Biflustra marcusi Vieira, Almeida & Winston, 2016, n. sp.

Biflustra marcusi n. sp.

(Figs. 12–14)

Acanthodesia savartii: Marcus, 1937: 40, pl. 7, figs. 16A–C. [Brazil: São Paulo] Non Flustra savartii Audouin, 1826. [Egypt]

Acanthodesia savartii: Marcus, 1938: pl. 14, fig. 36. [Brazil: São Paulo] Acanthodesia savartii: Marcus, 1941: 17, fig. 8. [Brazil: Paraná]

Acanthodesia savartii: Marcus, 1955: 280. [Brazil: Espírito Santo]

? Acanthodesia savartii: Osburn, 1940: 352, pl. 2, figs. 16–17. [Puerto Rico] Biflustra savartii: Vieira et al., 2008: 13. [Brazil: Espírito Santo, Rio de Janeiro, São Paulo and Paraná]

Material examined. Holotype: UFPE 0 91, Pratagy (Sereia), Maceió, Alagoas State, Brazil, 9º33'55" S, 35º38'40" W; intertidal, on algae, Sargassum spp., coll. 0 7 September 2007 by A.G.A. Borba Jr. Paratypes: UFBA 1597, UFPE 0 56, UFPE 0 57, same data as holotype. UFPE 0 59, Riacho Doce, Maceió, Alagoas, Brazil, 9º34'42" S, 35º39'19" W, intertidal, on algae, Sargassum spp., coll. 31 March 2007 by L.M. Vieira; UFBA 1599, Sobral sewer outfall, Maceió, Alagoas, Brazil, 9º40'45" S, 35º45'01" W, intertidal, erect colony on hydroids, coll. 21 October 2009 by L.M. Vieira & M.D. Correia. Additional specimens: UFPE 114, Jatiúca, Maceió, Alagoas, Brazil, 9º39'10" S, 35º41'40" W, intertidal, on algae, Sargassum spp., coll. 0 9 September 2003 by L.M. Vieira.

Diagnosis. Biflustra with encrusting colonies, unilaminar, multiserial, with cryptocyst surrounding almost entire opesia length, shorter laterally than proximally, with proximo-medial plate with triangular spines projecting into the opesia and two sharp curved denticles placed laterodistally at the cryptocyst. Distal transverse walls with a row of uniporous mural septula; lateral walls with two pairs of multiporous mural septula.

Description. Colony white, encrusting, unilaminar, multiserial. Zooids rectangular to hexagonal, 0.371–0.463 mm (0.424 ± 0.027) long and 0.235–0.346 mm (0.287 ± 0.027) wide, distal end rounded and proximal margins straight to concave. Lateral walls slightly raised and thin, without uncalcified bands; proximal corners often developed into raised and rounded gymnocystal tubercles with triangular bases. Cryptocyst surrounding almost all opesia length, shorter laterally than proximally; proximal cryptocyst slightly convex and granulose, a proximomedial plate with sharped triangular spines projecting into the membranous part of the frontal surface; two sharp and slightly curved denticles placed laterodistally, projecting obliquely toward to the midline of opesia. Opesia occupying about half of zooid length. Operculum with lightly sclerotized outer rim, 0.080–0.093 mm (0.086 ± 0.004) long and 0.099–0.117 mm (0.105 ± 0.006) wide. Distal transverse walls with a row of uniporous mural septula near to the basal wall; lateral transverse walls with two pairs of multiporous mural septula. Colonies formed by a twinned ancestrula.

Etymology. Named after Ernst Marcus (1893–1968), for his contributions to bryozoology.

Remarks. The type of Biflustra d’Orbigny, 1852, Biflustra ramosa d’Orbigny, 1852 (Grischenko et al. 2002: fig. 2; Tilbrook 2006: pl. 2A), has erect vincularian colonies and no ancestrula has been described or figured. There are, however, many interpretations for the usage of the genus Biflustra (e.g. Tilbrook 2006; Taylor & Tan 2015), with morphologically related species sometimes being assigned to distinct genera— e.g. Biflustra arborescens (Canu & Bassler, 1928b) and Acanthodesia irregulata (Liu, 1992) —due to the absence of information on ancestrula type. To avoid the usage of two generic names for morphologically related species, here we disagree with Taylor & Tan (2015) who assigned some species to the genus Acanthodesia Canu & Bassler, 1919 rather than Biflustra d’Orbigny, 1852 based on the presence of a twinned ancestrula and encrusting colonies. We believe that skeletal characters are useful to distinguish some problems in Membraniporidae, but due to the simplicity of external morphology, only a more complete knowledge of ancestrual formation and astogeny and/or results of molecular studies will clarify the use of Acanthodesia and Biflustra.

At least two species of Membraniporidae, Biflustra savartii (Audouin, 1826) and Biflustra tenuis (Desor, 1848) have been reported as widespread (e.g. Harmer 1926; Marcus 1937; Osburn 1940; Maturo 1957; Winston 1982; Winston 2005; Winston & Hayward, 2012). Some of these records, however, may also refer to different species, including Biflustra ramosa (d’Orbigny, 1852) (see Tilbrook 2006). The illustrations of Flustra savartii from Egypt (Savigny 1817: pl. 10, figs. 10.1, 10.2), type species of Acanthodesia, do not show the proximomedial denticle in the cryptocyst that is seen in syntype specimens of B. ramosa, type of Biflustra, and Biflustra crenulata (Okada, 1923). SEM images of putative B. savartii from the Northern Bay of Safaga (Ostrovsky et al. 2011, 2016), however, show autozooids without gymnocystal tubercles, and a short proximomedial cryptocystal denticle (present in some zooids). Biflustra marcusi n. sp. is distinguished from B. savartii, B. crenulata and B. ramosa, however, in having encrusting colonies; by the shape and size of the proximomedial denticle of cryptocyst, occupying 40–60% of the opesia width; and by the presence of two distolateral denticles directed medially to the opesia.

Marcus (1937) illustrated similar zooids in specimens reported as Acanthodesia tenuis (Marcus 1937: pl. 8, fig. 17B)—assigned to Biflustra denticulata (Busk, 1856) by Vieira et al. (2008), but identical to B. tenuis (sensu Winston & Hayward 2012, as Membranipora)—and A. savartii (sensu Marcus 1937: pl. 7, figs. 16A–C). Acanthodesia savartii sensu Marcus (1937) is here reassigned to B. marcusi n. sp. Rounded tubercles at proximal corners of zooids are often present in specimens of B. tenuis from Brazil, while these tubercles are often present in younger colonies of B. marcusi n. sp. from Alagoas. Specimens from Brazil of B. tenuis have cryptocyst with some denticles projecting into the opesia, without a proximomedial plate. In two other species reported from Brazil, B. arborescens and Biflustra paulensis (Marcus, 1937), the proximomedial cryptocystidial plate is absent. Specimens from Gulf of Mexico reported as A. savartii by Osburn (1940) resemble B. marcusi n. sp., being distinguished only by the absence of distolateral denticles directed toward the midline of the opesia; these specimens may be conspecific.

Specimens reported as Acanthodesia serrata Hincks, 1882 by Marcus (1937, p. 44, pl. 8, fig. 8) have developed cryptocyst, thus are distinct from Membranipora membranacea form serrata described by Hincks (1882) (= Membranipora villosa Hincks, 1880). Membranipora villosa is attributed to the Membranipora “membranacea-serrimella-villosa” morphs, known from NE Pacific (see Dick et al. 2005, p. 3692). Acanthodesia serrata studied by Marcus resembles those specimens figured by Hastings (1930, p. 707, pl. 4, figs. 13–15), but its identity remains uncertain. Specimens identified as Conopeum commensale Kirkpatrick & Metzelaar, 1922 by Marcus (1937) have spinules on frontal membrane, and they belong to B. arborescens.

Biflustra falsitenuis (Liu, 1992), described from China, also has a proximomedial cryptocystal plate with spines, but it is distinguished by having two large multiporous pore chambers in the transversal wall and in the absence of the two distal lateral denticles (see Liu et al. 2001: pl. 9, fig. 2), characteristic of B. marcusi n. sp.

Distribution. Biflustra marcusi n. sp. is often found encrusting algae. In Brazil, this species occurs at least from Alagoas to Paraná.