(Fig. 4 A–D)
Material examined. Parcel do Carpinteiro, Rio Grande do Sul, Brazil: Holotype: MNRJ- 1192, am 25 station 2, 32°09.173’S, 51 ° 28.099 ’W, 0 7 Aug 2009; Paratype: MNRJ- 1170, am 25 station 2, 32°09.173’S, 51 ° 28.099 ’W, 0 7 Aug 2009; MNRJ- 1171, am09 lance 6, 32° 17.032 ’S, 51 ° 48.754 ’W, 40 m depth, 28 September 2009; MNRJ- 1172, am 22 pc 1, 32° 13.716 ’S, 51 ° 46.101 ’W, 21 meters depth, 0 2 February 2009; MNRJ- 1169, am 21 P 1 Bento, 32 ° 16.674 ’S, 51 ° 47.330 ’W, 25 meters depth; MNRJ- 1191, am 24 station 2, 32°09.406’S, 51 ° 28.318 ’W, 31 July 2009; MNRJ- 1193, am 26 point 1, 32°08.348’S, 51 ° 27.589 ’W, 14 August 2009; MNRJ- 1194, am 28 point 2, 32°08.402’S, 51 ° 28.045 ’W, 28 August 2009; MNRJ- 1228, am 30 station 1, 32° 14.300 ’S, 51 ° 46.630 ’W, 25 meters depth; MNRJ- 1227, station 113 (Geo Costa I), 32 ° 15.900 ’S, 51 ° 46.970 ’W. Hermenegildo, Rio Grande do Sul, Brazil: MNRJ- 1195, HT#15, 33° 3.321 'S, 53 ° 13.824 'W, 13 meters depth, June 2011, Coll. FURG; MNRJ- 1196, HT#48, 33° 48.453 'S, 53 ° 12.857 'W, 21 meters depth, June 2011, Coll. FURG; MNRJ- 1197, HT# 48 b, 33 ° 48.453 ’S, 53 ° 12.857 ’W, 21 meters depth, June 2011, Coll. FURG; MNRJ- 1198, HT#22, 33° 44.213 ’S, 53 ° 14.414 ’W, 15.4 meters depth, June 2011, Coll. FURG; MNRJ- 1199, HT# 22 b, 33 ° 44.213 ’S, 53 ° 14.414 ’W, 15.4 meters depth, June 2011, Coll. FURG; MNRJ- 1200, HT#27, 33° 44.080 ’S, 53 ° 12.274 ’W, 19 meters depth, June 2011, Coll. FURG; MNRJ- 1258, H#20, 33° 41.254 ’S, 53 ° 10.116 ’W, 17 meters depth, June 2011, Coll. FURG; MNRJ- 1264, H#18, 33° 39.471 ’S, 53 °09.765’W, 14.7 meters depth, June 2011, Coll. FURG.
Diagnosis. Colony cylindrical, jointed and branching dichotomously; autozooids rhomboidal to hexagonal, orifice crescent-shaped with distal rim beaded and two prominent condyles rod-shaped, curved to the front. Avicularia replacing the autozooid with triangular mandible; oecium with circular aperture located above the zooidal orifice.
Description. Colony erect, cylindrical, branching dichotomously, jointed (Fig. 4 A). Only loose branches were collected. Autozooids rhomboidal to hexagonal (infertile: 337–425 (373) µm long x 200–250 (229) µm wide; fertile: 365–470 (403) µm long x 200–271 (231) µm wide), disposed in series (8-10) around the whole branch (Fig. 4 A–C). Orifice crescent-shaped without size difference between fertile and infertile zooids (59–80 (70) µm long x 100–137 (118) µm wide), proximal rim slightly convex with two prominent condyles rod-shaped, curved and directed to the front; distal rim with small bead. Cryptocyst granular, depressed. Gymnocyst thick, raised, granular like the cryptocyst (Fig. 4 B–D).
Avicularia almost the same length of the autozooids, narrower (317–388 (351) µm long x 147–188 (174) µm wide), may replace an autozooid; mandible triangular, palate with a large and shared pore at the proximal region, condiles not observed (Fig. 4 B–D).
Oecium immersed, aperture circular (30–71 (49) µm diameter), above the zooidal orifice (Fig. 4 C).
Etymology. The name riograndensis refers to the Rio Grande do Sul state, locality of the samples.
Geographic distribution. Rio Grande do Sul state (Parcel do Carpinteiro e Hermenegildo–present study).
Remarks. Almost 110 fossil and recent Cellaria species are described around the world. For the South Atlantic almost 20 species are recorded, being 17 recent and four fossils, coming mainly from Antarctic waters. Cellaria subtropicalis Vieira et al., 2010 and C. brasiliensis Winston et al., 2014 were the only species described from the Brazilian coast. Cellaria subtropicalis has hexagonal zooids, transversal oecium aperture and a rounded avicularium mandible. Cellaria brasiliensis is very similar to C. riograndensis n. sp. but it has shorter autozooids (324–414 (377) µm long), with different shape and a rounded distal end, slightly shorter orifice (90–126 (106) µm long) with proximal rim more developed and smooth frontal surface, avicularia with the same autozooid size, and rostrum with equilateral triangle-shaped.
Another similar species is C. louisorum Winston & Woollacott, 2009 described from West Atlantic (Barbados), but it differs from this species as it has a distinct orifice difference between infertile and fertile zooids (a wider orifice and a concave proximal rim in fertile zooids and a convex proximal rim in infertile ones), condyles of avicularia mandible well demarked, larger avicularia (382–455 (411) µm length), and a small rounded oecium foramen. Other species from South Atlantic have greater differences (larger zooids, series with different quantities of zooids, avicularia with semicircular mandibles, oecium with crescent orifice). Thus, we believe that this Cellaria is a new species.