Schizoporella unicornis ( Johnston, 1847 )

Tompsett, Scott, Porter, Joanne S. & Taylor, Paul D., 2009, Taxonomy of the fouling cheilostome bryozoans Schizoporella unicornis (Johnston) and Schizoporella errata (Waters), Journal of Natural History 43 (35 - 36), pp. 2227-2243 : 2230-2233

Schizoporella unicornis ( Johnston, 1847)

( Figures 1E,F ; 2A–F )

? Lepralia coccinea (Abildgaard, 1806) : Johnston, 1838, p. 278, pl. 34, figs 1–3.

Lepralia unicornis Johnston, 1847, p. 321 , pl. 57, fig. 1.

Lepralia spinifera (var.) Busk, 1854, p. 69, pl. 81, figs 6–7.

Schizoporella unicornis (Johnston) : Hincks, 1880, p. 288, pl. 35, figs 1, 2, 4, 5; Lagaaij, 1952, p. 65, pl. 5, fig. 7; Ryland, 1965, p. 65, fig. 32a,b; Hayward and Ryland, 1999, p. 221, fig. 91a,b,c.

Schizoporella unicornis (Johnston, in Wood, 1844): Soule et al., 1995, p. 204, pl. 75, figures A–F.

Material

Lectotype. Designated by Lagaaij (1952), NHM 1847.16.174, Britain, Johnston Collection, figured by Johnston (1847, pl. 57, fig. 1) and Figure 2 (A,B) herein, an unbleached, unilaminar encrusting colony on the surface of a broken stone. NHM 1847.16.174(a) is a fragment of the lectotype bleached for SEM analysis ( Figures 1E,F , 2C–F herein).

Description

Colony encrusting, multiserial, unilamellar or multilamellar, generally less than 5 cm in diameter. Colour normally pink or whitish pink.

Autozooids large but variable in size, length 387–715 µm (mean 529 µm, SD 84.38 µm, n = 35), width 273–537 µm (mean 383 µm, SD 59.14 µm, n = 35), on average about 1.4 × longer than wide, broadening before row bifurcations, generally rectangular in shape with wide, squared distal end accommodating single or paired adventitious avicularia. Frontal shield convex, covered with numerous irregularly arranged pseudopores and deep marginal areolar pores. Umbo stout, congruent with boundary between pseudoporous and non-pseudoporous frontal shield. Pseudopores have small openings not changing in size or shape during secondary calcification. Primary orifice broader than long, length (including sinus) 115–145 µm (mean 131 µm, SD 8.32 µm, n = 25), width 143–186 µm (mean 163.5 µm, SD 10 µm, n = 25), anter forming a wide D-shape, sinus (poster) a broad U-shape. When the operculum is removed, orifice edge adjacent to condyles runs proximally from sinus to proximolateral corners (i.e. slopes downwards). Condyles prominent, fully visible above proximal edge of primary orifice, tips rounded and directed distally; viewed from within, condyles are clearly constructed from calcified oral rim.

Adventitious avicularia either single or paired, directed distolaterally from centre-line. Occasional additional adventitious avicularia developed on frontal shield proximal to primary orifice. In early ontogeny avicularia appear raised but are subsumed into frontal shield during secondary calcification. Rostrum acute with concave sides and upturned tip. Opesia rounded, D-shaped; crossbar without columella. Mandible with an acutely pointed distal tip curved upwards, Rostrum length 102–181 µm (mean 131 µm, SD 17 µm, n = 26), width of crossbar 56–83 µm (mean 68 µm, SD 7.5 µm, n = 26).

Ovicells found in localized clusters or more widely distributed, prominent, round and globular, recumbent on frontal shield of distal zooid, large, 247–356 µm (mean 292 µm, SD 29 µm, n = 26) long by 318–452 µm (mean 372 µm, SD 32 µm, n = 26) wide. Ooecial surface cryptocystal, bearing radially aligned, scalloped grooves around edges; pores few in number, present only at the periphery, centre imperforate.

Remarks

The type species of Schizoporella is commonly cited in taxonomic works as L. unicornis Johnston in Wood (1844). Wood’s paper described fossil bryozoans from the Pliocene Coralline Crag Formation of Suffolk, UK. However, the type material of S. unicornis is generally regarded as Recent (e.g. Lagaaij 1952; Soule et al. 1995), an anomaly pointed out by Berning (2006). The description by Wood (1844: 278) of the species, from the Coralline Crag locality of Sutton, is brief and lacks a figure:

“The aperture of this has vestiges of spines. The ovarian capsule above the aperture, observable in many specimens of this genus, will occasionally alter the shape of the aperture, and is itself sometimes worn into an opening.”

Tellingly, the species name is cited as “ Lepralia unicornis? Johnston MS. ”, suggesting that (1) Wood was uncertain of the identity of his material, and (2) he based his tentative determination on Johnston’s manuscript for the second edition of A History of the British Zoophytes ( Johnston 1847). The fact that a Recent specimen of L. unicornis was described comprehensively in Johnston’s later work, and is well figured, supports the interpretation of L. unicornis based on Recent rather than fossil material. Indeed, Lagaaij (1952) concluded that “The lectotype must be chosen from the specimens upon which Johnston originally based his identification” (p. 66), and went on to select a Recent specimen (NHM 1847.9.16.174) as lectotype. However, Lagaaij still placed L. unicornis (Wood ex Johnston, 1844) in synonymy with the Recent L. unicornis sensu Johnston. This synonymy is doubtful based on an SEM study of Wood’s Coralline Crag material ( Figure 1A–D ). Wood’s specimen, although poorly preserved, has a distinctly narrower and deeper sinus than the Recent lectotype of S. unicornis .

The Wood specimen figured herein ( Figure 1A–D ) shares many characters with Recent S. patula , including a deep V-shaped primary orifice, paired distolaterally directed avicularia and umbo. However, Bishop and Hayward (1989) stated that many species of Schizoporella from the British, Dutch and Belgian Pliocene should be considered as S. dunkeri , which they figure from the Pliocene of Belgium (their fig. 67-9) with a columella. A columella is not visible on the Wood specimen but this may reflect its poor state of preservation. The only recent European species described to have a columella is S. cornualis ( Hayward and Ryland 1995) .

Schizoporella unicornis appears to have a geographical range in the northeast Atlantic, from northwest Africa and Spain to the Faeroes and Western Norway ( Hayward and Ryland 1999). It is found commonly encrusting the undersides of stones, shells and kelp holdfasts at or slightly below low water spring tide.

The ancestrula is not visible in the lectotype of S. unicornis . However, according to Ryland (1965) and Hayward and Ryland (1999), this is tatiform in S. unicornis , with eight oral spines.

Figures

Figure 1. (A–D) Images of Wood’s Pliocene specimen from the Coralline Crag, Suffolk (NHM B1675) described in Busk (1859). (A) Group of autozooids at growing edge of colony within small bivalve shell. (B) Autozooids exhibiting deep V-shaped sinus. (C) Frontal shield with paired avicularia and deep V-shaped sinus. (D) Detail of primary orifice and sinus. (E, F) Lectotype of Schizoporella unicornis [NHM 1847.16.174 (a)] bleached portion. (E) Group of autozooids at the distal edge of colony with adventitious avicularia, paired, single or absent. (F) Ovicellate autozooids showing radially aligned scalloped grooves. Scale bars: 500 µm (A); 250 µm (B); 100 µm (C, E); 50 µm (D,F).

Figure 2. (A, B) Lectotype of Schizoporella unicornis (NHM 1847.16.174) unbleached portion. (A) Group of ovicellate autozooids. (B) Primary orifice with operculum and paired adventitious avicularia. (C–F) Lectotype of Schizoporella unicornis [NHM 1847.16.174 (a)] bleached portion. (C) Autozooids with detail of ovicell structure. (D) Detail of primary orifice and adventitious avicularium. Note the wide U-shaped sinus and prominent condyles. (E) View of primary orifice from the interior of the autozooid, showing condyles formed from frontal shield calcification. (F) Autozooid with additional adventitious avicularium. Scale bars: 250 µm (A, C, F); 100 µm (B); 50 µm (D, E).