Exechonella claereboudti, Cáceres-Chamizo & Sanner & Tilbrook & Ostrovsky, 2017

Cáceres-Chamizo, Julia P., Sanner, Joann, Tilbrook, Kevin J. & Ostrovsky, Andrew N., 2017, Revision of the Recent species of Exechonella Canu & Bassler in Duvergier, 1924 and Actisecos Canu & Bassler, 1927 (Bryozoa, Cheilostomata): systematics, biogeography and evolutionary trends in skeletal morphology, Zootaxa 4305 (1), pp. 1-79 : 45-47

Exechonella claereboudti n. sp.

( Fig. 18 , Table 17)

Material examined. Holotype: DPUV 2012-0003-0001 , on bivalve shell (mounted on SEM stub and coated with gold). Indian Ocean , Oman, Salalah, near Mirbat, maximal depth 8.3 m, 18 January 2009 . Paratype: DPUV 2012- 0003-0002 , on bivalve shell (mounted on SEM stub, uncoated). Oman, Salalah , near Mirbat (right side of the “ Kelp Bay ”), maximal depth 9.4 m, 16 January 2009 .

Etymology. Named after the marine biologist Dr. Michel Claereboudt who organized and led the dive works in Oman during which this species was collected.

Description. Colonies encrusting, unilaminar, multiserial. Autozooids pentagonal, hexagonal or oval in shape, slightly convex, separated by narrow grooves. Orifice oval, wider than long. Larger anter rounded whereas smaller poster typically angular (quadrate-like with rounded 'corners') or shallow rounded in some zooids. Anter wall underlain by an inner lamina which ends form prominent triangular condyles, with pointed or, sometimes, rounded tip extending beyond the edge of the step-like curve below. Peristome low, collar-like, flared, with pustulose external surface. When seen from above it has oval outline, often wider proximally, and sometimes with parallel lateral sides. Peristome edge bears 3–5, long fold-like projections/spikes, 0–2 distal, two lateral and one proximal. Frontal shield smooth, evenly covered with 34–50 rounded and oval, closely spaced foramina bordered by a relatively wide raised rim with a peripheral inner wall surface and smooth or slightly wrinkled gymnocystal sloping walls, surrounding a central lumen. Fusions of foraminal rims are frequent, forming chains of 2–3 foramina. Marginal pores are easily observed all around zooidal periphery. Vertical zooidal walls wide, represented by multiporous mural septula with 1–3 rows of communication pores. Avicularia present in one or both larger lateralmost foramina of most zooids. They are represented by a depression surrounded by a low rim with a buttonlike central structure with a central pore. Kenozooids are frequent, associated with avicularia, having 6–11 pores with a centrally perforated cuticular plate. Ancestrula autozooidal, smaller than zooids of the first generation.

Oman, Indian Ocean Remarks. Exechonella claereboudti n. sp. is reminiscent both E. azeezi n. sp. and E. similis n. sp. differing from them by (1) peristome, normally wider proximally than distally when seen from above, with long spike-like projections (distal, lateral and proximal) on its rim, whereas in E. azeezi n. sp. and E. similis n. sp. the peristome is often narrower proximally, usually having only one proximal central projection; (2) orifice shape with typically quadrate (less often shallow rounded) poster as wide as anter (in E. claereboudti n. sp.), typically rounded poster as wide as anter (in E. similis n. sp.) and typically angular poster narrower than the anter (in E. azeezi n. sp.) (some variation between angular and rounded outline of the poster present in all species); (3) number of frontal foramina 30–50 in E. claereboudti n. sp. (even in a young colony studied, the first zooidal generation, including ancestrula, has over 40 foramina), compared with 18–31 of E. azeezi n. sp. (Red Sea) and 13–35 ( Maldives) and 21–36 in E. similis n. sp. The high number of the foramina also results in common fusion of their rims in the former species, but this was not common it two latter species.

Distribution. Exechonella claereboudti n. sp. was only found in the Indian Ocean, Oman, Salalah, near Mirbat.

Figures

FIGURE 18. Exechonella claereboudti n. sp. Indian Ocean, Oman (A ‒ H: holotype DPUV 2012 - 0003 - 0001). A, general view of holotype from above. B, peripheral part of holotype (frontal view): primary orifices have either quadrate or shallow rounded poster. C, lateral view of peripheral part of holotype showing shape of peristomes and multiporous mural septula. D, close-up of several peripheral autozooids. Some lateralmost foramina with avicularium shown by arrows. E, ancestrular zone of holotype with ancestrula in the centre. F, H, details of primary orifice with shallow rounded poster and peristome. G, close-up of lateralmost foramen with avicularium associated with kenozooid in cleaned colony. Pores of kenozooid have centrally perforated cuticular plates. Marginal pores are visible in this and neighbour zooids. Scale bars: A, B = 1 mm; C ‒ H = 100 µm.