Fedorella minima Silén, 1947

Martino, Emanuela Di, 2022, Revision of the type species of some cheilostome bryozoan genera in the collection of the Swedish Museum of Natural History, Zootaxa 5125 (2), pp. 157-181 : 168-171

Fedorella minima Silén, 1947

( Figs 6 , 7 ; Table 5)

Fedorella minima Silén, 1947: 55 , text-figs 46–48, pl. 4, fig. 24.

Material examined. Lectotype (designated here) SMNH-128088a ( Fig. 7A–C ), tropical Atlantic Ocean, Anguilla, 18˚N 62˚W, depth 182–455. Leg. A.v. Goës 1869 (1861 in Silén 1947) . Paralectotypes SMNH-128088b-h (seven colonies, two of which are figured here, Fig. 7D–F ), same details as the lectotype. Paralectotypes SMNH-Type-8734, tropical Atlantic Ocean , Anguilla, 18˚N 62˚W, depth 364–546 m, ooze; 13 colonies (three of which figured here, Fig. 6 ). Leg. A.v. Goës 1869 .

Description. Colony oval to pear-shaped ( Figs 6A, C , 7A ), 1.00– 1.74 mm long by 0.88–1.37 mm wide (L/ W 1.00 –1.76, N 15), likely to be supported above the substrate by rhizooids.

Autozooids arranged in 5–6 whorls of up to 10–12 zooids each (the highest number of zooids usually at colony mid-length), distinct with deep grooves and a thin rim of smooth calcification, irregularly polygonal, pentagonal, hexagonal or rectangular, with undulate margins, almost equidimensional (mean L/ W 1.01).

Frontal shield imperforate and coarsely tubercular; tuberculation seemingly increasing with ontogeny ( Fig. 7A ); tubercles in the first two generations of zooids concentrated along the proximal and lateral margins of the zooid leaving the centre completely smooth ( Figs 6D , 7E, F ); in some zooids two pairs of circular marginal areolar pores visible laterally, one pair proximally and the other pair distally, at about the same level as orifice mid-length ( Fig. 6D ).

Primary orifice cleithridiate, slightly longer than wide (mean L/ W 1.1), a horseshoe-shaped anter separated from a widely arcuate sinus by two small pointed triangular condyles proximomedially directed ( Figs 6B , 7B ). Paired oral spine bases present distolaterally only on the first two generations of autozooids ( Figs 6D arrowed, 7F). Smooth closure plates observed sealing the orifice of the zooids in the first whorls ( Fig. 7F )

Adventitious avicularia of two types, present on the majority of autozooids, single or paired, placed lateral to the orifice; type 1 avicularia drop-shaped, small, with slightly raised, triangular rostrum directed laterally ( Figs 6D , 7E, F ) or slightly distolaterally ( Figs 6B, D , 7B ), with complete crossbar, placed at level with the distal third of orifice length; type 2 avicularia spatulate, large, with raised, spoon-shaped, serrated rostrum ( Figs 6B , 7B, C ) directed distally or slightly distolaterally, with complete crossbar, placed at level with the orifice proximal margin. When paired, three combinations of avicularia types were observed: (i) two small drop-shaped ( Figs 6D , 7B ); (ii) one small drop-shaped and one large spatulate ( Fig. 6B ); (iii) two large spatulate ( Fig. 7B, C ). When single, either types of avicularia observed (e.g. only type 1 see Figs 6D , 7E, F ; only type 2 see Fig. 6C ).

Ovicells prominent, globular, occupying the entire length of the frontal shield of the next distal zooid; ooecium coarsely tubercular as zooidal frontal shield but evenly and densely pseudoporous; pseudopores circular, about 10 µm in diameter, placed at the centre of subcircular pits, about 25 µm in diameter ( Fig. 7C, D ); ooecial aperture large, about 85 x 105–125 µm, rounded triangular ( Fig. 7D ), not closed by the zooidal operculum.

Kenozooids rare, rectangular, as long as autozooids but narrower, without openings but with two marginal areolae at opposite corners as seen also in autozooids ( Fig. 6D asterisk), seemingly space-fillers owing to colony reparation.

Intramural budding observed in autozooids, visible as a series of concentric orificial rims ( Fig. 7E ).

Remarks. There is a discrepancy in the number of colonies and related depth ranges between the material currently available in the SMNH collection and the batches of specimens mentioned in Silén (1947). Silén listed 21 specimens from 150–375 m depth, 11 from 300–450 m depth, and two from 450–600 m depth, while the syntypes studied here include 13 colonies reported from a depth of 366–546 m, and eight colonies collected at 182– 455 m. Another discrepancy is related to the year of collection, which is reported as 1861 by Silén (1947) but 1869 on the specimen labels. The colony figured in Silén (1947, pl. 4, fig. 24) in addition of not being identifiable among the specimens available, also lacked both the large spatulate avicularia and ovicells, which were instead described and drawn in his text-figs 47 and 48, making it, even if identifiable, not the ideal candidate as the type specimen. Based on the above-mentioned reasons, a lectotype (SMNH-128088a) is here designated, based on the best preserved colony, as well as the most complete character-wise ( Fig. 7A–C ).

In the original description, Silén (1947) considered each colony as an internode and speculated that the colony itself was made of several internodes connected by tubes. There are neither direct observations nor morphological characters supporting this hypothesis. The original record is the only one available for this species and the genus is also monospecific. However, based on observations of other genera with similar colony-form (e.g. Fedora in Ascosiidae ), it seems more likely that each colony was independent and rooted to the substrate by rhizooids or a chitinous tube.

Cook & Lagaaij (1976) listed Fedorella among conescharelliniform genera, i.e. colonies with frontally budded zooids with reversed orientations. Gordon & d’Hondt (1997) rejected this statement based on the description and illustrations already provided in Silén (1947) and confirmed here.

Figures

FIGURE 6. Fedorella minima Silén, 1947, Anguilla. A, B. Paralectotype SMNH-Type-8734a. A. General view of the colony. B. Close-up of a zooid with paired avicularia, one small and triangular, the other one giant and spathulate. C. Paralectotype SMNH-Type-8734b, general view of the colony with zooids having single avicularium. D. Paralectotype SMNH-Type-8734c, group of zooids, some with paired distolateral, oral spine bases (arrowed) and a kenozooid (asterisk). Scale bars: A, C = 500 µm; B = 200 µm; D = 300 µm.

FIGURE 7. Fedorella minima Silén, 1947, Anguilla. A–C. Lectotype (designated here) SMNH-128088a. A. General view of the colony. B. Group of zooids, showing avicularian variability, the shape of the orifice and opercula. C. Close-up of a zooid with paired giant avicularia and lateral view of an ovicell. D. Paralectotype SMNH-128088b, group of ovicellate zooids showing the triangular opening of the ooecium. E, F. Paralectotype SMNH-128088c. E. Close-up of two zooids with only one or completely lacking avicularia; the orifice of the zooid on the left shows signs of repetitive intramural budding. F. Close up of an orifice with closure plate. Scale bars: A = 500 µm; B, D = 300 µm; C, E = 200 µm; F = 100 µm.