Plesiocleidochasma acuminata, Ramalho & Taylor & Moraes & Moura & Amado-Filho & Bastos, 2018

Ramalho, Laís V., Taylor, Paul D., Moraes, Fernando Coreixas, Moura, Rodrigo, Amado-Filho, Gilberto M. & Bastos, Alex C., 2018, Bryozoan framework composition in the oddly shaped reefs from Abrolhos Bank, Brazil, southwestern Atlantic: taxonomy and ecology, Zootaxa 4483 (1), pp. 155-186 : 176-177

Plesiocleidochasma acuminata n. sp.

( Fig. 6B, C )

? Hippoporina porcellana: Braga, 1967: 12 , fig. 7, 8.? Plesiocleidochasma porcellanum: Almeida et al., 2015a: 5 . Plesiocleidochasma sp. nov.: Bastos et al., 2018: table 1.

Material examined. Abrolhos Bank, Bahia State, Brazil: Holotype: MNRJ-Bry1381, Parcel dos Abrolhos, 15 m depth, February 2014, col. R. Moura, G. Amado-Filho & A. Bastos.

Etymology. From the Latin ‘ acuminatus, -a, -um ’, meaning ‘sharp, pointed’, referring to the conical shape of the frontal avicularium.

Diagnosis. Colony encrusting. Autozooids polygonal with finely granular frontal shield, sometimes with an umbo present in the median region and/or at the zooidal corners. Cleithridiate orifice with a broad and shallow sinus; avicularium single, frontal, large, rostrum elongate triangular with a thin and sharp tip, palate with three aligned pores plus an additional pore distal to these three.

Description. Colony encrusting, multilamellar. Autozooids polygonal, slightly longer than wide (377–431– 467 µm long x 325–408–473 µm wide), disposed in quincunx ( Fig. 6B ); frontal shield finely granular, imperforate except for a few scattered circular areolar pores (2–5 in each zooid); an umbo sometimes developed in the median region and/or at the proximal and distal corners of the zooid ( Fig. 6C ). Orifice cleithridiate, keyhole-shaped, longer than wide (133–147–157 µm long), anter with smooth rim, circular to oval, (95–105–113 µm wide), poster formed by a semicircular, broad and shallow sinus (54–63–71 µm wide); condyles prominent, curved downwards ( Fig. 6C ). Usually one large avicularium (145–175–205 µm long) on each autozooid, located laterally and below the orificial sinus; rostrum triangular, tip elongate, thin and sharp, embedded in frontal shield calcification; palate with four pores, three aligned plus a fourth above the median pore ( Fig. 6C ). Ovicell not observed.

Geographic distribution. Abrolhos Bank, Bahia State ( Bastos et al. 2018; present study).

Remarks. Two Plesiocleidochasma species were previously recorded in Brazil: P. cleidostomum (Smitt, 1973) and P. porcellanum ( Busk, 1860) ( Vieira et al. 2008, as Schedocleidochasma porcellanum ; Almeida et al. 2015a). However, Winston (2005, 2016) when redescribing P. cleidostomum (Smitt, 1973) excluded records of this species from the Brazilian coast, mentioning that it belongs to the complex ‘ cleidostomum ’ but differs in having striated ooecia and more distolaterally directed avicularia. Plesiocleidochasma porcellanum has been reported to occur in several parts of Brazil (Rocas Atoll – Rio Grande do Norte, Espírito Santo, Rio de Janeiro, and São Paulo states – see Vieira et al. 2008 – and Abrolhos Bank – Almeida et al. 2015a). Moreover, Berning (2012) stated that this species is actually a species complex and all records, except for those from the Madeiran Archipelago, should be questioned. Winston et al. (2014) also mentioned that some specimens assigned to P. porcellanum and P. cleidostomum from NE and SE Brazil may represent undescribed species.

The species identified as P. porcellanum by Marcus (1937) from São Paulo State differs from P. acuminata n. sp. as it has an orifice with an anter as wide as the poster, and narrower avicularia. Specimens recorded from Rio de Janeiro State by Braga (1967) are more similar but the description does not mention the pores on the avicularian palate, precluding the confirmation of this identification. The Brazilian species P. foliosum Winston et al., 2014 , described from Rio de Janeiro State, differs from the Abrolhos specimen in: the smaller (117–144 µm long), leafshaped avicularia with three unaligned pores plus a fourth pore above them on the palate; orifice with a small rounded to arrow-shaped sinus; and only a central umbo. The Abrolhos specimen may be distinguished from P. porcellanum as it has a broader orifice (poster 104–121 µm wide, anter 62–80 µm wide), and a smaller (78–92 µm long) triangular avicularium with a semicircular to triangular non-calcified palate. Plesiocleidochasma cleidostomum has a short orifice (108–126 µm long), a smaller avicularium (108–144 µm long) that is raised from the frontal shield usually on an umbo, and a trifoliate palate. The morphological closest species is P. normani (Livingstone, 1926) , from the Indo-Pacific, which has a similar avicularium with an acuminate tip and three aligned pores on the palate, but P. normani can be distinguished by its larger autozooids (450–495–540 µm long x 310–365–420 µm wide), larger and more rounded aperture (150–165–180 µm long x 130–145–160 µm wide) and larger avicularia (230–245–270 µm long). Plesiocleidochasma fallax ( Canu & Bassler, 1929) , from the Philippines, also has four pores on the palate, but a large leaf-shaped avicularium without an elongated tip, a wider orifice and frontal shields without umbos or protuberances.

Figures

FIGURE 6. Scanning electron micrographs of three bryozoan species. A. Gemelliporina glabra, fragment showing orifices and a small avicularium. B, C. Plesiocleidochasma acuminata n. sp. B. General view of a fragment showing infertile zooids. C. Detail of some zooids showing cleithridiate orifices, a few scattered areolar pores and acuminate avicularia with rostra ending in a sharp and elongate tip. D–F. Rhynchozoon aff. rostratum. D. General view of a colony part showing some zooids with peristomial tubercles and frontal avicularia. E. Detail of some autozooids showing peristomial tubercles and frontal, triangular avicularia. F. Detail of one zooid showing distally beaded orifice and a suboral lateral avicularium with a triangular rostrum, and a suboral umbo.