Sarsiflustra japonica Silén, 1938

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 : 40-42

Sarsiflustra japonica Silén, 1938

( Fig. 19 ; Table 18)

Sarsiflustra japonica Silén, 1938: 351 , text-figs 72–75, pl. 18, fig. 122.

Material examined. Lectotype (designated here) UPSZTY 2476 B ( Fig. 19A–C ), Okinose , Sagami, Japan; depth 150–600 m. Leg. Prof. S. Bock 1914 . Paralectotype UPSZTY 2476 A ( Fig. 19D ), same details as the lectotype .

Description. Colony erect, developing multiserial, bilamellar, flat, fan-shaped fronds, starting from a stalked ancestrula attached to the substrate by a small, circular basal portion ( Fig. 19A ).

Ancestrula erect, proximal part of cystid columnar, broadening to an elongate-oval dilatation bearing the opesia, 910–980 × 540–550 µm, the column 1 mm long, with regular constrictions and horizontal growth lines, tapering towards the encrusting base from c. 350 µm to 250 µm, the encrusting base c. 530 µm in maximum diameter; ancestrula budding three autozooids, one distal and two distolateral; the distally budded zooid smaller, 580–820 × 420–475 µm, rounded rectangular, the two distolaterally budded zooids larger, 650–995 × 530–620 µm, and irregularly shaped, the whole frontal surface occupied by the frontal membrane ( Fig. 19A ).

Autozooids rounded hexagonal or pentagonal, almost twice as long as wide (mean L/ W 1.89), distinct, separated by shallow grooves and a slightly raised distal margin, arranged in radial rows and back to back; frontal surface entirely occupied by the frontal membrane, gymnocyst absent, cryptocyst minimal, visible distolaterally, faintly granular ( Fig. 19B ).

Avicularia vicarious, as large as autozooids, placed at row bifurcations, budded distolaterally, tongue-shaped with pointed proximal margin, and with slightly more than half of the frontal surface occupied by the rounded triangular to spatulate mandible ( Fig. 19B ), 320–500 µm long; rostrum with a distal, depressed cryptocystal shelf 180 µm wide, opening semielliptical to semicircular, c. 215 × 260 µm ( Fig. 19C ).

Kenozooids developed at the lateral margins of the colony fronds, irregularly triangular, 520–750 × 275–360 µm ( Fig. 19D ).

Ovicells absent.

Remarks. Silén (1941) stressed the importance of avicularia to distinguish between very similar genera of Flustridae . Sarsiflustra is defined as the flustrid genus in which vicarious avicularia are budded distolaterally from the mother zooid and placed at the bifurcation of zooidal rows, are the same size as autozooids, have pointed proximal margins and half of the frontal surface occupied by a lingulate (i.e. tongue-shaped) mandible. The molecular phylogeny of Orr et al. (2022), which includes species of some flustrid genera (i.e. Chartella , Flustra , Hincksina , Klugeflustra , Nematoflustra , Retiflustra , Securiflustra , Sinoflustra ), shows that the family Flustridae , as currently defined, is polyphyletic with only Hincksina , Chartella , Securiflustra and Flustra forming a wellsupported, monophyletic clade, confirming previous hypotheses regarding the heterogeneity of this family (e.g. Silén 1941; Martha et al. 2020).

The only other species of the genus Sarsiflustra , S. abyssicola ( Sars, 1872) , differs from S. japonica in having the colony starting with a broad encrusting sheet of autozooids ( Hayward & Ryland 1998), instead of an erect ancestrula with a small encrusting base, and in the presence of immersed ooecia with an apical pore, while the present species is considered to brood embryos fully internally ( Silén 1938).

Figures

FIGURE 19. Sarsiflustra japonica Silén, 1938, Japan. A–C. Lectotype UPSZTY 2476B. A. Ancestrula and early astogeny. B. Close-up of autozooids and vicarious avicularia. C. Close-up of an avicularium lacking the mandible and showing the semicircular opening and the cryptocystal shelf of the rostrum. D. Paralectotype UPSZTY 2476A, irregularly shaped kenozooids at the lateral margins of the colony frond. Scale bars: A, B, D = 500 µm; C = 200 µm.