Oncousoecia lobulata Canu, 1918

Taylor, Paul D. & Zatoń, Michał, 2008, Taxonomy of the bryozoan genera Oncousoecia, Microeciella and Eurystrotos (Cyclostomata: Oncousoeciidae), Journal of Natural History 42 (39 - 40), pp. 2557-2574 : 2562-2563

Oncousoecia lobulata Canu, 1918

( Figures 1C ; 2A–D )

non Tubulipora lobulata Hassall 1841, p. 367 , Plate 10, Figures 1 , 2 [5 Tubulipora sp. ]. Tubulipora lobulata Hassall : Hincks 1880, p. 444 (part), Plate 50, Figure 5, 5a only; Bassler 1953, Figure 18.1.

Tubulipora lobulata Hincks : Canu 1918, p. 325.

Oncousoecia (Tubulipora) lobulata Hincks : Canu and Bassler 1920, Figure 226A, B. Oncousoecia dilatans (Johnston) : Hastings 1963, p. 117 (part), Plate 3, Figure 2 , Text- Figure 2 only.

Material

Lectotype (here chosen). NHM 1911.10.1.86, Shetland, Norman Collection, figured by Hincks (1880, Plate 61, Figure 5, 5a ) whose figure was redrawn by Canu and Bassler (1920, Figure 226A, B) and Bassler (1953, Figure 18.1), the specimen being refigured by Hastings (1963, Plate 3, Figure 2 , text-Figure 2) ( Figures 1C ; 2A–D herein). This colony, encrusting the exterior of a small bivalve shell, is unbleached and was not cleaned before scanning electron microscopy, hence the blotches that are visible, especially in Figure 2 (B, D).

Description

Colony encrusting ( Figure 1C ), small (9 mm maximum diameter in lectotype), comprising bifurcating, lobate ( Figure 2A ), mildly convex, oligoserial branches with autozooids diverging slightly from branch axes and kenozooids developed along sloping lateral margins; branch width typically about 1 mm. Early zooids damaged in lectotype, ancestrula destroyed.

Autozooids elongate ( Figure 2B ), 0.58–0.75 mm long by 0.20–0.25 mm wide, frontal walls convex, more so distally; pseudopores sparse, spaced irregularly, aligned along furrows of calcification, teardrop-shaped, pointed distally, about 10 mm wide, lumen partly occluded by minute spines growing inwards from perimeter. Apertures subcircular, 0.08–0.11 mm in diameter, distributed more or less quincuncially, neither clustered nor connate; apertural rims thick but preserved peristomes short; terminal diaphragms not observed.

Gonozooids small with short, longitudinally ovoidal brood chamber ( Figure 2C ), 0.54–0.70 mm long by about 0.35 mm wide, slightly bulbous, edges indented by neighbouring autozooids but roof not pierced by peristomes; frontal wall densely pseudoporous, the pseudopores ( Figure 2D ) identical in shape to those of autozooids and similarly occluded partially by spines. Ooeciopore terminal, slightly transversely elliptical, smaller than an autozooidal aperture, about 0.06 mm in diameter; ooeciostome simple, short.

Remarks

Hastings (1963) was mistaken in placing this species in synonymy with Oncousoecia dilatans ( Johnston, 1847) , a view that led to some subsequent authors quoting O. dilatans (Johnston) as the type species of Oncousoecia . As described below, O. dilatans is a more delicate species than O. lobulata with appreciably smaller autozooids and pseudopores that are also significantly smaller, more regularly spaced and, moreover, lack the centripetal spines seen in O. lobulata (compare Figures 2D and 4G ). There are no major differences in gonozooid morphology between the two species, although brood chambers in the studied examples of gonozooids of O. dilatans do tend to have better-defined ovoidal outlines. Lateral branches are lacking in the lectotype of O. lobulata but occur occasionally in O. dilatans .

Figures

Figure 1. Photographs of type specimens of some Recent oncousoeciid cyclostome species. (A) Lectotype of Oncousoecia dilatans (Johnston, 1847) showing colony ramifying across the interior of a small bivalve shell (NHM 47.9.18.59). (B) Lectotype of Alecto compacta Norman, 1867, a subjective junior synonym of O. dilatans (NHM 11.10.1.63). (C) Lectotype of Oncousoecia lobulata Canu, 1918, the colony figured by Hincks (1880, Plate 50, Figure 5, 5a) as Tubulipora lobulata Hassall, 1841 which apparently formed the basis for Canu’s type species of Oncousoecia (NHM 1911.10.1.86). (D) Lectotype of Microeciella suborbicularis (Hincks, 1880), a subcircular colony with associated spirorbids (NHM 99.5.1.1427a). Scale bars: 5 mm (A, D); 1 mm (B, C).

Figure 2. Oncousoecia lobulata Canu, 1918, lectotype (NHM 1911.10.1.86). (A) Lobate, oligoserial branches; (B) autozooids; (C) gonozooid; (D) gonozooidal pseudopores showing partial occlusion by spines. Scale bars: 1 mm (A); 200mm (B, C); 50 mm (D).

Figure 4. Oncousoecia dilatans (Johnston, 1847). (A, C, D) Lectotype of Alecto compacta Norman, 1867 (NHM 11.10.1.63); (A) oligoserial branches close to colony origin; (C) gonozooid; (D) another gonozooid illustrating within-colony variability in shape. (B, G) Colony sharing the same substrate as the lectotype (NHM 11.10.1.63); (B) mass of branches overgrowing colony origin; (G) frontal wall of autozooids showing pseudopores and a larger boring. (E, F) Bleached topotype colony (NHM 11.10.1.64); (E) gonozooid; (F) two branches with intact and broken gonozooids. Scale bars: 1 mm (A); 500 mm (B, F); 200mm (C, D, E); 50 mm (G).

Figure 5. Comparison of early astogeny in (A–C) Alecto compacta (Norman, 1867) [5Oncousoecia dilatans (Johnston, 1847)] (NHM 11.10.1.64) and (D–F) Microeciella suborbicularis (Hincks, 1880), two species formerly considered synonymous. (A) Ancestrula and first budded zooids; (B) ancestrula with short distal tube; (C) large protoecium with tiny pseudopores around perimeter (best seen top right); (D) fan-shaped young colony; (E) ancestrula with long distal tube; (F) protoecium with a few, non-perimetrical pseudopores and two larger, enigmatic punctures or borings (left). Scale bars: 500 mm (D); 200mm (A); 100 mm (B, E); 50 mm (C, F).