Atlantisina atlantis, Berning & Harmelin & Bader & Cibio, 2017

Berning, Björn, Harmelin, Jean-Georges & Bader, Beate, 2017, New Cheilostomata (Bryozoa) from NE Atlantic seamounts, islands, and the continental slope: evidence for deep-sea endemism, European Journal of Taxonomy 347, pp. 1-51 : 8-10

Atlantisina atlantis gen. et sp. nov.

urn:lsid:zoobank.org:act:D2DA5614-66E4-4014-8FB5-7D931A22B5F2

Figs 1 C–D, 2A–F, Table 2

Diagnosis

Frontal shield translucent, surface densely covered by large, flattened, irregularly polygonal nodules; lateral walls well-developed, septular pores large, round to transversely oval. Orifice margin with six oral spines; condyles short and blunt, no suboral mucro. Ovicell hyperstomial, ooecium globular, a little longer than wide; ectooecium relatively narrow, covering (less than) the lower half of ooecium; exposed endooecium relatively large and hemispherical, surface topography irregular, with no distinct pattern. Ancestrula with a pyriform opesia and nine mural spines.

Etymology

Named after its type locality, Atlantis Smt; used as a noun in apposition.

Material examined

Holotype

ATLANTIS SMT: a large ovicellate colony marked “H”, together with three smaller colonies of A. atlantis gen. et sp. nov. and a young colony of Bathycyclopora suroiti gen. et sp. nov. (see below), on stylasterid skeleton, Stn 8 (MNHN-IB- 2014-45).

Paratypes

ATLANTIS SMT: 1 colony on biogenic substrate, Stn 4 (MNHN-IB- 2014-46); 3 colonies on a piece of stylasterid skeleton, Stn 7 (MNHN-IB- 2014-47); 2 colonies on a piece of stylasterid skeleton, Stn 7 (MNHN-IB- 2014-48); 1 coated colony on coral skeleton, Stn 8 (MNHN-IB- 2014-49); 3 colonies on rock, Stn 7 ( OLL 2016/122); 1 colony on coral, Stn 7 ( OLL 2016/123); 2 colonies on coral, Stn 7 ( OLL 2016/124).

Other material examined

ATLANTIS SMT: 3 colonies on coral skeleton, Stn 3 (unregistered MNHN material); 4 colonies on coral skeleton, Stn 4 (unregistered MNHN material); ca 33 colonies on coral and stylasterid skeletons, Stn 7 (unregistered MNHN material); 4 colonies on coral skeletons, Stn 8 (unregistered MNHN material); 6 colonies on coral, 1 on bivalve shell, Stn 7 ( OLL 2016/125); 3 colonies on coral skeleton, Stn 7 ( OLL 2016/126); 3 colonies on coral skeleton, Stn 7 ( OLL 2016/127); 1 colony on coral skeleton, Stn 7 ( OLL 2016/128); 8 colonies on stylasterid skeleton, Stn 7 ( OLL 2016/129).

Description

Colony encrusting, unilaminar, forming small irregular patches or biserial to triserial branching ribbons ( Fig. 2A ). Zooecium outline oval distally, triangular proximally, wedged in between proximal zooecia ( Fig. 2B ). Frontal shield matted vitreous, convex, densely covered by relatively large, evenly-spaced, irregularly polygonal and flattened nodules ( Fig. 2 C–F), imperforate except for five or six minute marginal pores, invisible in frontal view or in older zooecia; lateral walls well developed, septular pores in gymnocystal lateral walls large and surrounded by a distinct cryptocystal area, lateral ones usually transversely oval in outline, distal pore suborbicular, very slightly raised relative to lateral ones.

Orifice oval with a fairly straight and narrow proximal margin, slightly longer than wide, broadest in distal third, proximal third delimited by a pair of short and thick, blunt condyles oriented proximomedially; distolateral orifice margins with six short and closely-spaced spines arranged in two groups of three with a distinct distal gap, spine bases thick ( Fig. 2C ).

Ovicell hyperstomial, ooecium barely touching frontal shield of distal zooid or raised well above substratum when formed at colony margin, globular, with a short tubular proximal peristome wedged in between distalmost pair of spines and terminating at distal orifice margin, in general very little longer than wide; ectooecium smooth, encompassing lower half of ooecium; endooecium accordingly wellexposed, hemispherical, surface structure irregular, with an indistinct reticulate or nodular pattern; ooecial aperture taller than wide, acleithral ( Figs 1C , 2B, D ).

Ancestrula tatiform, almost oval in outline (ca 300 µm long, 190 µm wide), widest in proximal third, gymnocyst narrow and steeply sloping all around zooid except for proximal part, in which it is slightly better developed and more gently sloping, cryptocyst extremely reduced and only present at proximolateral margin, opesia extensive (ca 220 µm long, 150 µm wide), pyriform, distinctly constricted in distal third, surrounded by nine spines arranged in four closely positioned distal spines and five more widely spaced proximal ones; a single first-generation autozooid budded distally or distolaterally ( Fig. 2 E–F).

Remarks

Atlantisina atlantis gen. et sp. nov. occurs on the central NE Atlantic seamount complex together with A. meteor gen. et sp. nov. (see below), and both are also morphologically similar. The latter differs from the former in having eight instead of six oral spines, and in that the endooecial surface is more markedly nodular and similar to the zooecial frontal shield. In contrast, the endooecium in A. atlantis gen. et sp. nov. is less conspicuously and variably structured (faint ridges or nodules), and often even lacking any apparent structure (e.g., Fig. 1C ), being reminiscent of the early ontogenetic patterning of the frontal shield before the flattened nodules are formed. In some cases, however, a vague pattern of honeycomb depressions is visible, which is similar to the endooecial structure of several species found on or near the continental shelf (see below).

Another species with similar autozooids is Atlantisina inarmata gen. et sp. nov. from the Canary Islands (see below), which differs only in having slightly larger zooids and in that its skeleton is porcelain white, whereas it is translucent in A. atlantis gen. et sp. nov. A further important difference is found in the surface structure of the endooecium, which is densely and deeply pitted in A. inarmata gen. et sp. nov. The ooecium is also larger, and particularly wider, than in A. atlantis gen. et sp. nov.

Ecology

The sampled colonies of Atlantisina atlantis gen. et sp. nov. predominantly encrust coral skeletons, forming small patches or exploiting the surface via bi- or triserial ribbons. They have been found at depths between 275 and 460 m.

Distribution

The species is apparently endemic to Atlantis Smt in the central North Atlantic.

Figures

Fig. 1. Morphological characteristics of Atlantisina gen. nov. A. The kenozooidal ooecium of Atlantisina lionensis gen. et sp. nov. in lateral view (paratype MNHN-IB-2014-67), showing the broad band of ectooecium and the centrally exposed endooecium; note that the suboral crest is formed by smooth gymnocyst whereas the remaining frontal shield is cryptocystidean. B. Distal view of an autozooid of Atlantisina meteor gen. et sp. nov. showing two distolateral communication pores and the slightly raised central pore from which the ooecium is budded (paratype MNHN-IB-2014-50); note the broad band of cryptocyst bounding the septular pores, and that the remaining parts of the distolateral vertical walls and orifice are entirely gymnocystal. C. Oral region of an ovicellate zooid of Atlantisina atlantis gen. et sp. nov. (paratype MNHN-IB-2014-49), showing the contact between the cryptocystidean frontal shield and the gymnocystal distal part of the zooecium; note that the frontal shield is superpositioned on the condyles (white arrow) and meets the distolateral vertical walls in a sinusoidal suture (black arrow). D. Initial stages of zooid formation with the lateral walls being partly broken, showing the large basal pore chambers in Atlantisina atlantis gen. et sp. nov. (paratype OLL 2016/123). E. Slightly oblique view of the ancestrula of Atlantisina tricornis gen. et sp. nov. (paratype MNHN-IB-2014-64); note the simple tatiform morphology, the absence of a cryptocyst, and the slightly restricted oral region (top). Scale bars: A–B, D = 100 µm; C, E = 50 µm.

Fig. 2. Atlantisina atlantis gen. et sp. nov., Atlantis Smt. A. Overview of colony growing on a stylasterid skeleton; note the biserial-branching growth (paratype MNHN-IB-2014-47). B. Several autozooids and ovicellate zooids (paratype MNHN-IB-2014-49). C. Close-up of orifice and the base of a severed ovicell protruding from the distal communication pore (paratype MNHN-IB-2014-49). D. Ooecium (OLL 2016/127). E. Periancestrular region (paratype OLL 2016/123). F. Ancestrula and first-generation autozooid (paratype OLL 2016/123). Scale bars: A = 1 mm; B = 500 µm; C–D = 50 µm; E = 300 µm; F = 100 µm.