Mangana incrustata ( Silén, 1941 ) Martino, 2023

Martino, Emanuela Di, 2023, Scanning electron microscopy study of Lars Silén’s cheilostome bryozoan type specimens in the historical collections of natural history museums in Sweden, Zootaxa 5379 (1), pp. 1-106 : 31-33

Mangana incrustata ( Silén, 1941) n. comb.

( Fig. 14 ; Table 14)

Tegella incrustata Silén, 1941: 29 , figs 27–30, pl. 2, fig. 5.

Material examined. Holotype by original designation UPSZTY 2474 ( Fig. 14A, B ), Goto Islands , Kyushu, Japan; depth 110 m; encrusting a sponge from a sandy sea-bottom. Leg. Prof. S. Bock 1914 . Paratype UPSZTY 191149 ( Fig. 14C, D ), Bonin Islands (Ogasawara), Japan; depth 100–135 m; encrusting a fragment of a sea-urchin test. Leg. Prof. S. Bock 1914 .

Description. Colony encrusting, multiserial, unilaminar ( Fig. 14C, D ). Ancestrula tatiform ( Fig. 14D , see dashed ellipse), elliptical, c. 165 × 95 µm, surrounded by at least six spines (20–25 µm in diameter), budding a single autozooid distally; the first budded autozooid oval, c. 430 × 225 µm, seemingly equipped with a proximal avicularium as later autozooids; subsequent autozooids budding in a spiral pattern, constraining and overgrowing the ancestrula.

Autozooids oval to club-shaped depending on the extension of the proximal gymnocyst ( Fig. 14C ), longer than wide (mean L/ W 1.44), distinct, separated by thin grooves, irregularly arranged. Vestigial traces of gymnocyst visible proximal to the depressed rectangular to trapezoidal platform lodging the avicularium ( Fig. 14C, D ), 75–210 µm long, finely granular; opesial cryptocyst outlined by a raised beaded rim, narrow (30–45 µm), evenly extended proximally and laterally, disappearing distally, coarsely granular with granules 5–12 µm in diameter aligned in radial row and projecting inwards, giving the opesia a denticulate appearance ( Fig. 14D ).

Autozooidal appearance changing through the development of a calcified ‘lamina’ (i.e. interior walled cryptocystal layer of kenozooidal origin; Fig. 14A, B ): zooidal boundaries becoming indistinct while undulate sutures appear at about zooidal mid-length, at level with the base of the avicularium, joining the two portions of lamina covering each autozooid, one that starts spreading proximally and the other distally. Surface of the lamina flat, granular, with granules evenly distributed and widely spaced on the frontal, more densely accumulated on the avicularian mucro and ovicells, 8–15 µm in diameter; 2–6 elliptical to subcircular pores distributed more or less along the obliterated lateral boundaries of the zooids, 20–70 × 15–50 µm.

Opesia oval, occupying most of the frontal surface (mean OpL/ZL 0.74), rarely with 1–2 distolateral spines c. 30 µm in diameter (see arrows in Fig. 14A, C ); if present, spines persisting in ovicellate autozooids concealed by the calcified ‘lamina’ ( Fig. 14A ). Opesia partly obscured by the development of the lamina leaving a bell- to figure-eight-shaped secondary opening, 350–450 × 180–220 µm; the proximal margin always hidden by the rising avicularium, the distal margin straight and truncated if an ovicell develops ( Fig. 14A, B ).

A large frontal avicularium (215 µm long by 130 µm wide) obliquely placed on the proximal zooidal gymnocyst of each autozooid, forming a prominent mucro projecting over the opesia (185–210 µm in length from the proximal margin of the secondary opening) at an angle of about 10–20° when covered by the calcified ‘lamina’, therefore not visible in frontal view ( Fig. 14A, B ); the outline of the rostrum smooth, the surface of ‘lamina’ covering the avicularian chamber densely granular; rostrum triangular, hooked, laterally serrated pointing distally or distolaterally; crossbar seemingly complete.

Ovicells globular, convex, semi-immersed in proximal part of distal zooid; ooecium covered by the calcified ‘lamina’, densely granular ( Fig. 14A ), with the subcircular/elliptical pores of the ‘lamina’ distributed at each corner, the proximal margin straight.

Remarks. As for Mangana canui n. comb., the newly proposed combination, M. incrustata n. comb., is also based on the presence of the same key foveolariid characters, i.e. negligible gymnocyst and interior walled cryptocystal layer of kenozooidal origin. Once again, the presence of a large frontal adventitious avicularium proximally to each autozooid classifies this species within the genus Mangana . Furthermore, it is worth noting that oral spines in this species may either be present or absent in autozooids within the same colony.

Silén (1941, p. 31) compares this species with Tegella robertsoni O’Donoghue & O’Donoghue, 1926 [now considered a junior synonym of T. aquilirostris ( O’Donoghue & O’Donoghue, 1923) ] because of a similar secondary calcified ‘lamina’ that, however, is unrelated to the thin kenozooidal overgrowth layer in M. incrustata n. comb. In T. robertsoni , the secondary ‘lamina’ to which Silén (1941) referred would cover only the ooecium “which is small and membranous or very little calcified”. It is likely that Silén (1941) referred to the thick margin of the ectooecium (see Dick et al. 2005, p. 3708, fig. 4E, F).

Among species currently assigned to Tegella , T. horrida ( Hincks, 1880) shares similarities with M. canui n. comb., M. incrustata n. comb., and foveolariids in general. Notably, T. horrida has interior-walled excavations on the ovicell and interzooidal kenozooids ( Dick et al. 2005). The presence of a large proximofrontal avicularium in T. horrida strongly suggests its affinity with M. canui n. comb. and M. incrustata n. comb. In addition, all three species are geographically close, being found in the North Pacific. The main difference lies in the robust and prominent circumopesial spines present in T. horrida .

Mawatari (1952) reported this species also from one locality (i.e. Kushimoto) at Kii Peninsula.

Figures

FIGURE 14. Mangana incrustata (Silén, 1941) n. comb. A, B. Holotype UPSZTY 2474, Goto Islands, Japan. A. Group of zooids, two ovicellate. Arrows indicate distolateral opesial spine bases. B. Close-up of two autozooids and an avicularium. C, D. Paratype UPSZTY 191149, Bonin Islands, Japan. C. Group of zooids showing the variable appearance owing to the development or not of the calcified ‘lamina’.Arrows indicate distolateral opesial spine bases. D. Ancestrula (see dashed ellipse) and first budded autozooids lacking the calcareous lamina. All scale bars are 200 µm.