Orectopora flabellum, Grischenko & Gordon & Melnik, 2018

Grischenko, Andrei V., Gordon, Dennis P. & Melnik, Viacheslav P., 2018, Bryozoa (Cyclostomata and Ctenostomata) from polymetallic nodules in the Russian exploration area, Clarion - Clipperton Fracture Zone, eastern Pacific Ocean-taxon novelty and implications of mining, Zootaxa 4484 (1), pp. 1-91: 15-19

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Orectopora flabellum

n. sp.

Orectopora flabellum   n. sp.

( Figs 6–8 View FIGURE 6 View FIGURE 7 View FIGURE 8 , 51 View FIGURE 51 )

Material examined. Holotype: ZIRAS 1/50673, colony detached from nodule, YMG R.V. Yuzhmorgeologiya cruise YMG4–13, Stn 316, 3 August 2014, 13.09428° N, 132.37362° W, 4933 m. Paratype: NIWA 127723, colony detached from nodule, YMG R.V. Gelendzhik cruise GLD4–12, Stn 258, 10 April 2013, 12.90213° N, 132.87047° W, 4713 m. Additional material: YMG4–07, Stns 126, 136; GLD4–08, Stns 145, 151; GLD4–09, Stns 183, 198; GLD4–11, Stns 219, 230; YMG4–13, Stn 273; YMG4–14, Stns 332, 363, 365. Total specimens examined 14.

Etymology. Latin, flabellum   , a fan, used as a noun in apposition.

Description. Colony erect, flabellate, subplanar and narrowly compressed, attached by short stalk ( Fig. 6A, C View FIGURE 6 ), white. Initially with single spreading fan of zooids, more or less bilaterally symmetrical, or shortly branching as 2–3 flattened lobes, entire fan gently concave frontally, convex abfrontally ( Fig. 6B, D, E View FIGURE 6 ). At inception, first major lobe(s) comprising bilaterally compressed fascicle(s) of 10–12 autozooids, before subdivision into smaller lobes ( Fig. 8E –O View FIGURE 8 ). Colony and lobes essentially 1–2-layered, comprising, in transverse section, initially contiguous, but then laterally diverging, autozooidal tubes, backed by discontinuous series of smaller kenozooidal tubes ( Figs 6E View FIGURE 6 , 7A, C, F View FIGURE 7 , 51A, B, D, E View FIGURE 51 ). Surface of colony textured by series of thin sinuous growth lines ( Figs 6D View FIGURE 6 , 7B, E, H View FIGURE 7 ) and needle-like crystallites perpendicular to growth lines. Simple pseudopores opening externally, seemingly moderately sparse in SEM images, but more obvious and abundant in CT scans, more or less regularly distributed ( Figs 7B, E View FIGURE 7 , 51A –F View FIGURE 51 ).

Autozooidal tubes mostly very long, with several running length of colony; other tubes shorter, originating by lateral budding in plane of colony as fascicles broaden ( Fig. 51A, C View FIGURE 51 ). Earliest-established peristomes more evident on colony faces by bulging of their longitudinal tubes, secondarily budded autozooids not bulging or less obviously so ( Figs 6A, E View FIGURE 6 , 8L View FIGURE 8 ). Openings of primary and secondary autozooidal tubes at colony margin evidenced by their circular to subcircular rims, some separated sublaterally by shafts of slightly smaller diameter ( Fig. 7A, B, D, F View FIGURE 7 ), interpreted to be proximal parts of differentiating autozooids. Interior surface of zooidal tubes lined by distally imbricated foliated fabric of wedge-shaped crystallites ( Fig. 7D, G, J View FIGURE 7 ).

Kenozooids seen in transverse section at colony margin, 1–2 on abfrontal side of each autozooid ( Fig. 7A, C, F, I View FIGURE 7 ), with round to subtriangular rims. Interior surface ultrastructure as in autozooids. CT scans reveal kenozooids to be long, irregular structures descending behind or to the side of zooidal tubes ( Fig. 51B, D, E View FIGURE 51 ), occasionally communicating with neighbors via interzooidal pores, with more-numerous pseudopores to outer surface. Proximally, CT scans reveal kenozooidal chambers transition from elongate tubes to layers of squatter cushion- or amoeba-shapes ( Fig. 51A, B, F View FIGURE 51 ); each kenozooid communicating with neighbors above and below; those closer to outer surface with sparse pseudopores. Kenozooids also in axils between fascicle lobes.

Gonozooid not seen.

Ancestrula suberect, inclined at 45–55° angle to substratum ( Fig. 8B, N View FIGURE 8 ). Protoecium ( Fig. 8D View FIGURE 8 ) flared at base, with slightly smoother margin, continuous with peristome, surface with needle-like crystallites (interpreted as eroded planar-spherulitic fabric) and sparse pseudopores. Abfrontal sides of ancestrular zooid, one suberect zooid and base of erect fascicle of zooids supported by developing skirt of kenozooids and extrazooidal calcification ( Fig. 8B, E, N View FIGURE 8 ); skirt with scalloped margin depending on substratum ( Fig. 8P View FIGURE 8 ); exterior surface marked by vertical striae and ridges, and moderately sparse but evenly distributed pseudopores.

Measurements (mm). Holotype, ZIRAS 1/50673 ( Fig. 6 View FIGURE 6 ): Colony height c. 2.07 (proximal end of largest colony broken), width 3.02; three main lobes (fascicles) length 0.48–1.01, width 0.43–1.51, thickness 0.09–0.16; ‘stalk’ at point of breakage 0.33 × 0.17; ZL 1.308–1.853 (1.604 ± 0.198); PeL 0.043–0.163 (0.082 ± 0.035); PeD 0.123–0.154 (0.136 ± 0.009); ApL 0.094–0.105 (0.099 ± 0.003); ApW 0.086–0.098 (0.091 ± 0.004).

Non-type specimen GLD4–08, Stn 151 ( Fig. 8D View FIGURE 8 ): AnPeD 0.106 (n = 1).

Remarks. Orectopora flabellum   n. gen., n. sp. is represented in the Russian-sector collection by 14 specimens having varied size and maturity. The novel features of this taxon defy inclusion in a named family and have required some interpretation to describe and explain them, facilitated by light microscopy, with and without staining, plus SEM and micro-CT. The form of the ancestrular zooid is similar to that in Pandanipora   n. gen., and the initial colony form, comprising a short ascending series of zooids supporting an elevated structure, is reminiscent of that in Discantenna ( Gordon & Taylor, 2010)   .

Distribution. Recorded from 14 stations within coordinates 12.65038– 14.57215° N, 131.73948– 134.71841° W, at depth range 4713–5275 m.