Discantenna metallica, 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 : 21-25

Discantenna metallica n. sp.

( Figs 2I , 10–12 )

Material examined. Holotype: ZIRAS 1/50675, colony detached from nodule, YMG R.V. Yuzhmorgeologiya cruise YMG4–06, Stn 67, 8 August 2006, 13.18842° N, 134.51227° W, 4820 m. Paratype 1: ZIRAS 2/50676, colony detached from nodule, YMG R.V. Gelendzhik cruise GLD4–11, Stn 224, 2 May 2012, 12.55585° N, 133.08295° W, 4778 m. Paratype 2: ZIRAS 3/50702, colony detached from nodule, YMG R.V. Yuzhmorgeologiya cruise YMG18–01, Stn 37, 29 August 2003, 13.85300° N, 129.08458° W, 4715 m. Additional material: YMG4–06, Stns 69, 82; GLD4–08, Stn 151; GLD4–11, Stns 207, 225; YMG4–14, Stns 358, 362. Total specimens examined 11.

Etymology. Latin, metallica , pertaining to a mineral, alluding to the substratum.

Description. Colony erect, white, stalked, from narrow encrusting base ( Fig. 11K ). Initially uniserial, becoming biserial, distal end of base developing erect column that expands into shallow circular or irregular discoidal structure, up to 3.45 mm diameter, in which zooids are centripetally arranged; colony height up to 4.94 mm.

Apical disk bereniciform ( Fig. 10A, B ); up to 52 zooidal peristomes, angled obliquely outwards from depressed center of disk; peripheral common bud thin, with narrow marginal lamina pierced by pseudopores and having skeletal microstructure of distally imbricated foliated crystallites. Calcified terminal diaphragms ( Figs 10F , 11A, G, M ) common in older, proximal zooids; diaphragms made up of fused sectors of needle-like crystallites ( Fig. 11F ); 2–5 tiny pseudopores apparent.

Only two gonozooids seen, each produced at edge of small capitulum of unattached stem ( Fig. 11A ). Stem with ~10 short peristomes of varied length, ~6 of them with apertures occluded by diaphragms. Capitulum with irregular profile in apical view owing to many peristomes broken at base; made up of four ‘sectors’, each comprising fused parts of adjacent peristomes, one of which bears gonozooid. Gonozooid broader than long ( Fig. 11C–E ), with broadly W-shaped margin on capitulum side ( Fig. 11B ) or this not evident ( Fig. 11C ); moderately inflated frontally either side of shortly projecting ooeciostome ( Fig. 11C, I ) with near-circular ooeciopore with thin slightly irregular rim ( Fig. 11D, E, H, I ). Gonozooid wall with greater pseudopore density.

Ancestrula suberect, protoecium inclined at 50–60° angle to substratum ( Fig. 12A, C, D, E, H ). Protoecium may be shortly flared at base ( Fig. 12H ), continuous with peristome, surface with needle-like crystallites and sparse pseudopores. Abfrontal sides of ancestrular zooid, 3–4 daughter zooids and base of colony of erect fascicle of zooids supported by basal layer and skirt of kenozooids and extrazooidal calcification ( Fig. 12B, F ); base of skirt with irregular margin depending on substratum; exterior surface marked by vertical striae and ridges ( Fig. 12H ), and moderately sparse but evenly distributed pseudopores.

Daughter zooid distal to ancestrula initiating biseriality by budding two additional zooids, their respective peristomes directed to left and right ( Fig. 12E, F, H ), after which 5–11 additional peristomes may be produced around base of what will become erect stem of capitulum ( Fig. 12I –L ), which shows chambers of seven (some as small proximal ends) in cross section in one example ( Fig. 12J ). Non-functioning older zooids with closure plates, near or below peristomial rim ( Figs 11 , 12A, K ).

Measurements (mm). Holotype, ZIRAS 1/50675 ( Fig. 10A–D ): Colony height 2.95; capitulum length 4.15, width 3.45; stalk cross-section at point of breakage 0.35 × 0.40; stalk cross-section at junction with disk 0.71 × 0.53; stalk height (from point of breakage to disk) 1.53. Disk zooids: ZL 0.772–1.295 (0.979 ± 0.166); PeL 0.221–0.713 (0.414 ± 0.179); PeD 0.123–0.140 (0.131 ± 0.005); ApL 0.132–0.171 (0.151 ± 0.013); ApW 0.098–0.132 (0.115 ± 0.012). Stalk zooids (n = 4): ZL 0.543–0.628 (0.583 ± 0.035); PeL 0.142–0.211 (0.172 ± 0.029); PeD 0.135–0.148 (0.141 ± 0.006); ApL 0.113–0.128 (0.122 ± 0.006); ApW 0.103–0.123 (0.112 ± 0.009).

Paratype 1, ZIRAS 2/50676 ( Figs 10E–I , 11C, E, H, I ): Colony height 4.94. Stalk: height (substrate to disk) 3.57, cross-section (narrowest, near ancestrula) 0.45 × 0.33, cross-section at junction with disk 0.58 × 0.38. Disk zooids (n = 5): ZL 0.995–1.731 (1.342 ± 0.261); PeL 0.358–0.818 (0.456 ± 0.202); PeD 0.133–0.152 (0.143 ± 0.007); ApL 0.151–0.178 (0.164 ± 0.012); ApW 0.118–0.136 (0.130 ± 0.006). Stalk zooids (n = 4): ZL 0.698–0.953 (0.834 ± 0.126); PeL 0.078–0.103 (0.092 ± 0.010); PeD 0.138–0.161 (0.150 ± 0.011); ApL 0.128–0.147 (0.136 ± 0.008); ApW 0.122–0.130 (0.126 ± 0.003). Gonozooid (n = 1): GZL 0.406; GZW 0.483; GZH 0.352; OsL 0.114; OsD 0.117–0.077; OpD 0.067.

Paratype 2, ZIRAS 3/50702 ( Fig. 11A, B, D ): Gonozooid (n = 1): GZL 0.337; GZW 0.561; GZH 0.294; OpL 0.072; OpD 0.078.

Non-type specimen YMG4–14, Stn 358 ( Fig. 12A–D ): AnPeD 0.115 (n = 1).

Remarks. Discantenna metallica n. sp. is only the second known species. The type species, D. tumba , was described from 943–1097 m depth on the Chatham Rise, New Zealand. Inter alia, D. metallica differs from it by achieving a larger colony size (> 4 mm high and wide, cf. <2.6 mm high and wide in D. tumba ) with many more peristomes in the elevated disk (~52, cf. ~24) having a diameter up to 0.17 mm (cf. 0.08 mm). Whereas tubular peristomes are arranged along only the frontal side of the stem in D. tumba (with the abfrontal side pseudoporous), such peristomes alternate around the stem in a spiral pattern in D. metallica . Stem peristomes are short in D. tumba , but can be quite elongate in D. metallica , some exceeding the radius of the disk. Interestingly, even though disk size is bigger in D. metallica , the only specimens with a gonozooid had incompletely developed capitula. Whereas the incubation chamber in D. tumba is set back from the edge of the capitulum, that in D. metallica projects a little from the margin, with the ooeciostome outermost. The gonozooid in D. metallica n. sp. resembles that in the following new genus and species, which we attribute to the Oncousoeciidae .

Distribution. Recorded from 10 stations within coordinates 12.55585– 14.37702° N, 129.08458– 134.51227° W, at depth range 4715–5238 m.

Figures

FIGURE 2. Colonies of some cyclostome bryozoans, in vivo, attached to polymetallic nodules. A–E, Pandanipora helix n. gen., n. sp.: A, specimen GLD4–09, Stn 190; B, specimen GLD4–12, Stn 262; C, specimen YMG4–07, Stn 143; D, specimen YMG4–13, Stn 295; E, specimen GLD 4–11, Stn 212. F, Tubuliporina sp. indet., specimen YMG18–01, Stn 7. G, H, Abyssoecia elevata n. gen., n. sp.: G, specimen GLD4–09, Stn 196; H, specimen GLD4–09, Stn 191. I, Discantenna metallica n. sp.: specimen GLD4–11, Stn 224. J, K, Frontohornera frontalis n. gen., n. sp.: J, specimen YMG4–07, Stn 124; K, specimen GLD4–11, Stn 210. L, Alyonushka hystricosa n. gen., n. sp.: specimen GLD4–09, Stn 199. M, Calyssopora volcano n. gen., n. sp.: specimen YMG18–01, Stn 33. N, O, Anyuta anastema n. gen., n. sp.: N, specimen GLD4–09, Stn 180; O, specimen YMG4–06, Stn 71. Scale bars: 1 mm.

FIGURE 10. Discantenna metallica n. sp. Holotype and paratype colonies. A–D, holotype, ZIRAS 1/50675; E–I, paratype 1, ZIRAS 2/50676. A, apical and B, lateral views of colony; C, D, same, edge of disk, respectively showing peristomes and differentiating zooids; E, lateral view of colony showing numerous stalk zooids; F, autozooidal peristome near top of stalk with calcified terminal diaphragm; G, underside of part of capitulum seen in E; H, part of stalk with short peristomes and terminal diaphragms; I, margin of capitulum seen in E. Scale bars: A–E, 500 µm; F, 150 µm; G–I, 250 µm.

FIGURE 11. Discantenna metallica n. sp. Paratype and other colonies. A, B, D, F, G, paratype 2, ZIRAS 3/50702; C, E, H, I, paratype 1, ZIRAS 2/50676; J, L, N, P, specimen YMG4–06, Stn 69; K, M, O, Q, specimen GLD4–08, Stn 151. A, fertile colony with broken base and small capitulum; B, D, same, showing gonozooid in frontal and apertural views; C, E, a second gonozooid with longer ooeciostome; F, G, high- and lower-magnification views of terminal diaphragm, showing skeletal microstructure; H, I, ooeciopores of gonozooid in C and E; J, N, lateral and apical views of colony with small lobate capitulum; K, O, lateral and apical views of another colony with a small capitulum that is more symmetrical; L, M, parts of stalks with short autozooidal peristomes and terminal diaphragms; P, Q, proximal parts of two colonies in post-ancestrular region. Scale bars: A, J, K, N, O, 250 µm; B–E, L, M, P, Q, 100 µm; F–I, 25 µm.

FIGURE 12. Discantenna metallica n. sp. Progressive stages of development of ancestrulate and young colonies. A–D, specimen YMG4–14, Stn 358; E–H, specimen GLD4–11, Stn 224; I–L, specimen GLD4–11, Stn 207. A–D, rotational views (respectively frontal, distolateral, lateral, proximal) of newly formed colony with ancestrular zooid and developing daughter peristome; note developing kenozooids in B; E–H, similar views of a slightly older colony with further kenozooidal development in F; I–L, apical and profile views of an older colony (ancestrular protoecium missing) with a definite stalk underway and peristomes opening all around it. Scale bars: A–H, J, 100 µm; I, K, L, 200 µm.