Osthimosia minuscula, 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 : 2325-2326

Family CELLEPORIDAE Johnston, 1838

Osthimosia minuscula sp. nov.

( Figure 31A, B )

Material

Holotype. NMNH 1154044 : Eltanin cruise 5, station 219, 55 ◦ 47’ to 55 ◦ 52’ S, 66 ◦ 17’ to 66 ◦ 24’ W, 115 m, 23 September 1962; a pisiform colony 0.21 mm diameter, encrusting a fragment of Spigaleos striatula .

Paratypes. NMNH 1154044 : same data as holotype; three similar colonies, 0.13, 0.11, 0.07 mm diameter, and a cylinder 0.37 mm long; substrata unknown .

Description

Colony small, pisiform or cylindrical, with autozooids tightly but irregularly packed, with peristomes projecting substantially above colony surface. Primary orifice with transversely elliptical anter, defined by comparatively large, rounded and faceted condyles; poster irregularly concave, with the rounded base of the peristomial avicularium protruding medially. Peristome deep, completely obscuring primary orifice, its rim flared and bearing a small avicularium medio-proximally, the rostrum 0.04 mm long, directed proximally, elongate oval, lacking palate, the slender crossbar without a columella; the avicularian cystid forms a prominent ridge running down the inner face of the peristome. Ovicell hyperstomial, spherical, 0.16 mm diameter, its aperture with a distinct distal lip, opening into the peristome; frontal surface of ectooecium almost entirely membranous, the smoothly calcified entooecium with small marginal foramina proximo-laterally; the peristome is enclosed on each side by a lobe of the peristome, the two lobes developing narrow extensions on to the frontal surface of the ovicell. Interstices between autozooids are infilled by irregular, variously sized vicarious avicularia, the tumid cystids each with two to four (more?) large, marginal pores, and centrally a small oval rostrum, with slender crossbar but no palate, supporting a small semi-elliptical mandible.

Etymology

Latin, minuscula , from minus: less, with reference to the minute size of the colony.

Remarks

Osthimosia minuscula is similar to the Antarctic species O. mariae Hayward, 1992 , which is also characterized by its tiny colonies, and in which the primary orifice is hidden by a tall, flaring peristome. It is distinguished from that species by the shape of the primary orifice, which is orbicular in O. mariae , with a broadly U-shaped sinus between inconspicuous condyles, and by the unusual vicarious avicularia.

Figures

Figure 31. (A,B) Osthimosia minuscula sp. nov., Paratype. (A) Portion of colony showing morphology of peristome and ovicell; (B) detail to show primary orifice. (C–E) Osthimosia multifaria sp. nov., Holotype. (C) Portion of colony with columnar peristomial avicularia, ovicell and large vicarious avicularium; (D) detail showing primary orifice, ovicell and peristomial avicularia; (E) smaller vicarious avicularium, with asymmetric rostrum. Scale bars: 0.15 mm (A), 0.025 mm (B), 0.25 mm (C), 0.2 mm (D), 0.1 mm (E).