympodium caeruleum Ehrenberg 1834: 61
Sympodium caeruleum Ehrenberg, 1834; Dana, 1846: 609; Hickson 1931: 174; Gohar 1940: 107–108, pl. VIII; Benayahu 1990: 118 (listed only); Reinicke 1995: 56–57, figs. 1, 12; Reinicke 1997: 23, figs 7a–b, Plate 9, 13; McFadden et al. 2011 (listed only); Haverkort-Yeh et al. 2013 (listed only); McFadden et al. 2019 (listed only).
Sympodium coeruleum: Milne Edwards & Haime 1857: 111; Gray, 1869: 120; Wright & Studer, 1889: 271 (listed only).
S. coeruleum: Kükenthal 1904: 39–41, plate 4, fig. 3; pl. 5, figs. 13, 14; Kükenthal 1913: 2 (listed only); Kükenthal 1916: 456.
? Sympodium cöruleum: Klunzinger 1877: 42–43, Plate 3, Fig. 5.
Not Sympodium caeruleum: May 1899: 51–52; Thomson & Henderson: 1906: 408; Thomson & Mackinnon, 1910: 168; Thomson & Dean 1931: 21; Roxas 1933: 107, pl. 3 fig. 4; Macfadyen 1936: 23; Tixier-Durivault 1966: 371–372, fig. 334; Verseveldt 1973: 168–169; Utinomi: 1977: 7–8, plate II, fig. 5; Benayahu 1993: 6 (listed only); Malyutin 1992: 2 (listed only): Janes 2013: 198 (listed only); McFadden et al. 2014a: Table 1.
Material examined. Syntypes: Egypt. ZMB Cni 240 (several colonies), northern Red Sea, Gulf of Suez, Sinai, At-Tur, coll. H. H. R. Hartmeyer. Additional material: Egypt. ZMH C 3245, same details; SMNHTAU_ Co _ 9897, northern Red Sea Gulf of Suez, Abu Durbah (28° 28’ 25”N, 33° 19’ 51”E), 1 October 1972, coll. L. Fishelson; SMNHTAU_ Co _ 9898, same details; SMNHTAU_ Co _ 25585, same details; SMNHTAU_ Co _ 25397, northern Red Sea, southern tip of Sinai Peninsula, 2–5 m, 8 November 1981, coll. Y. Benayahu; SMNHTAU_ Co _ 25641, northern Red Sea, southern tip of Sinai Peninsula, Shaab al Utaf (27°45’ 23.6”N, 34°10’10.4”E), 3 m, 15 August 1987, coll. Y. Benayahu; SMNHTAU_ Co _ 26022, northern Red Sea, southern tip of Sinai, 27 March 1987, coll. Y. Benayahu; SMNHTAU_ Co _ 26024, northern Red Sea, Straits of Tiran, 18 m, 27 March 1988, coll. Y. Benayahu; SMNHTAU_ Co _ 26031, northern Red Sea, Gulf of Suez, Shag Rock (27°47’00.0”N 33°53’00.0”E), 25 m, 7 October 1987, coll. Y. Benayahu; SMNHTAU_ Co _ 26032, northern Red Sea, Gulf of Suez, Shag Rock (27°47’00.0”N 33°53’00.0”E), 8 October 1987, coll. Y. Benayahu; SMNHTAU_ Co _ 26033, northern Red Sea, southern tip of Sinai Peninsula, Shaab al Utaf (27°45’23.6”N, 34°10’10.4”E), 10 m, 5 October 1988, Coll. Y. Benayahu; Israel. SMNHTAU_ Co _ 7953, northern Red Sea, Gulf of Aqaba, Eilat, 1 June 1971, coll. L. Fishelson; SMNHTAU_ Co _ 34184, northern Red Sea, Gulf of Aqaba, Eilat, Princess Coral Reef (29°29.77’N, 34°54.53’E), 22.9–24.4 m, 26 July 2007, coll. Y. Benayahu; SMNHTAU_ Co _ 34185, same details; SMNHTAU_ Co _ 34919, northern Red Sea, Gulf of Aqaba, Eilat, Oil Jetty (29.52993°N, 34.93535°E), 13 m, 30 November 2008, coll. D. Aharonovich; SMNHTAU_ Co _35020; northern Red Sea, Gulf of Aqaba, Eilat, the reef across the Interuniversity Institute for Marine Sciences, Israel (29°30′N, 034°55′E), 10–12m, 19 February 2008, coll. D. Aharonovich; SMNHTAU_ Co _35028, northern Red Sea, Gulf of Aqaba, Eilat, Oil Jetty (29.52993°N, 34.93535°E), 13 May 2008, 12 m, coll. D. Aharonovich; SMNHTAU_ Co _35030 same details; SMNHTAU_ Co _35032 same details; SMNHTAU_ Co _ 35044, northern Red Sea, Gulf of Aqaba, Eilat, Coral Beach Nature Reserve (29.50993°N, 34.92.39°E), 20 m, 18 January, 2011, coll. A. Halász; SMNHTAU_ Co _ 37045, northern Red Sea, Gulf of Aqaba, Eilat, Oil Jetty (29.52993°N, 34.93535°E), 10 m, 9 November 2011, coll. A. Halász; SMNHTAU_ Co _ 37046, northern Red Sea, Gulf of Aqaba, Eilat, Oil Jetty (29.52993°N, 34.93535°E), 15 m, 9 November 2011, coll. A. Halász; SMNHTAU_ Co _ 37047, northern Red Sea, Gulf of Aqaba, Eilat, Princess Coral Reef, (29°29.77’N, 34°54.53’E), 25 m, 8 November 2011, coll. A. Halász; SMNHTAU_ Co _ 37048, northern Red Sea, Gulf of Aqaba, Eilat, Oil Jetty (29.52993°N, 34.93535°E), 10 m, 9 November 2011, coll. A. Halász; SMNHTAU_ Co _ 37688, Northern Red Sea, Gulf of Aqaba, Eilat, Princess Coral Reef (29°29.77’N, 34°54.53’E), 5 m, 20 March 2018, coll. R. Liberman. Saudi Arabia. USNM1201982, Al Lith, Marmar Reef (19 o 50’N, 39 o 56’E), 5 m, April 2011, coll. R. Haverkort-Yeh; USNM1201969, Dora Reef (19 o 49’N, 39 o 53’E), 6 m, April 2011, coll. R. Haverkort-Yeh; UF 9544, Yanbu, Shi’b Sufflami (23.543467°N, 38.22791°7E), 4 March 2014, coll. G. Paulay; UF 14223, Jeddah (21.7127°N, 39.0803°E), 24.4 m, 26 October 2018, coll. C. McFadden.
Description. The syntypes, ZMB Cni 240, consist of several small encrusting membrane-like colonies firmly attached to an irregular calcareous fragment measuring approximately 10 x 6 cm (Fig. 4A). The largest colony is 2.5 x 2 cm and the others are smaller, approximately 1 cm 2. Certain parts of the colonies are extended into small crevices of the fragment. The membrane overgrowing the substrate is 1–1.5 mm thick. Some of the polyps are fully retracted while others are partly expanded (Fig. 4B). The polyp body is up to 10 mm long and the tentacles up to 5 mm long. The pinnules are arranged in 3 rows, with 5–8 pinnules in the outermost row. They are short, approximately 1 mm long and 0.5 mm wide, with almost no space between adjacent ones.
The sclerites of the syntypes are ellipsoid platelets, highly abundant throughout the colony, measuring 0.010 – 0.012 x 0.014 –0.017 mm in diameter (Fig. 5A). They are composed of calcite rods, uniform in diameter of ca. 0.001 mm; the tips of the rods are perpendicular to the surface of the sclerite, giving it a granular appearance (Fig. 5B).
Color. The ethanol-preserved syntypes are gray.
Variation. The morphological features of the sequenced colony (SMNHTAU_Co_ 34185) resemble those of the syntypes, and it similarly grows over a calcareous fragment by means of a thin spreading membrane. The pinnules are arranged in 2–3 rows, with 6–7 pinnules in the outermost one. Some pinnules are retracted, however the few expanded ones are up to 1 mm in length. Similarly, other Red Sea colonies that were sequenced (USNM1201982 and USNM 1201969) resemble the syntypes, except in size.
Color. All the ethanol-preserved samples are gray.
Remarks. The morphology of all the additional S. caeruleum colonies collected from the Red Sea (Israel, Egypt, and Saudi Arabia) corresponds to the syntypes, but they may differ in size and in the density of the polyps emerging from the spreading membrane. All of the sequenced colonies (SMNHTAU_Co_ 34185, USNM 1201982, USNM 1201969, UF 9544 and UF 14223) were assigned to MOTU21 (McFadden et al. 2019). Based on the current findings, it is suggested that this species is the only representative of the genus present in the Red Sea.
Living features. The live colonies feature a membrane-like morphology with expanded polyps, whose color presents a bluish or light greyish-white tinge (Figs. 3B–C).
Distribution. Red Sea.