Reteporella vitta Denisenko 2022, n. sp.

Reteporella vitta n. sp.

(Figs 3, 4; Table 2)

Material examined. Holotype: ZIN 1 /50743, one colony; Stn 2016_PA_5_58 (64.8872833251953° N, ˗ 34.5760166803996° W; 948 m; T 3.24 °C); collected by Alfredo III trawl, MT Paamiut, fish-shrimp trawl assessment survey. July 2016.

Diagnosis. Reteporella with delicate, reticulate colony, large fenestrulae and dimpled frontal and abfrontal surfaces. Trabeculae long, consisting of one to three alternating series of autozooids without doubling at bifurcations. Autozooids with 1‒3 large marginal pores and with wavy edges; primary orifice semicircular, slightly wider than long; condyles large, robust, trapezoidal; spines absent; peristome intermediately tall, consisting of two unequal lobes, often closed forming a roundish spiramen. Circular suboral avicularium with prominent chamber located on larger peristomial lobe; distal rostrum finely denticulate or smooth, crossbar complete, columella absent, palate narrow; frontal avicularia oval with complete crossbar, no columella and narrow palate. Abfrontal avicularia nearly circular, distal rostral margin denticulate, without palate. Ovicells prominent, sometimes with a short labellum and with closed fissure in late ontogeny.

Etymology. Latin “ vitta ” (lacy), alluding to the delicate, graceful, lacy appearance of the colony.

Description. The colony is reticulate, delicate and shiny. The frontal sides of the autozooids face towards the inner side of the rosette, as it is common in Reteporella species. As the colony grows, it develops as asymmetrical lateral lobes that curl outwards and backwards, transforming the colony into a funnel, in which, once the lobes come into contact with each other, the abfrontal side becomes the inner surface of the funnel, and the frontal side its outer surface (Fig. 3A, B). The colony is up to 60 x 25 mm in size; the fenestrulae are large, elongate, rhomboidal, polygonal or oval; their length (1.9‒2.4 mm) is twice their width (0.7‒1.05 mm).

Both surfaces of the colony (i.e. zooidal frontal shield and the abfrontal surface) are regularly and densely covered by polygonal depressions marked by thin ridges. The abfrontal side is covered with kenozooids delimited by clearly visible vibices. The trabeculae are long (0.6–1.9 mm) and narrow (0.24–0.65), consisting of 1–3 alternating longitudinal series of autozooids (Fig. 4A, B).

Autozooids are elongate, hexagonal; the frontal shield is shiny and slightly convex with wavy edges delimited by sutures, somewhat blurred in zooids with ovicells (Fig. 4D, E). Autozooids vary considerably in size (Table 2) but they are usually about 0.75–0.85 mm long by about 0.25 mm wide. The dimpled frontal surface bears usually 1‒2 large marginal pores, with or without a low rim.

The primary orifice, partly hidden by the peristome, is semicircular, slightly wider (0.12 mm) than long (0.08 mm) (Fig. 4C, D); the proximal edge is straight, the distal margin is smooth along its upper edge, but has a slightly immersed row of minute blunt denticles better pronounced in ovicell-bearing zooids. The condyles are large, blunt, trapezoidal (Fig. 4C), deeply immersed and poorly visible when viewed using a stereomicroscope. Oral spines were not observed in the analyzed specimen.

The peristome hides half of the orifice and consists of two unequal lobes, open or closed, forming in the latter case a small spiramen (Fig. 4C, D), which often disappears due to progressing calcification, regardless of the location of the zooid in the colony.

On the larger peristomial lobe there is a small, rounded (Fig. 4C, D) suboral avicularium (about 0.047 mm in diameter) with a toothed distal rostrum, complete crossbar without columella, the palate as a narrow shelf, and semicircular mandible (Fig. 4D–F). The suboral avicularium is generally oriented proximally and obliquely to the colony surface, and its cystid protrudes noticeably. Frontal avicularia are also small, although slightly larger than the suboral ones, oval, 0.083 x 0.056 mm, parallel to the frontal surface, with smooth rostrum and complete crossbar, palate as a narrow shelf, uncalcified semicircular area proximal to the crossbar often larger than the distal semi-elliptical one, and semicircular mandible (Fig. 4E). Abfrontal avicularia (Fig. 4B) are small, nearly circular (diameter 0.042 mm), with the distal margin of the rostrum toothed, complete crossbar without columella, and semicircular mandible (Fig. 4G).

The ovicell is prominent, the length (0.235 mm) slightly greater than the width (0.228 mm), its proximal surface is slightly flattened, sometimes with a short, weak labellum, but the labellum is usually lacking. The median fissure closes during ovicell formation, leaving in its place a long, narrow median depression in the proximal half of the ooecium (Fig. 4D, E).

Remarks. Despite the large volume of material processed, the new species R. vitta n. sp. was found only in one sample. The new species has a dimpled surface as R. watersi and R. rara from the North Atlantic, but in contrast to these species, which have robust colonies and a dull surface (Jullien & Calvet 1903; Hayward 1994; Hayward & Ryland 1996, 1999), the colony of R. vitta n. sp. is delicate, shiny and with large fenestrulae. Based on the descriptions by Hayward & Ryland (1996, 1999) and Jullien & Calvet (1903), the fenestrulae in R. vitta n. sp. are 2.3 times larger than those in R. watersi and R. rara.

The arrangement of autozooids within the colony also differs among these species. In R. vitta n. sp., autozooids form a series of 1–3 rows, remaining constant in width at bifurcations, whereas there are 3–5 rows of autozooids in R. watersi that double in number at bifurcations.

Reteporella vitta n. sp. also differs from R. watersi and R. rara in the size of autozooids (see Tables 3, 4). For instance, the autozooids in R. vitta n. sp. are 1.5 times longer than in R. watersi and R.rara. The primary orifice in all three species is wider than long, but the proportions are different with the primary orifice of R. vitta n. sp. and R. watersi smaller than that of R. rara (c. 0.137 x 0.2 mm; B. Berning, pers. comm. 2022), in which the proximal edge is slightly more convex than in the new species. The morphology of the condyles differs as well among the three species.

Moreover, although all species have a small suboral avicularium, it is oval in R. watersi and in R. rara, and round in R. vitta n. sp. The orientation of the peristomial avicularium is also different in the species under consideration; in R. vitta n. sp. and R. rara, it is oriented terminally to the autozooidal surface, while in R. watersi, the rostrum is nearly parallel to the frontal autozooidal surface. The location of the suboral avicularium within the peristome also differs in these species. In R. watersi and R. rara the avicularian chamber is not visible, but in R. vitta n. sp. it is prominent and clearly raised above the frontal autozooidal surface.

The ooecium of R. watersi has an open elongate fissure and a conspicuous labellum, whereas in R. vitta n. sp. the fissure is closed and the labellum is small or absent. In R. vitta n. sp., the ectooecium closes immediately as the ooecium forms, and only an elongate, droplet-shaped depression resembling a fissure is evident on the surface. The ooecium in R. watersi has a conspicuous labellum, whereas in R. vitta n. sp. the labellum is small or absent.

Distribution. Upper continental slope of SE Greenland.