Arachnopusia discors Hayward and Thorpe, 1988

Hayward, Peter J. & Winston, Judith E., 2011, Bryozoa collected by the United States Antarctic Research Program: new taxa and new records, Journal of Natural History 45 (37 - 38), pp. 2259-2338 : 2291-2294

Arachnopusia discors Hayward and Thorpe, 1988

( Figure 15 )

Arachnopusia discors Hayward and Thorpe, 1988b: 784 , fig. 3C, D.

Material

Hero cruise 693 station ( SOSC 10 ), 54 ◦ 39’ S, 64 ◦ 22’ W, 46 m, 31 July 1969; one colony encrusted on Smittina smittiana ( Busk, 1884) .

Description

Colony encrusting, unilaminar. Autozooids oval to hexagonal, convex, separated by distinct grooves; 0.75–1.00 by 0.38–0.6 mm. Frontal shield with 20 to 30 small foramina, irregularly oval, many with a short ligula and appearing reniform. Aperture wider than long, bounded by a low peristome, peaked medio-proximally where it bears a single avicularium, and forming a low, continuous ridge across the frontal surface of the ovicell. Apertural plate ( Figure 15B ) about as wide as long, shallowly concave, with a pronounced lip on the distal and lateral edges which becomes coarsely rugose in later ontogeny. Two distal oral spines and a single lateral oral spine present, the distal pair indistinct, apparent in earliest ontogeny but obscured by development of peristome, only the lateral oral spine persisting. A small avicularium present in the proximo-lateral corner of the aperture, opposite to the single spine, directed proximally, with the plane of the rostrum perpendicular to the apertural plane; a second avicularium situated immediately lateral to the spine, its rostrum normal to the frontal plane, directed proximo-laterally. Ovicell about as wide as long, with a narrow band of smooth entooecium bordering its aperture; a peristomial ridge crosses the ovicell in early ontogeny, and it is then soon obscured by a thickening ooecial cover. Additional small avicularia develop on the peristomial ridge, up to three in total, with variable orientation; rostrum narrowly triangular, 0.10 mm long, crossbar incomplete, palate lacking. Interzooidal avicularia, up to 0.25 mm long, develop sporadically along edges of autozooids, with elongate, bluntly triangular rostrum, thin, incomplete crossbar and without a palate. Large vicarious avicularia present at one point on the colony margin ( Figure 15C ): the cystids are as large as autozooids, with rostra, c. 0.30 mm long, acute to frontal plane, directed at colony periphery and supporting a broadly triangular mandible.

Remarks

Arachnopusia discors was described by Hayward and Thorpe (1988b) from a single station off Cape Horn (56 ◦ 19.5’S, 67 ◦ 09.15’ W, 121 m), and this present record, from the same region of the southwest Atlantic, marks only the second occurrence of the species. It is especially characterized by its frontal shield, with 20 to 30 small, ligulate foramina, and the broad, shallowly concave apertural plate, which has coarse granulations distally, and these features are well shown in the new material. The medio-proximal peristomial avicularium and the two lateral oral avicularia are also present in both the holotype and the specimen described here, but the large vicarious avicularia were not noted in the original description .

Superfamily LEPRALIELLOIDEA Vigneaux, 1949 Family ROMANCHEINIDAE Jullien, 1888

Lageneschara peristomata sp. nov.

( Figure 16 )

Material

Holotype. NMNH 1154042 : Eltanin cruise 22, station 1595, 54 ◦ 40’ to 54 ◦ 39’ S, 57 ◦ 05’ to 57 ◦ 07’ W, 124–128 m; fragment of a colony.

Paratypes. Same data as holotype; fragmentary colonies.

Description

Colony a brittle, unilaminar sheet, only loosely encrusted on substrata (fragments of erect bryozoans) such that basal surface of much of it is not attached. Autozooids elongate oval, convex, separated by distinct grooves. Frontal shield umbonulomorph, finely calcified, with a striated surface, rising distally and produced as a tall slen- der, cylindrical peristome, projecting almost perpendicularly from the frontal plane. Proximal half of frontal shield, and lateral and distal margins, closely pierced by small round pores; central region of frontal shield, and peristome, imperforate, ring scar on inner surface of frontal shield coinciding with curved border between perforate and imperforate areas. Peristome transversely oval at base, tapering distally to a more or less cylindrical cross-section, its proximal rim produced as a rounded lip; distal face of peristome shows a longitudinal suture, indicating where two lobes of developing peristome fuse. Ovicell hemispherical, imperforate, with a nodular surface; situated at base of peristome and opening into it; its orifice overhung by a projecting lip, which is obscured by the development of the peristome. Vertical walls of autozooids pierced by numerous small, uniporous septula. Basal wall with a drop-shaped lacuna, covered by dark brown cuticle, at extreme distal end. A broad lyrula projects from proximal face at base of peristome, occupying most of proximal rim; more or less anvil shaped, straight edged, with the distal corners distinctly bifid.

Measurements

Both measurements are for n = 20, mean ± SD: autozooid length 1.27 ± 0.12 mm; autozooid width 0.71 ± 0.08 mm.

Etymology

Greek, peri: around; stoma: mouth, alluding to the distinctive peristome.

Remarks

Lageneschara was introduced by Hayward and Thorpe (1988c) for the endemic Antarctic species,? Phylactella (sic) lyrulata Calvet, 1909 , which seems to be common, and widely distributed, in Antarctic shelf seas. Lageneschara lyrulata develops large, meandriform colonies formed of folded, brittle, unilaminar sheets. The autozooids are also large, to 2.0 mm long, with a broadly flask-like shape (lageniform) and the frontal shield, as in L. peristomata , displays a sharp boundary between a proximal perforate portion and a distal imperforate portion, with a distinct curving line of pores marking the position of the umbonuloid ring scar. Both species have a drop-shaped lacuna distally in the basal wall. The new species clearly belongs in Lageneschara , but is distinguished by its long cylindrical peristome, which is short and flared in the type species, and by its characteristic ovicell, with the projecting apertural lip. Description of this new species extends the distribution of the genus northwards of the Antarctic Circle.

Figures

Figure 15. Arachnopusia discors, Hero 69 (SOSC 10). (A) Ovicelled zooids; (B) detail to show subapertural plate; (C) large vicarious avicularia at the colony margin. Scale bars: 0.5 mm (A), 0.05 mm (B), 0.25 mm (C).

Figure 16. Lageneschara peristomata sp. nov., Paratype. (A) Group of ovicelled zooids; (B) zooid with broken peristome, showing lyrula; (C) detail to show developing peristome. Scale bars: 1.0 mm (A), 0.1 mm (B, C).