Exechonella similis, 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 : 43-45

Exechonella similis n. sp.

( Fig. 17 , Table 16)

Exechonella brasiliensis: Tilbrook et al. 2001 , p. 65, fig. 8g.

? Exechonella brasiliensis: Winston & Heimberg 1986 , p. 15, figs 26–27.

Material examined. Holotype: MTQ G 100216, on coral rubble (mounted on SEM stub and coated with gold). Coral Sea , Great Barrier Reef , Lizard Island, Cobey Hole, depth 16 m, 8 October 2012 . Paratypes: DPUV 2016- 0001-0002 , DPUV 2016-0001-0003 (on bivalve shells, non-cleaned, mounted on SEM-stubs, uncoated). Coral Sea , Great Barrier Reef , Lizard Island, Watson Bay, depth 6.5 m, 4 October 2012 .

Etymology. The name given because of very close similarity of this species to E. azeezii n. sp. Derived from the Latin word “ similis ” (similar).

Description. Colonies encrusting, unilaminar, multiserial. Zooids pentagonal or hexagonal separated by a narrow deep groove. Primary orifice almost subcircular, wider than long, poster as wide as the anter but slightly smaller in size, both predominantly of rounded outline. Anter wall underlain by an inner lamina that ends in the mid-lateral side, to form triangular or oval elongate condyles, with pointed or rounded tips extending medially and beyond the edge of the step-like curve below. Peristome is low, collar-like, slightly flared, with a pustulose external surface. The proximal edge of the peristome normally with a prominent or soft central fold-like projection. In the ancestrular area peristome could have up to four such projections, distal, proximal and two lateral. Frontal shield convex, pustulose, evenly covered with 21–36 circular or oval, well-separated foramina, with a relatively narrow raised rim with a peripheral inner wall surface and smooth or slightly wrinkled gymnocystal sloping walls, surrounding a central lumen. Fusions between foraminal rims are not common in most zooids. Small round or oval marginal pores are obvious. Vertical zooidal walls with multiporous mural septula with one row of communication pores. Lateral avicularia are frequent, developing in either or both lateralmost foramina, which are larger than of the other foramina; each avicularium is situated on the outer (often raised) edge of a foramen obvious as a shallower or deeper depression (sometimes surrounded by a low rim) with a central button-like elevation with thick walls (sometimes cylindrical with thin walls) and a central pore. Oval or triangular kenozooids are frequent, often associated with avicularia, with a frontal surface having 4–7 small pores each with centrally perforated cuticular plate. Ancestrula autozooid-like, smaller or the same size.

Remarks. Exechonella similis n. sp. is reminiscent of E. azeezi n. sp. in most characters. The main difference between these two species is the shape of the primary orifice typically subcircular with the anter and poster having the same width in the former species, and the poster typically more angular and narrow in the latter species. Both E. similis n. sp and E. azeezi n. sp. differ from E. brasiliensis by the primary orifice that is wider than long, pustulose surface of the peristome and the smaller foramina, button-like shape of the central element of avicularium, and the larger size of the lateralmost foramina (with avicularium) in comparison with the rest of the frontal foramina. The specimen from Komodo described by Winston and Heimberg (1986) should be additionally studied for comparative purposes.

Distribution. Exechonella similis n. sp. has a west Pacific distribution including the areas of Vanuatu and Lizard Island, Great Barrier Reef.

Lizard Island, Great Barrier Reef

Figures

FIGURE 17. Exechonella similis n. sp. Great Barrier Reef, Lizard Island (A: paratype DPUV 2016 - 0001 - 0002; F, G: paratype 2016 - 0001 - 0003; B ‒ E, H: holotype MTQ G 100216). A, general view of non-cleaned colony from above. Peripheral zooidal buds with membranous frontal wall are well seen. Peristomes with processes are seen in some zooids in the central colony part. B, E, F, close-up of autozooids. Some lateralmost foramina with avicularia shown by arrows in B. C, peripheral part of the colony, showing peristome shape and multiporous mural septula. D, close-up of autozooid showing details of primary orifice and peristome. G, non-cleaned lateralmost foramen with avicularium. Arrowhead shows an edge of mandible. H, close-up of lateralmost foramen with avicularium associated with kenozooid in cleaned colony. Pores of kenozooid have centrally perforated cuticular plates. Scale bars: A = 1 mm; B ‒ E = 100 µm; F = 500 µm; G = 50 µm; H = 10 µm.