Arachnopusia incernicula, Hayward & Winston, 2011

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 : 2290

Arachnopusia incernicula sp. nov.

( Figure 14C, D )

Material

Holotype. NMNH 1154029 : Eltanin cruise 9, station 740: 56 ◦ 06’ to 56 ◦ 07’ S, 66 ◦ 19’ to 66 ◦ 30’ W, 494– 384 m, 18 September 1963; two fragments of a single colony, detached from substratum (possibly a sponge).

Paratypes. VMNH 013669.00: same data as holotype; five fragments .

Description

Holotype colony encrusting, unilaminar. Autozooids oval to quadrangular, gently convex, separated by distinct sutures, commonly 0.87 × 0.62 mm. Frontal shield with c.40 small, closely spaced foramina, each deeply recessed and with a thick ligula obscuring half of the lumen, the whole resembles a fine sieve with small reniform pores. Aperture wider than long, the distal edge hidden in frontal view by a projecting proximal lip incorporating two small avicularia. Apertural plate ( Figure 14D ) wider than long, smooth surfaced; proximal edge thin and convex, the distal edge forming a thickened rim. A pair of short, thin spines present on the distal edge of the aperture in earliest ontogeny, but soon obscured; a single, stout lateral oral spine on one side of aperture, and a small lateral oral avicularium present on its opposite rim. Avicularia sparsely developed, generally small; lateral oral avicularium c. 0.07 mm long, with short rostrum proximally directed, tilted towards aperture; a larger avicularium typically present close to the lateral oral spine, just frontal to the peristome rim, rostrum 0.175 mm long, slightly acute to frontal plane, directed proximo-laterally. Additional avicularia, similar in shape and size to the lateral oral avicularium, may be present distal to the aperture, with rostra directed towards aperture, and two or more may be present on the proximal peristomial lip, with rostra directed frontally; in all avicularia the rostrum is upturned and pointed distally, supporting a slender triangular mandible, there are two small condylar knobs, and the palate is lacking. Ovicell about as wide as long, with a broad band of exposed entooecium bordering its aperture, bounded distally by a conspicuous ridge; immersed in a thickening ooecial cover in later ontogeny.

Etymology

Latin, incernicula : a sieve, with reference to the finely porous frontal shield.

Remarks

Arachnopusia incernicula sp. nov. is most similar to A. tubula Hayward and Thorpe, 1988 , described from Elephant Island, South Shetland Isles, in its large, almost flat, apertural plate, and its projecting peristomial lip. However, in that species the frontal shield is perforated by fewer (20–30), larger foramina, and the peristomial lip bears a fan of three small avicularia. The lateral oral avicularium may be single or paired in A. tubula , with the rostra of both tilted towards the aperture, but the larger avicularium associated with the lateral spine, a consistent character of A. incernicula , is absent in A. tubula . Finally, the exposed area of entooecium is more extensive in A. tubula than in A. incernicula , broadly triangular in shape and with a coarsely granular surface.

Figures

Figure 14. (A,B) Arachnopusia pelvicula sp. nov., Holotype. (A) Ovicelled zooids, centre and top left, with frontal shields of adjacent zooids, right and top; (B) detail to show subapertural plate. (C,D) Arachnopusia incernicula sp. nov., Paratype. (C) Group of ovicelled zooids; (D) detail to show subapertural plate in two zooids. Scale bars: 0.5 mm (A, D), 0.25 mm (C), 0.05 (B).