Biflustra sphinx

Description. Colony white, growing on hydroids, becoming erect, bilaminar. Autozooids subrectangular, 0.332 – 0.486 mm (0.382 ± 0.044) long and 0.210 – 0.327 mm (0.239 ± 0.037) wide, distal end rounded and proximal concave. Lateral walls thick, beaded narrow cryptocyst, without sharp denticles on proximal border. Short and thick gymnocystal tubercles with triangular bases often present in one or both outer proximal edges. Opesia occupying 75 – 90 % of zooid length, 0.295 – 0.375 mm (0.318 ± 0.027) long and 0.163 – 0.266 mm (0.190 ± 0.030) wide. Operculum with lightly sclerotized outer rim. Frontal membrane smooth, without spinules. Distal transverse walls with a row of uniporous mural septula, often with paired muscle scars set high; lateral transverse walls with two pairs of multiporous mural septula. Early astogeny unknown.

Diagnosis. Biflustra with encrusting colonies, multiserial, becoming erect and bilaminar; cryptocyst surrounding almost entire opesia length, shorter laterally than proximally, without denticles. Frontal membrane smooth. Distal transverse walls with a row of uniporous mural septula; lateral walls with two pairs of multiporous mural septula.

Remarks. There are some similarities in skeletal zooids of erect colonies of B. sphinx n. sp., B. arborescens and B. irregulata. Winston & Hayward (2012) characterized B. arborescens by having brown chitnous interzooidal lines, spinules on the frontal membrane, brownish opercula, and lack of open triangular tubercles in zooidal corners. These characteristics are also present in B. irregulata (see Seo & Min 2009; Taylor & Tan 2015), but they are not observed in B. sphinx n. sp. The skeletal zooids identified by Taylor & Tan (2015) as Acanthodesia cf. irregulata do not have soft parts, precluding the confirmation of presence of cuticular spinules. Skeletal zooids of B. sphinx n. sp. resemble those of Biflustra grandicella (Canu & Bassler, 1929) and Biflustra perambulata Louis & Menon, 2009 in having oval opesia and cryptocyst more developed proximally than laterally, without a median denticulate process such as described in B. marcusi n. sp. Biflustra sphinx n. sp. is distinct, however, in having shorter zooids (0.332 – 0.486 mm long in B. sphinx n. sp., 0.540 – 0.600 mm long in B. perambulata, and 0.620 – 0.960 mm long in B. grandicella) and gymnocystal tubercles with a triangular base, absent in both B. grandicella and B. perambulata. Gymnocystal tubercles were also illustrated in Flustra savartii Audouin, 1826 by Savigny (1817, pl. 10, fig. 2 b), but were not observed in Recent specimens from Egypt (see above). Specimens assigned to B. savartii from the Northern Bay of Safaga, Egypt (Ostrovsky et al. 2011, 2016) are also distinct in having multiporous mural septula in distal transverse walls.

Distribution. Brazil: Alagoas (Maceió). Biflustra sphinx n. sp. is often found growing on hydroids, becoming bilaminar.

Etymology. Epithet from the Greek Sphinx, female monster of Thebes who propounded riddles, in reference to the confusion in the genus Biflustra.

Material examined. Holotype: UFPE 0 55, Sobral sewer outfall, Maceió, Alagoas, Brazil, 9 º 40 ' 45 " S, 35 º 45 ' 01 " W, intertidal, erect colony on hydroids, coll. 21 October 2009 by L. M. Vieira & M. D. Correia. Paratype: UFBA 1599, same data as holotype.