Arachnopusia haywardi, Vieira, Leandro M., Gordon, Dennis P., Souza, Facelucia B. C. & Haddad, Maria Angélica, 2010

Vieira, Leandro M., Gordon, Dennis P., Souza, Facelucia B. C. & Haddad, Maria Angélica, 2010, New and little-known cheilostomatous Bryozoa from the south and southeastern Brazilian continental shelf and slope, Zootaxa 2722, pp. 1-53 : 18-20

Arachnopusia haywardi n. sp.

( Figures 30–39 , Table 8 )

Material examined. Holotype. MZUSP 0 322, Brazil, project REVIZEE South SCORE, RV ‘Prof. Wladimir Besnard’, station 6658. Additional material. MZUSP 0 343, Brazil, project REVIZEE South SCORE, RV ‘Prof. Wladimir Besnard’, station 6678.

Diagnosis. Colony forming unilaminar sheets, with oval autozooids; frontal shield with 6–16 irregular ligulate pores; primary orifice subquadrangular with single distolateral spine; peristome subquadrangular, becoming more or less crescentic in later ontogeny; 1–5 peristomial avicularia ; larger triangular avicularia sometimes developed on proximal margin of autozooid.

Etymology. The name honours bryozoologist Peter J. Hayward in recognition of his many studies on bryozoan taxonomy, in particular of Arachnopusia species.

Description. Colony encrusting, forming unilaminar sheets. Autozooids broad, oval, convex, distinct at growing edges. Frontal shield thickly calcified, with 6–13 large irregular pores, each with 1–2 ligulae, most conspicuous in zooids nearer colony margin; in later ontogeny, frontal shield with 7–16 deep pores. Orifice subquadrangular; peristome more or less rounded and wider; orifice somewhat more arcuate in later ontogeny. A single distolateral spine present, becoming long in later ontogeny. One small proximal avicularium often present, subtriangular, smooth rostrum distally directed, perpendicular to frontal plane, without crossbar; rarely 1–2 smaller lateral-oral avicularia , smooth rostrum medially directed, without crossbar. Some zooids with 1–2 small avicularia on distal rim of peristome; smooth rostrum directed proximally or proximolaterally, without crossbar. Other small triangular avicularia sporadically present on frontal shield or ooecia. Larger triangular avicularia may be developed on proximal margin of autozooid; rostrum proximally directed. Ovicell subglobular, recumbent, the surface with thin secondary calcification, with a narrow transverse band of granular entooecium exposed frontally.

Remarks. Arachnopusia haywardi n. sp. is the most distinctive species of the genus in our samples, which included other species hitherto unknown on the Brazilian coast, such as Arachnopusia monoceros ( Busk, 1854) (MZUSP 0309), and at least two other undentified species. Only A. pusae Marcus, 1955 was previously recorded from Brazilian waters. Arachnopusia haywardi is distinguished by the presence of 6–16 ligulate pores and a subquadrangular orifice with a single distolateral spine and some peristomial avicularia ; the proximal apertural avicularium with distally directed rostrum is always present.

Hayward and Thorpe (1988) recorded 18 species of Arachnopusia Jullien, 1888 from Antarctic, subantarctic and some southern cold-temperate localities, showing a high diversity of the genus in South Atlantic Ocean. They commented on the need for further studies of Arachnopusia species from South America in order to understand patterns of distribution and biodiversity in the genus. Among species recorded by Hayward and Thorpe (1988), A. monoceros has its distribution expanding to south of Brazil (MZUSP 0309); this species is characterized by unilaminar colonies, small autozooids with 9–20 rounded ligulate foramina, a quadrangular aperture with a single median avicularium and ovicells with a wide band of exposed entooecium.

Arachnopusia haywardi has smaller zooids than some of those previously recorded from South Atlantic Ocean; however, the autozooid has a similar size to those found in at least in six species — Arachnopusia decipiens Hayward & Thorpe, 1988 , A. discors Hayward & Thorpe, 1988 , A. globosa Hayward & Thorpe, 1988 , A. perforata ( Maplestone, 1909) , A. tristanensis Hayward & Thorpe, 1988 and A. valligera Hayward & Thorpe, 1988 . Among these species, A. decipiens forms bilaminar sheets and zooids have 5–8 ligulate foramina, four short thick spines (only 1–2 in later ontogeny) and ovicells with 3–4 short columnar avicularia . Hayward and Thorpe (1988) recorded six species with more than 16 frontal foramina, viz. A. discors , A. ferox Hayward & Thorpe, 1988 , A. globosa , A. perforata , A. triarmata Hayward & Thorpe, 1988 and A. tubula Hayward & Thorpe, 1988 .

Six species have larger zooids than A. haywardi — A. aquilina Moyano, 1970 , A. gigantea ( Kluge, 1914) , A. inchoata Hayward & Thorpe, 1988 , A. latiavicularis Moyano, 1970 , A. triarmata and A. tubula . Bilaminar A. gigantea has a frontal shield with only short lobes of frontal shield projecting from the zooidal margins. The South American species A. admiranda Moyano, 1982 is distinguished by the well-developed proximal rim of the orifice and large lateral-oral avicularia . The number of frontal foramina in A. aquilina is about 10– 14, deeper and unequally sized and without ligulae, which are conspicuous in A. haywardi . Arachnopusia valligera grows as unilaminar colonies. Its autozooids measure about 0.50 mm in length with 8–11 irregularly sized foramina with narrow ligulae. It differs from A. haywardi in having a narrower apertural plate about 0.13 mm wide.

Distribution. Brazil: off São Paulo state, 99–157 m (present study).

Figures

FIGURES 28 – 33. 28 – 29, Chorizopora brongniartii (Audouin, 1826), MZUSP 0 302, off São Paulo, Brazil, on Hippomenella amaralae n. sp. 28, Colony; 29, close-up of ovicelled zooid. 30 – 33, Arachnopusia haywardi n. sp. in later ontegeny, MZUSP 0 322 (part of the paratype specimen), off São Paulo, Brazil. 30, Colony; 31, close-up of autozooid; 32, frontal view of oral region; 33, close-up of aperture.

FIGURES 34 – 39. Arachnopusia haywardi n. sp., MZUSP 0 322 (holotype specimen), off São Paulo, Brazil. 34, Colony; 35, close-up of colony with some autozooids; 36, close-up of colony with some autozooids and three ovicells; 37, closeup of autozooids and a large frontal avicularium; 38, close-up of ovicelled zooid; 39, close-up of orifice with single latera spine.

Tables

TABLE 8. Measurements (in mm) of Arachnopusia haywardi n. sp.

	n min–max	mean	SD
Autozooid length	15 0.467–0.813	0.646	0.092
Autozooid width	15 0.371–0.593	0.477	0.092
Primary orifice length	6 0.153–0.173	0.166	0.007
Primary orifice width	6 0.167–0.187	0.170	0.007
Secondary orifice length	12 0.133–0.187	0.161	0.016
Secondary orifice width	12 0.200–0.267	0.236	0.019
Ovicell length	3 0.220–0.247	0.233	0.011
Ovicell width	3 0.247–0.267	0.253	0.009