Glabrilaria polita Rosso, 2018

Rosso, A., Beuck, L., Vertino, A., Sanfilippo, R. & Freiwald, A., 2018, Cribrilinids (Bryozoa, Cheilostomata) associated with deep-water coral habitats at the Great Bahama Bank slope (NW Atlantic), with description of new taxa, Zootaxa 4524 (4), pp. 401-439 : 417-419

Glabrilaria polita Rosso n. sp.

(Figs 39–45; Tables 1, 2)

Material examined. Holotype: Great Bahama Bank slope, R/ V Maria S. Merian Cruise MSM20 /4, Station GeoB16375-1 (one colony portion, encrusting a crustacean fragment including living zooids, ovicellate and nonovicellate)—SMF-45.514.

Etymology. From the Latin, politus, alluding to the smooth and elegant appearance of the frontal shield.

Description. Colony encrusting (Fig. 39), unilaminar, apparently forming pauciserial lobes.

Zooids small, oval but usually with an elongate proximal tip, often deeply wedged within proximal zooids (Figs 40–42), moderately convex and distinct, the boundaries marked by furrows. Gymnocyst very narrow, except for the proximal and occasional lateral extensions, moderately inclined (Fig. 41). Communication through basal pore-chambers and via several minute round communication pores visible along lateral walls (Fig. 43). Frontal shield oval, occupying almost all the zooidal surface, usually formed by 16–17 wedge-shaped costae, converging towards a median, non-carinate zigzag-like suture (Fig. 41). Costae gently swelling and smooth (Fig. 45), joined by five, rarely six bridges separated by regularly spaced, about 4–8 µm wide, round to kidney-shaped intercostal pores, giving the general appearance of a concentric net (Figs 41, 42). Only 3–4 intercostal spaces are present proximally to the suboral pair of costae (Fig. 43), which are broader and form a semi-elliptical to subtriangular smooth shelf at level with the frontal surface, bearing two pores along the midline but at some distance from the orifice, the proximal one usually larger (Figs 41, 42). Roundish papilla pores between bases of subsequent costae, barely protruding and level with the costae. Orifice transversely D-shaped, with a straight proximal border, wider than long (the maximal width reached at about mid-length, the proximal border usually narrower), distally surrounded by five, equally spaced, spine bases (Fig. 45), the proximal pair originating at some distance from the proximal border of the orifice; four spines persisting in ovicellate zooids, the distal ones erect at a straight angle to the frontal surface, partly encircled by the ooecium (Fig. 43).

Ovicells hyperstomial, cleithral. Ooecium formed by the distal kenozooid with 3–4 smooth costae, visible in the frontal view [type 1 sensu Ostrovsky (1998, 2008, 2013) and type B sensu Bishop & Househam (1987)]. Ectooecium smooth, with a longitudinal median suture, about as long as wide (Figs 41–43).

Avicularia adventitious, of two types: 1) pedunculate, with trumpet-shaped cystid with a narrow base, a triangular rostrum occupying almost half length, an elongated triangular mandible, and ill-defined pivotal denticles; sparse, originating from basal pore-chambers along distolateral zooidal walls (Figs 41, 42, 44, 45); 2) semi-erect, associated with ovicellate zooids, lining on the lateral sides of ectooecium, originating from the basal pore-chambers in distolateral zooidal walls at some distance from the orificial spines, single or paired, distally directed, elongated triangular, with ill-defined condyles and an elongated parallel-sided gently serrate rostrum (Figs 41, 43).

Kenozooids relatively numerous, bounding colony margins (Figs 39, 40); often irregularly shaped and sized, but small in comparison to zooids and less elevated. They have an extensive gymnocyst and a cribrimorph shield of 4–8 costae in a radiating pattern.

Ancestrula not observed.

Remarks. Glabrilaria polita Rosso n. sp. has very distinctive characters that enable its allocation within the genus Glabrilaria (see above), but also ensures its distinction from congeners living in the same region and elsewhere. Glabrilaria polita Rosso n. sp. is superficially similar to G. hirsuta Rosso n. sp. and hardly distinguishable from worn colonies of this species under steremicroscope at a rapid examination. However, G. hirsuta Rosso n. sp. has a prickly appearance, slightly smaller costate shields, slightly shorter but slightly wider zooids (essentially caused by the different development of the lateral gymnocyst), smaller zooidal orifices, larger ooecia with a transversal spiny crest, and smaller stalked avicularia. Glabrilaria hirsuta Rosso n. sp. also lacks the semi-erect avicularia associated with ovicells.

Glabrilaria polita Rosso n. sp. is especially similar to G. orientalis (as Puellina ), a species erected by Harmelin (1988) for a cline of closely allied morphotypes that he treated as subspecies, namely G. orientalis orientalis , G. orientalis lusitanica , and G. orientalis azorensis , all distributed in the Atlantic-Mediterranean area. All of them are characterised (Harmelin 1988, figs 12, 13, 17d–l; Rosso et al. 2018, fig. 5h–i) by a faintly ornamented ooecium with a median prominent longitudinal carina, and by two articulated oral spines and one semierect avicularium on each side, both spines and avicularia variably lined on it and avicularian rostra often converging distally. However, in Harmelin’s taxa avicularia associated with ovicells originate close to the oral spines. Furthermore, the zooids have shields formed by a lower number of costae that are variably carinate, especially the suboral ones, which fuse forming a suboral area with upward projecting crests, and a central suture leaving no pores, or only one pore in G. orientalis azorensis . The orifice shows six or seven oral spines. Pedunculate avicularia are present in all these species.

The occurrence of relatively large, paired, semi-erect avicularia is shared also with Cribrilaria biavicularia Kataoka, 1961 described from the Pleistocene of Japan, a species that has been later recorded as Puellina (Cribrilaria) biavicularia from the present-day Kermadec Ridge, between 130–630 m by Gordon (1984: 63, fig. 21A). In this species, however, pedunculate avicularia are larger and constantly associated also with non-ovicellate zooids, located distolaterally to zooidal orifice and slightly convergent distally. Apart of the ovicellate zooids, additional semi-erect avicularia of comparable size and shape, originate also from pore-chambers of sparse kenozooids. Harmelin (1988) proposed to consider comparable semi-erect avicularia of G. orientalis as having evolved from columnar ones. Following Harmelin’s opinion and taking into consideration that the occurrence of pedunculate adventitious avicularia is diagnostic of the genus Glabrilaria , this species, presently accepted as Cribrilaria biavicularia (WoRMS register of marine species: http://marinespecies.org/aphia.php?p=taxdetails&id=736682, accessed 7 March 2018), should be allocated in Glabrilaria .

Avicularia associated with ooecia are also present in G. africana Hayward & Cook, 1983 and have been sometimes figured also in “ Puellina ” harmeri Ristedt, 1985, a shallow-water Indo-West Pacific species (e.g. Dick & Grishenko 2016; Yang et al. 2018). However, in this latter species, which has seven oral spines and tuberculate costae, adventitious avicularia are inconstant and sometimes associated with the orifice of non-ovicellate zooids. Furthermore, interzooidal avicularia also occur, especially at the colony periphery. For the concomitant presence of both interzooidal and adventitious avicularia the generic allocation of this species is puzzling, but it could be better included in Cribrilaria rather than in Puellina , as first suggested by Ristedt (1985). Interestingly, this species shows a mixture of characters also in relation to the ovicell. As remarked by Ristedt (1985), its ooecia of the type 1 sensu Ostrovsky (1998, 2008, 2013), are either produced by a distal autozooid or by a kenozooid (visible or not in frontal view), thus falling within the A or B type of Bishop & Househam (1987).

Distribution. Glabrilaria polita Rosso n. sp. is known from a single colony collected at 677 m depth on the GBBS, in sediments rich in deep-water coral fragments.