Arturia sueziana (Klautau & Valentine, 2003)

Figures 4a–f

Clathrina canariensis var. compacta; Row 1909: 184 (not: Schuffner, 1877).

Clathrina sueziana Klautau & Valentine, 2003: 43, fig. 35.

Arthuria sueziana; Voigt et al. 2017: 15, figs 9a–h.

Material examined. RMNH Por. 9537, Saudi Arabia, Jeddah, near Thuwal, Al Bilut (Rose Reef), 22.309861°N 38.886472°E, depth 12 m, scuba, coll. N.J. de Voogd, field nr. THU03/JED022, 7 November 2014 ; RMNH Por. 10112, Maldives, Faafu Atoll, Free Climbing, 3.066583°N 72.923028°E, depth 15 m, scuba, coll. N.J. de Voogd, field nr. MAD06 /MAS067, 18 February 2015 .

Description. Relatively massive, rounded to conical cormi of tightly anastomosed tubuli, converging at the upper surface to a few wide, tapering oscular (water-collecting) tubes (Figs 4a–c). Overall size is up to 3 x 1.5 x 1.5 cm, tubuli diameters 0.2–0.5 mm, water-collecting tubes up to 8 mm in diameter. Color pale yellow or dirty white.

Aquiferous system. Asconoid.

Skeleton. (Figs 4d) The tubule wall has two or more layers of overlapping triactines and tetractines, the latter with the apical actines protruding in the tubar lumen. The ratio of triactines vs. tetractines was 7: 1 in RMNH 9537 and 7.5: 1 in RMNH 10112, a clear predominance of triactines.

Spicules. (Figs 4e–f) Triactines and tetractines; trichoxeas were observed in a very low frequency in all samples, invariably broken.

Triactines (Figs 4e) predominantly equiradiate and equiangular, but a few are sagittal with paired actines wingshaped. Actines conical, actine lengths in the various specimens:

RMNH Por. 9537: 96– 128.8 –146 x 8.5– 10.5 –14.5 µm (paired and unpaired actines of sagittal triactines of approximately same length).

RMNH Por. 10112: 48– 111 –153 x 6 – 11.8 –15 µm (ditto).

Tetractines (Fig. 4f) with basal triradiate system predominantly equiradiate, occasionally sagittal, with apical actines smooth, thinner, but up to the same length of the actines of the basal triradiate system. Basal actines conical, actine sizes in the various specimens:

RMNH Por. 9537: 36– 119.4 –147 x 4 – 10.7 –14 µm, apical actines 54– 104.4 –164 x 4 – 4.9 –7 µm.

RMNH Por. 10112: 64– 115 –156 x 6 – 10.2 –13 µm, apical actines 32– 84 –153 x 4 – 5.7 –8.5 µm.

Distribution and ecology. Red Sea (Suez; Thuwal Reefs, near Jeddah), Maldives, in reef localities under overhangs.

Remarks. This is the first time the species has been recorded from outside the Red Sea. The habitus and spicular characters of the Jeddah and Maldives specimens in our collection are so close that conspecificity seems obvious. There are some spicule size differences with the Suez holotype (tetractines are only up to 98 µm, apical actines of the tetractines are only up to 63 µm). In Voigt et al. ’s (2017) specimens there was a clear presence of trichoxeas (also mentioned in the holotype, quite rare in the present material). However, trichoxeas are notoriously variable in Clathrinidae, and the habitus and overall characters match with all three records.

We obtained a partial 28S rRNA sequence for the Maldives specimen (sequencing of our Red Sea specimen failed). The Maldives sequence ended up in the same clade together with three Red Sea sequences from Voigt et al. (2017) in a high bootstrap support (cf. Fig. 2C). Nevertheless, the identical Red Sea sequences together differed substantially from the Maldives sequence (in more than 10 sites), indicating a possible specific difference, which may become evident when more studies of Western Indian Ocean localities have been made.

Arturia darwinii (Haeckel, 1872) was reported from Zanzibar by Jenkin (1908) as Clathrina . It was described as bright lemon-yellow in color and the tri-and tetractines had basal actines 60–120 x 12–16 µm, with the apical actines of the tetractines having the same length but thinner (8 µm). These measurements overlap with the above given data on A. sueziana . The species is also reported from the Mozambique Channel by Barnes & Bell (2002), but no description was given. The type locality of A. darwinii is Java, Indonesia (cf. Van Soest & De Voogd 2015), but Haeckel also reported specimens from the Red Sea. The distinction between A. darwinii and A. sueziana remains to be further established.

All the above presented discrepancies with the holotype of A. sueziana support Klautau & Valentine’s (2003) statement that A. sueziana is a complex of species.