Pandanipora fragilis-a new deep-water cyclostome bryozoan from the subequatorial Mid-Atlantic Ridge, Atlantic Ocean, and a review of Pandanipora worldwide Author Grischenko, Andrei V. Department of Invertebrate Zoology and Aquatic Ecology, Biological Faculty, Perm State National Research University, Bukirev Street 15, GSP, Perm 614990, Russia & A. V. Zhirmunsky National Scientific Center of Marine Biology, Far East Branch, Russian Academy of Sciences, Palchevskogo Street 17, Vladivostok 690041, Russia Author Gordon, Dennis P. National Institute of Water & Atmospheric Research, Private Bag 19401 Kilbirnie, Wellington, New Zealand. Author Melnik, Viacheslav P. 0000-0002-0064-5162 Joint Stock Company Yuzhmorgeologiya, Federal Agency for State Property Management, Krymskaya Street 20, Gelendzhik, 353461, Russia. melnikvf @ rusgeology. ru; https: // orcid. org / 0000 - 0002 - 0064 - 5162 melnikvf@rusgeology.ru text Zootaxa 2020 2020-12-17 4895 4 594 600 journal article 9225 10.11646/zootaxa.4895.4.9 62735361-4a5a-4203-9251-be83966d5902 1175-5326 4358970 9558C85C-C5BF-4CA5-8D69-95B3CC2EA720 Pandanipora fragilis n. sp. ( Fig. 1 ) Diagnosis. Colony uniserial, linear, supported above substratum by straight, filiform, prop-like extensions, one per zooid. Branching of uniserial stem apparently regular along whole colony length. Autozooids tubular, thin-walled, with elongate proximal component forming part of continuous uniserial stem of colony, and distal peristomial tubes forming sharp angle with frontal wall of next zooid. Zooidal budding via development of partition from floor of parent zooid in its distal quarter to third, with proximal portion of daughter zooids not overlapping, and preceding and subsequent zooid not appressed along their proximal segments. Pseudopores exceptionally rare, slit-like, sparse on prop-like supports. Gonozooid, ancestrula and early astogeny unknown. Material examined. Holotype : ZIRAS 1 /50732, one colony fragment fractured into two smaller fragments, Polar Marine Geosurvey Expedition Сollection, cruise 41 of R . V . Professor Logachev , Stn 41L71, 17 January 2020, Mid-Atlantic Ridge , Atlantic Ocean , 13.22162° N , 44.75950° W , depth 3453 m , box-corer, collector A.M. Makoviz. Etymology. Latin, fragilis , fragile, alluding to the very delicate structure of the colony fragment. FIGURE 1. Pandanipora fragilis n. sp. Holotype, ZIRAS 1/50732. A. Light photomicrograph of colony fragment. B, D, E, H. General views of the first (B, E) and second (D, H) colony fragments, showing successively arranged zooids with no overlap. C. Lateral view of a tubular peristome. F. Single elongate prop from its inception in the zooid basal wall to the point of breakage. G. Enlargement of a prop, showing the slit-like pseudopores and axially embedded crystallites. I. Zooids at the point of colony bifurcation. J. Growing edge of the colony, showing the initial step of differentiation of a daughter zooid (lower) from the floor of the parent zooid (upper). K. Same, enlargement. L. Colony area at the point of bifurcation and new zooid differentiation. M. External zooidal wall, with pseudopores lacking. N. Floor of an autozooid, showing the communication pores between zooids. O. Oblique view of a peristomial aperture, showing the imbricated, foliated fabric of wedge-shaped crystallites. P. Enlargement of L, showing the different crystallite structures on the external and internal zooidal surfaces. Q. Enlargement of an external zooidal wall, showing the crystallites. R. Enlargement of the internal wall of a peristome, with an imbricated, foliated fabric of wedge-shaped crystallites having irregular margins. Scale bars: A, H, I, 250 μm; B, D, E, 500 μm; C, K, M, N, O, 50 μm; F, J, L, 100 μm; G, P, 25 μm; Q, 15 μm; R, 10 μm. Description. Colony fragment ( Fig. 1A ) comprising five zooids arranged in uniserial, branching chain, elevated above substratum by very thin, filiform, elongate, straight prop-like supports, one per zooid; body cavity of zooid continuous with that of prop. Zooidal chain more or less parallel to substratum, meandering in vertical profile. Branching of uniserial stem apparently consistent along entire length, with newly budded zooids diverging laterally at angles of c . 20–70° relative to parent zooids. Autozooids ( Fig. 1A, B, D, E, H, I ) tubular, thin-walled, vitreous, semitransparent, straight or, more often, concave and weakly undulating along their length; comprising proximal and distal components. Proximal component forming part of continuous uniserial stem of colony; distal component comprising slightly elevated peristome. Frontal peristomial surface remaining straight or just gently curving obliquely frontalwards from axial frontal surface; distal peristomial surface forming sharp angle of c . 50–75° with frontal wall of next zooid. Autozooidal wall gymnocystal (exterior-walled), with weak transverse striae or wrinkles ( Fig. 1H, I ), these are more visible in zooidal peristomes ( Fig. 1C ); at higher magnification, exterior surface constructed of wall-parallel needle-like crystallites ( Fig. 1P, Q ). Exceptionally rare tiny slit-like pseudopores ( Fig. 1G ) occurring sparsely on prop-like supports, but lacking on surface of zooidal walls ( Fig. 1L, M ). Peristomial opening circular or, more often, irregularly oval in outline, very thin-walled ( Fig. 1C, O ), gradually becoming thicker through accretion of additional layers of crystallites ( Fig. 1J, K ). Internal surface of peristome lined by distally imbricated foliated fabric of wedge-shaped crystallites ( Fig. 1R ). Zooidal axial and peristomial lengths varying little. Budding of daughter zooids achieved by development of partition from floor of parent zooid in its distal quarter to third ( Fig. 1A, B, D, E, H ) that slopes obliquely frontalwards or laterally under gently elevating peristomial portion, with completed parent zooid not overlapping proximal portion of daughter zooids; preceding and subsequent zooid thus not appressed along their proximal segments. Prop-like supports elevating colony above substratum, showing identical structure. One prop originating per autozooid in proximalmost area, near point where internal partitioning of daughter zooid takes place ( Fig. 1A, D, E, H ). Prop diameter varying little along entire length. Autozooids intercommunicating via series of circular communicative pores in floor of parent zooid ( Fig. 1N ). Gonozooid, ancestrula and early astogeny not seen. Measurements (mm). Colony fragment length 3.26, width 2.21, height 1.77. ZL, 1.291 –1.403 (1.337 ± 0.046) ( n = 4). PeL, 0.441 –0.494 (0.466 ± 0.025) ( n = 3). PeD, 0.124 –0.129 (0.126 ± 0.002) ( n = 3). ApL, 0.117 –0.125 (0.121 ± 0.004) ( n = 3). ApW, 0.102 –0.111 (0.107 ± 0.004) ( n = 3). PrL, 0.867 –1.822 (1.272 ± 0.403) ( n = 4). PrD, 0.035 –0.041 (0.038 ± 0.003) ( n = 4). Remarks. In possessing a linear, uniserial colony with elongate zooids having tubular peristomes and supported above the substratum by prop-like extensions, the new species clearly conforms to the characters of the monotypic genus Pandanipora . In general appearance, the type species ( P . helix ) and P . fragilis n. sp. have much in common. Notwithstanding their overall similarity, the two species differ in the following characters: 1) branching of the uniserial stem is uncommon and only occasionally seen near the colony origin in P . helix , but branching seems to be regular along whole colony length in P . fragilis n. sp. ; 2) zooids are closely appressed along proximal segments in P . helix , whereas zooids do not overlap, and newly budded zooids diverge from parental zooids in the distal quarter to third of the cystid in P . fragilis n. sp. ; 3) mean zooid length is considerably smaller in P . fragilis n. sp. than in P . helix (1.337 vs 1.628 –2.261 mm , respectively); 4) props are greatly variable in size and form in P . helix , but uniformly straight and filiform in P . fragilis n. sp. ; 5) prop mean diameter is much smaller in P . fragilis n. sp. than in P . helix (0.038 vs 0.082 –0.145 mm , respectively); 6) pseudopores in the zooidal wall of P . helix are mostly circular and widely distributed, whereas pseudopores are slit-like and occur only rarely in P . fragilis n. sp. , restricted to the props; 7) wedge-shaped crystallites on the internal surface of developing zooids of P . helix have straight margins, whereas corresponding crystallites in P . fragilis n. sp. have irregular, ragged margins.