Plesiocleidochasma arcuatum Ramalho & Moraes, 2021

Ramalho, Laís V., Moraes, Fernando C., Salgado, Leonardo T., Bastos, Alex C. & Moura, Rodrigo L., 2021, Bryozoa from the reefs off the Amazon River mouth: checklist, thirteen new species, and notes on their ecology and distribution, Zootaxa 4950 (1), pp. 1-45 : 20-22

publication ID

https://doi.org/ 10.11646/zootaxa.4950.1.1

publication LSID

lsid:zoobank.org:pub:B9578A01-9B27-40B9-BEF9-C6DEB714C652

DOI

https://doi.org/10.5281/zenodo.4663130

persistent identifier

https://treatment.plazi.org/id/6587D169-4862-4987-9E50-D3234698EB05

taxon LSID

lsid:zoobank.org:act:6587D169-4862-4987-9E50-D3234698EB05

treatment provided by

Plazi

scientific name

Plesiocleidochasma arcuatum Ramalho & Moraes
status

sp. nov.

Plesiocleidochasma arcuatum Ramalho & Moraes n. sp.

( Fig. 10 View FIGURE 10 )

Material examined. Holotype: MNRJBRY-1435: Brazil, Amapá state (Sta #3, 03°35.4267’N – 049°07.6028’W), 90 m, on rhodolith, 26 September 2014, collected by Fernando Moraes & Rodrigo Moura (NHo Cruzeiro do Sul ). GoogleMaps

Etymology. From the Latin (arcuatus, -a, -um) meaning arched, referring to the shape of the avicularium.

Diagnosis. Plesiocleidochasma having orifice with a transverse elliptical or sometimes broader V-shaped sinus, strong and blunt condyles and 3–5 spines. Single adventitious avicularium placed on a tumid cystid; rostrum triangular with tip curving downwards. Ovicell bearing a small central umbo.

Description. Colony encrusting, multiserial, unilaminar ( Fig. 10A View FIGURE 10 ). Autozooids polygonal, longer than wide [L 306–355–402 (SD 30, N 19); W 200–248– 319 µm (SD 25, N 20)], slightly inclined distally; frontal shield convex, smooth, with up to four small and rounded marginal areolar pores ( Fig. 10A–C View FIGURE 10 ). Orifice cleithridiate [L 87–96–106 (SD 6, N 9); W 68–79– 87 µm (SD 8, N 10)] with horseshoe-shaped anter and transversely elliptical or sometimes broader V-shaped sinus; condyles strong and blunt, somewhat curved and oriented proximo-medially; 3–5 distal oral spines (two in ovicellate zooids) that disappear later in ontogeny ( Fig. 10B–D View FIGURE 10 ). Orifice sometimes slightly obscured by a pair of umbones, developing on each side of the orifice, plus a third smaller umbo proximo-centrally placed below the orifice ( Fig. 10B, C View FIGURE 10 ). Single adventitious avicularium [L 70–77– 84 µm (SD 10, N 2)], absent in some zooids, laterally oriented, placed on a tumid cystid at about zooidal half length, marginal, budded from an areolar pore ( Fig. 10D View FIGURE 10 ); rostrum triangular, tip curving downwards (arched); palate with a triangular foramen and narrow crossbar, without columella ( Fig. 10D View FIGURE 10 ). Ovicell globular [L 139–155–172 (SD 14, N 4);W 157–213– 253 µm (SD 35, N 5)], usually depressed; ento- and ectooecium calcified, frontal labellum distinct, incised obliquo-laterally on both sides, trapezoidal in outline ( Fig. 10E View FIGURE 10 ); sometimes secondary calcification leaves visible only two circular pores at each side with a very thin horizontal slit between the pores ( Fig. 10C View FIGURE 10 ); ooecial surface smooth, bearing a small central umbo ( Fig. 10A, C, E View FIGURE 10 ).

Remarks. Two Plesiocleidochasma species have been recorded from Brazil: P. foliosum Winston, 2005 , from Rio de Janeiro state, and P. acuminata Ramalho et al., 2018 , from the Abrolhos Bank, Bahia state. The former species has orifice with smaller and rounded to arrow-shaped sinus, leaf-shaped frontal avicularia with four uncalcified windows on the palate, while the latter species has granular frontal shield, larger and pointed avicularia, and palate with four pores (three pores aligned transversely plus a fourth one above the median transverse pore line).

Plesiocleidochasma perspicum ( Hayward & Cook, 1983) from South Africa, is the most similar to the new species. They share the short oral umbones, the presence of a single avicularium on a tumid cystid and ovicell with distinct labellum and small median umbo. However, P. perspicum differs in having slender avicularium rostrum, a stout crossbar with a thickened and quadrate columella, plus an orifice with a distinctly V-shaped sinus. Plesiocleidochasma immersum ( Soule et al., 1991) from Thailand, also resembles the new species in having acute avicularium on a bulbous cystid and crossbar without columella, but it differs in having rounded and arcuated sinus, three oral spines, and an ovicell with horizontal slit placed frontally and above the ooecial aperture.

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