Reteporella obscura Denisenko 2022, n. sp.

Reteporella obscura n. sp.

(Fig. 2; Table 1)

Material examined. Holotype: ZIN1 /50742, one colony;Stn 2016_PA_2_151 (64.52786668° N, ˗ 54.7776999791463° W; 277 m; T 3.934 °C); collected by BEAMTRAWL, MT Paamiut, fish-shrimp trawl assessment survey. July 2016.

Paratype: ZIN 2 / 50747; colony fragment; Stn 2016_PA_1_16 (64.35196667° N; ˗ 53.8765166600545° W; 165 m; T 1.575 °C); collected by BEAMTRAWL, MT Paamiut, fish-shrimp trawl assessment survey. July 2016.

Diagnosis. Colony reticulate, broadly fan-shaped; fenestrulae large; different levels of granulation on frontal and abfrontal surfaces. Trabeculae of variable length, with 2‒3 series of alternating zooids, doubling at bifurcations. Zooids flat, with 3‒5 large marginal pores; marginal zooids near fenestrulae with 5‒6 marginal pores. Orifice semicircular, approximately as wide as long with rounded condyles and slightly prominent proximal edge; distal rim smooth with a well-developed row of denticles in its lower part. Spines paired, one on each side of orifice at about mid-length; peristome asymmetric with a widely open pseudosinus; larger lobe with a small circular avicularium directed terminally-proximally relative to the zooidal surface; rostrum finely toothed, crossbar complete, columella absent, cystid invisible, mandible edge raised. Frontal avicularia sporadic, oval and relatively small, crossbar complete, columella absent, palate forming a more or less developed shelf, distal uncalcified area semicircular. Abfrontal avicularia rare, circular, distal part raised with fine denticulation. Ovicells longer than wide with long fissure, and relatively narrow labellum.

Etymology. Latin “ obscura ” (unclear), alluding to the possibility of misidentification with closely related species of Reteporella.

Description. The colony is 40–50 mm high, broadly fan-shaped. The fenestrulae are mainly oval, twice as long as wide, commonly 1.1 x 0.53 mm (Fig. 2A, B; Table 1). The trabeculae (0.85 x 1.05 mm) consisting of two to three alternating, longitudinal series of autozooids, doubled at points of trabecular bifurcations (Fig. 2A). The abfrontal surface of the colony is densely and finely granulated, covered by flat kenozooids clearly delimited by vibices, and with rare round avicularia (Fig. 2B). One horn-shaped kenozooid (about 0.5 mm in length) with a rounded avicularium was observed (Fig. 2A, C, G). The granulation on the frontal side is comparatively coarser but less dense than that on the abfrontal surface (Fig. 2A, B).

Autozooids are elongate hexagonal, delimited by mainly straight edges, and occasionally by sutures, obscured by later calcification; autozooids size is about 0.49 x 0.275 mm, but width and length vary considerably especially in areas of bifurcation (Fig. 2D, J; Table 1). The autozooids have few (2–3) large, distinct marginal pores but zooids located near fenestrulae have an additional row of 5–6 pores near the external edge (Fig. 2D, J).

The primary orifice is semicircular with slightly prominent proximal edge, slightly wider than long (mean size 0.094 x 0.100 mm); the distal margin of the orifice is smooth along its upper edge and with well pronounced denticles along its lower margin; condyles are large and rounded. A pair of oral spines is present, one on each side of the orifice at about mid-length.

The peristome hides the orifice in frontal view and consists of two unequal lobes forming an open sinus (Fig. 2D–F). A single circular avicularium is present on its rim, mid-proximally, 0.041 mm long, proximally directed and oblique to the frontal surface (Fig. 2F).

The avicularium is immersed in the peristome, the avicularian cystid is invisible, and the distal rim of the mandible is finely toothed. Frontal avicularia are sporadic, oval (0.084 x 0.053 mm) demarcated by a raised rim (Fig. 2D, J); the distal margin of the rostrum is smooth, the mandible is semi-oval, the crossbar is complete without columella, and the distal uncalcified area is semicircular. Abfrontal avicularia are small, nearly circular (diameter 0.042 mm); the distal margin of the rostrum is toothed, the mandible is semicircular, and the crossbar is complete without columella.

Ovicells are located above the distal rim of the orifice; ooecia are longer than wide, with an elongate median fissure and a narrow squared labellum; ooecia become partly obscured by secondary calcification in late ontogeny (Fig. 2I).

Remarks. Reteporella obscura n. sp. was found in the sublittoral zone, at two stations in the Davis Strait of SW Greenland.At first glance, the new species is very similar to R. beaniana, which is widely distributed in the Arctic Atlantic, in the appearance of colonies and zooids, in the morphology of the secondary orifice and peristome with widely open pseudosinus, and in having a pair of orificial spines. However, the new species is distinguishable from R. beaniana in having a distinct granulation on both surfaces of the colony, and in the shape of the primary orifice which is bell-shaped in R. beaniana and semicircular in R. obscura n. sp. Differences are also observed in the shape of the condyles, which are roundish in the new species and rounded triangular in R. beaniana (Hayward & Ryland 1996, 1999). The suboral avicularium of the new species is round with an indistinct cystid, whereas in R. beaniana it is oval and the cystid is prominently emerging above the frontal shield. In addition, Reteporella obscura n. sp. is characterized by globular ovicells, longer than wide with a prominent but relatively narrow labellum, whereas R. beaniana has ovicells that are wider than long, and with an arched aperture, and a flattened frontal surface (Hayward & Ryland 1996, 1999).

Distribution. Lower sublittoral zone (165–277 m), Davis Strait (SW of Greenland).