Stephanotheca ipsum, Cumming, Robyn L., 2015

Cumming, Robyn L., 2015, Two tropical species of Stephanotheca (Bryozoa, Cheilostomata, Lanceoporidae) from the Gulf of Carpentaria, Australia, Zootaxa 3948 (2), pp. 279-286 : 280-283

Stephanotheca ipsum n. sp.

( Figure 1 , Table 1 )

Material Examined. Holotype: MTQ G26766, southeastern GoC, 16°40.914’ S, 140°12.092’ E, encrusting Cigclisula sp., 33 m. Paratypes: MTQ G26767, encrusting Cigclisula , same data as for holotype; MTQ G26768, eastern GoC, seabed surrounding submerged coral reef, 15°15.561’ S, 140°22.905’ E, encrusting Steginoporella sp., 49 m.

Etymology. From the Latin ipsum for button, for the button-like roundness of the primary orifice, the sinus and the adventitious avicularia.

Description. Colony encrusting; autozooids irregularly hexagonal (c. 0.4 x 0.3 mm; Table 1 ); frontal shield flattened to slightly convex; pseudopores relatively small (c. 0.008 mm diameter) and widely spaced, separated by more than two pseudopore diameters (c. 43 per zooid), rounded to elongate, extending to zooid margins; interzooidal boundaries marked by thin grooves and occasional elongate sutural pores; walls between zooids with 3–4 uniporous septula.

Primary orifice as wide as long (c. 0.10 x 0.10 mm); anter round; lunula restricted to distal half of orifice; sinus a wide rounded arc; condyles large, elongate, serrate.

Each zooid with a single, small, round, suboral, medial adventitious avicularium (c. 0.04 mm diameter), cystid raised proximally, directed proximofrontally; proximal opesia and rostral foramen oval; mandible semicircular; crossbar complete; sometimes one, rarely two, additional avicularia of same shape and size proximally, adjacent to orifice of an adjacent zooid, directed distolaterally; vicarious avicularia not observed.

Ooecium wider than long (c. 0.3 x 0.2 mm), immersed, bordered by ridge of calcification that is sometimes complete, sometimes restricted to distal edge, not crossed by suture lines; orifice dimorphic, the ovicellate orifice significantly wider than autozooidal orifice (c. 0.12 vs 0.10 mm; 1-tailed t-test: p<0.001; Table 1 ).

Remarks. Stephanotheca ipsum n. sp. is distinguished by its rounded orifice with semicircular sinus, small, round avicularia suborally and proximally, and the extensively pseudoporous ooecium with a low ridge of peripheral calcification. It shares with other Stephanotheca species an encrusting growth form and a proximally directed, medial adventitious avicularium. No other Stephanotheca species have more than one adventitious avicularium per zooid, except S. romajoyae n. sp.

Stephanotheca ipsum n. sp. is provisionally placed in Stephanotheca on the basis of the ridged ooecium, which differs from the fully pseudoporous ooecium of Calyptotheca and resembles the crowned ooecium of Stephanotheca in having a porous area surrounded by an imperforate area. On the one hand, it resembles S. perforata Reverter-Gil, Souto & Fernández-Pulpeiro, 2012 , from the Mediterranean, which also has a ridged ooecium instead of the crowned ooecium typical of European Stephanotheca , but only one ooecium was present in the material and the morphological variability is unknown ( Reverter-Gil et al. 2012). On the other hand, it resembles C. inclusa ( Thornely, 1906) , an Indo-Pacific species, which has a single, near-circular, suboral medial avicularium on each zooid and ooecia with a ridge [called a “calcareous arch” by Thornely (1905, p. 116, plate, fig. 2, as Schizoporella avicularis )]. However, Harmer (1957, p. 1029, pl. 66, fig. 4) noted C. inclusa specimens were only “sometimes bordered by a smooth, semicircular ridge”. This feature has not appeared in subsequent descriptions and illustrations of C. inclusa by Ristedt & Hillmer (1985), Winston & Heimberg (1986), Hayward (1988), Scholz (1991), Ryland & Hayward (1992) and Tilbrook (2006). Stephanotheca perforata differs from C. ipsum n. sp. in having a much larger orifice (0.15 x 0.15 mm vs 0.10 x 0.10 mm), more numerous and more closely spaced pseudopores in the frontal shield (approx. 75 vs mean 43), and only a single, oval avicularium, often wanting, whereas S. ipsum has up to three round avicularia on each zooid, one suborally and one or two proximally. Calyptotheca inclusa differs from S. ipsum n. sp. by its pear-shaped orifice with deeper, narrower sinus, larger, more oval suboral avicularia with trifoliate distal opesia, no proximal adventitious avicularia, and occasional vicarious avicularia.

Calyptotheca inclusa belongs to a group of similar species with a single, oval or round, suboral, medial avicularium on each zooid. Of these, C. immersa ( Powell, 1967) , C. lardil Cumming & Tilbrook, 2014 , C. reniformis Tilbrook, 2006 and C. rugosa Hayward, 1974 (p. 379, fig. 5a) have the fully perforated ooecia of Calyptotheca , but ooecial details are not known for C. kapaaensis Dick, Tilbrook & Mawatari, 2006 , C. subimmersa (MacGillivray, 1879) , Schizomavella collina Cook, 1965 and S. incompta Hayward, 1988 (p. 315, pl. 7e), in most cases because ooecia were not present in the material. It remains possible that some of these latter species have ridged ooecia. Only one of these, S. incompta , has additional proximal avicularia, but unlike those of C. ipsum n. sp., they are dimorphic, the proximal avicularia being triangular and larger.

The ooecia of the two southern Australian Stephanotheca species, S. ambita Reverter-Gil, Souto & Fernández- Pulpeiro, 2012 and S. victoriensis Reverter-Gil, Souto & Fernández-Pulpeiro, 2012 , also vary from the typical crowned ooecium of the European species. Those of S. ambita have a relatively larger perforated area and smaller, lower nodular rim of calcification, which is nevertheless larger than the ridge of S. ipsum n. sp. and S. perforata . Those of S. victoriensis are neither crowned nor ridged, but instead have a wide arch of pseudopores, and a few pseudopores scattered frontally. Stephanotheca victoriensis is only provisionally placed in the genus ( Reverter-Gil et al. 2012). Stephanotheca ambita shares with S. ipsum n. sp. a relatively small round orifice with wide, shallow sinus, and small, suboral, proximofrontally directed avicularia, but differs in having non-serrate condyles, oval rather than round avicularia, only one avicularium per zooid, and different ooecial morphology. Stephanotheca victoriensis has a wider, distinctly oval orifice, a single, oval, much larger avicularium distant from the orifice and almost in the centre of the zooid, and different ooecial morphology.

Distribution. Stephanotheca ipsum n. sp. is known only from the GoC. Two colonies are from the same site east of Mornington Island in the southeastern GoC, encrusting the foliaceous habitat-providing bryozoan Cigclisula sp. at 33 m. The third colony is from the seabed surrounding a submerged coral reef in the eastern GoC, encrusting the platelike habitat-providing bryozoan Steginoporella sp. at 49 m.

Figures

FIGURE 1. Stephanotheca ipsum n. sp. A, B, D, F, paratype (MTQ G 26768), C, E, holotype (MTQ G 26766): A, whole colony; B, primary orifice with suboral avicularium; C, autozooid and ovicellate zooid; note the ridged ooecium; D, marginal autozooids; note septula in lateral walls; E, ooecium; F, primary orifice with operculum.

Tables

TABLE 1. Measurements (mm) and counts for Stephanotheca ipsum n. sp. Zooid, orifice, avicularia and ovicell measurements on holotype (MTQ G 26766), pseudopore measurements on MTQ G 26768.

	Mean	Standard deviation Range	N
Zooid length	0.446	0.060 0.369–0.558	10
Zooid width	0.256	0.063 0.190–0.353	10
Autozooid orifice length	0.096	0.004 0.090–0.101	10
Autozooid orifice width	0.100	0.003 0.094–0.104	10
Adventitious avicularium length	0.040	0.003 0.035–0.045	10
Adventitious avicularium width	0.039	0.001 0.038–0.042	10
Diameter of pseudopores in frontal shield	0.008	0.001 0.007–0.010	10
Number of pseudopores in frontal shield	43.4	4.648 36–49	10
Ooecium length	0.218	0.027 0.188–0.247	5
Ooecium width	0.274	0.062 0.211–0.376	5
Ovicellate orifice length	0.087	0.003 0.085–0.090	3
Ovicellate orifice width	0.117	0.007 0.113–0.126	3