Atlantisina, 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 : 5-8

Genus Atlantisina gen. nov.

urn:lsid:zoobank.org:act:B1994BA0-3091-4D78-A5C3-CE8BEE1A19D2

Type species

Atlantisina atlantis gen. et sp. nov.

Diagnosis

Colony encrusting, unilaminar, forming small patches or biserial to multiserial ribbons by intrazooidal budding. Frontal shield umbonuloid, imperforate except for very few minute marginal pores; gymnocystal lateral walls generally extensive, basal pore chambers present, communication via a single large exterior pore per neighbouring zooid that is bounded by a variably distinct cryptocystal rim, a single round and slightly raised septular pore present in the distal vertical wall. Orifice with condyles, proximal margin concave; oral spines present, paired, in two distolateral series with a distal gap. Ovicell hyperstomial, ooecium kenozooidal, budded from the maternal zooid through the distal septular pore; ectooecium partially calcified, proximally usually forming a short tubular apertural peristome wedged in between the distalmost pair of spines; calcified endooecium exposed in central area, surface variably structured, occasionally deeply pitted but imperforate; not closed by operculum (presumably acleithral). No avicularia. Ancestrula tatiform, gymnocyst fairly narrow all around, cryptocyst absent, opesia extensive, slightly constricted in distal (oral) part, surrounded by numerous mural spines; first generation autozooid single, budded distally or (disto)laterally.

Etymology

Named for the occurrence of the type species on Atlantis Smt. Gender feminine.

Remarks

The combined occurrence of the following features distinguishes Atlantisina gen. nov. from all romancheinid genera as well as from the other new genera presented here: (i) a partly calcified ectooecium, (ii) the exclusively kenozooidal origin of the ooecium that is produced from a distinct communication pore in the maternal zooid’s distal wall, (iii) the lack of avicularia, and (iv) the well-developed lateral walls, with a single large communication pore per neighbouring zooid.

The variably developed band of smooth ectooecium around the basal and proximal part of the ooecium is a distinctive character of Atlantisina gen. nov. species ( Fig. 1A ). Moreover, in the Romancheinidae and most of the remaining atlantisinids the ooecium is either produced by the zooid distal to the maternal zooid, or (much less often) by a distal kenozooid that has an encrusting base, including lateral walls with basal pore chambers from which the distal autozooids are budded. The ooecium in Atlantisina gen. nov. is also a kenozooid ( Fig. 1A ), but it is budded from a single large communication pore situated in the distal vertical wall of the maternal zooid ( Fig. 1B ). The pore is slightly raised relative to the remaining lateral communication pores and remains exposed above the frontal shield of the distal zooid throughout ontogeny. Formation of the ovicell may, therefore, not be restricted to the colony margin but may occur opportunistically at any stage during ontogeny whenever breeding conditions are optimal and eggs are fertilised. Owing to the elevated position of this pore the ooecial kenozooid is not in contact with the substratum and the basal ooecium is, if at all, barely touching the frontal shield(s) of subsequently budded distal zooid(s) ( Fig. 1A, C ). The ooecial kenozooid also lacks communication pores.

Thus, the Atlantisina gen. nov. ovicell differs structurally from the escharelliform ooecium present in the Romancheinidae sensu lato (see Ostrovsky 2013: 138). In the latter, the endooecium fuses with the frontal shield of the distal auto- or kenozooid, and the membranous ectooecium is continuous with the distal zooid’s membranous frontal wall. The ooecium structure in Atlantisina gen. nov., as well as in the other new genera introduced here, can be regarded as evolutionarily more primitive relative to the escharelliform ooecium (A.N. Ostrovsky, pers. comm. 2016). On the other hand, the kenozooidal nature of the ooecium, and its origin from a distinct ooecial pore in the maternal zooid’s distal wall, indicates a derived state within the Atlantisinidae .

The zooecium is divided into a variably sculptured, cryptocystal-type frontal shield and smooth gymnocystal calcification comprising the external lateral and distal vertical walls, including the distal part of the aperture, condyles, and oral spines ( Fig. 1 A–C). Moreover, the proximal margin of the aperture (i.e., the distal part of the umbonuloid frontal shield) is again composed of smooth gymnocyst, varying in extent from extremely narrow to extremely extensive when forming a suboral mucro ( Fig. 1 A–C). The interior-walled frontal shield and the gymnocystal lateral walls are separated by distinct sinusoidal sutures lateral to the orifice, leading in a bow to the proximal pair of spines and the condyles ( Fig. 1C ), where they meet (but do not fuse with) the gymnocystal calcification along the proximal aperture margin (which is again separated by a suture from the cryptocystal-type frontal shield along the proximal side of the mucro).

The usually extensively developed gymnocystal lateral walls are characteristic for Atlantisina gen. nov. species, comprising spacious basal pore chambers ( Fig. 1D ) with a single, large, external communication pore per neighbouring zooid, which is usually bounded by a distinct cryptocystal rim ( Fig. 1B ). In contrast, most Romancheinidae (e.g., Hemicyclopora Norman, 1894 ) have extremely reduced vertical walls with numerous small septula connecting the neighbouring zooids, and gymnocystal calcification is absent (e.g., Hayward & Ryland 1999). The morphology and formation of the frontal shield and orifice is, nevertheless, vaguely similar between Atlantisina and several romancheinid taxa such as Hemicyclopora , Escharella Gray, 1848 , and Escharoides Milne Edwards, 1836 . Moreover, in the latter genus communication between laterally neighbouring zooids also takes place via a single pore, whereas the distal wall comprises two or three basal pore chambers from which the distal autozooid is budded.

The respective number of oral spines in all Atlantisina gen. nov. species is, quite remarkably, extremely constant within and among colonies. Atlantisina meteor gen. et sp. nov. (see below) was the only species in which a deviation (by one spine) from the specific number of spines occurred among auto- or ovicelled zooids. Even in early astogenetic zooids, which are usually equipped with a higher number of spines than mature zooids in most cheilostomatid species, the specific number of spines is already present.

The simple, tatiform ancestrula ( Fig. 1E ) buds a single distal to lateral autozooid, followed by one to three distolateral zooids that are either situated around the ancestrula or form distal to the first-generation autozooid, apparently depending on microenvironmental clues. While there is also a single firstgeneration autozooid in Escharella , Hemicyclopora and Neolagenipora Vigneaux, 1949 , the ancestrula in Escharoides species usually produces two distolateral zooids (cf. Hayward & Ryland 1999). The ancestrula in Atlantisina gen. nov. also differs from the romancheinid taxa in having a distinctly more extensive opesia, with a constriction in the distal oral part, and in the absence of a crpytocyst.

Species of Atlantisina gen. nov. are presently restricted to bathyal depths along the NE Atlantic continental shelf, islands and seamounts. The northernmost distribution is along the northern Iberian margin (44° N) while Atlantisina gen. nov. was recorded as far west as Atlantis Smt (30° W) and south to the Canary Islands (28° N). No Recent species have been reported from the Mediterranean Sea but there is an early Pleistocene record from Sicily (A. Rosso, pers. comm. 2016).

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.