Exechonella nikitai, 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 : 52-54

Exechonella nikitai n. sp.

( Fig. 21 , Table 20)

Material examined. Five colonies on one piece of dead coral— Holotype: DPUV 2012-0007-0001. Indian Ocean , Maldive Islands, North Male Atoll, Kuda Haa, 04° 20' 914'' N, 073° 40' 778'' E, depth 8–35 m, 16 January 2008 . Paratypes: DPUV 2012-0007-0002 , DPUV 2012-0007-0003. Indian Ocean , Maldive Islands, North Male Atoll, Kuda Haa, 04° 20' 914'' N, 073° 40' 778'' E, depth 8–35 m, 16 January 2008 . IPUW 7017, IPUW 7018, Indian Ocean , Maldive Islands, North Male Atoll, Kuda Haa, 04° 20' 914'' N, 073° 40' 778'' E, depth 8–35 m, 16 January 2008 . Paratypes: DPUV 2012-0007-0004, on coral rubble. Indian Ocean, Maldive Islands, North Male Atoll , Vabbinfaru Island , depth 10 m, 3 August 2009, DPUV 2012-0007-0005 , on coral rubble. Indian Ocean , Maldive Islands, North Male Atoll, Vabbinfaru Island , House Reef , depth 5–19 m, 12–13 January 2008 . Additional material examined: DPUV 2012-0007-0006 , DPUV 2012-0007-0007, DPUV 2012-0007-0008, on coral rubble (mounted on SEM stubs and coated with gold). Indian Ocean, Maldive Islands, North Male Atoll, Vabbinfaru Island, House Reef , depth 5–19 m, 12–13 January 2008 . IPUW 7019, Indian Ocean, Maldive Islands, North Male Atoll, Angsana Ihuru Island, House Reef , depth 8 m, one colony, 28 July 2009 . DPUV collection, three non-numbered fragments (one on coral), mounted on SEM stubs and coated with gold.

Etymology. Named after the author’s son Nikita Ostrovskiy who collected this species.

Description. Colony encrusting, unilaminar, multiserial, sometimes producing uniserial offshoots. Autozooids convex, oval, separated by deep grooves. Primary orifice oval, wider than long, with smooth proximal shelf (a distalmost part of the zooidal frontal shield proximally surrounded by a wall of the peristome). Anter (distal half or more of primary orifice) is underlaid by an inner lamina, which ends form thick and rounded condyles directed downwards. Peristome tubular, with pustulose surface and flared rim visible in non-damaged zooids. In zooids of one colony the proximal edge of peristome had a wide U-shaped sinus. Frontal wall smooth, gently pustulose with 9–16 widely scattered foramina. Each foramen is a short tube with a rounded opening, and with its base often surrounded by a low ring-like elevation. Marginal pores small and rounded, observed around all zooidal periphery. Vertical zooidal walls narrow, represented by multiporous mural septula with communication pores arranged in one row. Avicularia unknown. Kenozooids are recognizable by a 5–12 small pores with centrally perforated cuticular plate. Ancestrula autozooidal, smaller than succeeding autozooids.

Remarks. Exechonella nikitai n. sp. is characterized by its tubular peristome, primary orifice oval with smooth proximal shelf and thick and rounded condyles directed downwards, frontal wall with scattered foramina as a short tube with a rounded opening, and also uniserial offshoots/branches (seen in some colonies).

Exechonella nikitai n. sp. is reminiscent to E. albilitus Tilbrook, 2006 ( Solomon Islands) and E. elegantissima n. sp. (Red Sea). The comparison between these three species shows the following differences: E. albilitus has 20– 30 prominent conical foramina with rounded opening (34 µm in diameter in average), whereas there are 9–18 small and short, conical or tube-like foramina with rounded or slit-like openings (18 µm) in E. elegantissima n. sp., and 9–16 tube-like foramina with rounded opening (40 µm) and often with a ring-like elevation around its base in E. nikitai n. sp., sometimes also seen in E. elegantissima n. sp. The former species also has the largest zooidal size. In one colony of E. nikitai n. sp. zooids had peristomes with a sinus similar to that in E. elegantissima n. sp., but it was much wider in the former species.

Maldive Islands, Indian Ocean Tilbrook (2006, p. 115) mentioned that a specimen from the Maldives (kept at the Natural History Museum, London) “appears to be” E. albilitus , and its further comparison with other species having ‘elevated’ frontal foramina is required to make a more precise conclusion.

Distribution. E. nikitai n. sp is only known from Maldive Islands (North Male Atoll, Vabbinfaru Island, Angsana Ihuru Island and Kuda Haa), Indian Ocean.

Figures

FIGURE 21. Exechonella nikitai n. sp. Indian Ocean, Maldive Islands (A ‒ C, E, G, H: paratype DPUV 2012 - 0007 - 0006; D: paratype DPUV 2012 - 0007 - 0007; F: DPUV 2012 - 0007 - 0008). A, B, general colony view from above (in B peristomes have a sinus). C, D, lateral view of colony showing shape of peristomes and multiporous mural septulum. Kenozooids shown by arrows (in C). E, lateral view of autozooid showing shape of foramina, peristome, marginal pores and multiporous mural septulum. Kenozooid shown by arrow. F, close-up of autozooids (view from above). G, ancestrula (to the right) and two distal zooids. H, details of primary orifice and peristome. Condyle shown by arrow. Scale bars: A, B, D = 1 mm; C, E ‒ H = 100 µm.