Stenopsella fenestrata ( Smitt, 1873 )

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 : 173-175

Stenopsella fenestrata ( Smitt, 1873)

( Fig. 9 ; Table 7)

Hippothoa fenestrata Smitt, 1873: 47 , pl. 6, fig. 142.

Stenopsella fenestrata: Bassler 1952: 385 .

Material examined. Holotype by monotypy SMNH-Type-1800, North Atlantic Ocean , S of Tortugas, United States, depth 31 m. Leg. Gulf Stream Explorations 1868–69.

Description. Colony encrusting, multiserial, unilaminar ( Fig. 9A ).

Autozooids distinct with deep interzooidal furrows, salient, quincuncially or irregularly arranged, hexagonal or rhomboidal, longer than wide (mean L/ W 1.44)

Frontal shield convex, finely granular and crenulated in young zooids at colony growing edge ( Fig. 9D ) but developing spinose frontal processes in older generations of autozooids ( Fig. 9C ), evenly and densely perforated, up to four-fifth of its length corresponding to the attachment line of the peristome; pseudopores circular, minute, 8–10 µm in diameter; marginal areolae undistinguishable.

Primary orifice subcircular with pointed triangular condyles separating a quadrangular anter from a shallow, bowl-shaped sinus ( Fig. 9D ), usually hidden by a tubular, imperforate peristome, directed upwards and frontally, forming a transversely elliptical secondary orifice, about 200 µm long by 300 µm wide ( Fig. 9C, D ); spiramen placed at the base of the peristome at the end of a short tube with a more or less flared rim, transversely elliptical or reniform, 170–215 x 75–95 µm, facing frontally or downwards ( Fig. 9B, C ).

Avicularia single or paired, placed at the base of the peristome, drop-shaped with rounded, slightly raised rostrum directed distolaterally and inwards, and complete crossbar ( Fig. 9D, E ).

Ovicells and ancestrula not observed.

Remarks. Smitt (1873) placed this species in Hippothoa Lamouroux, 1821 acknowledging that the small encrusting colony (in agreement with the syntype illustrated here) available from Pourtales’ collection lacked the most essential character of the genus, i.e. the orificial sinus. However, the observation of such a sinus on an erect fragment of what he thought was the same species but collected in the Pacific and housed at the British Museum (i.e. NHMUK), prevented him from creating a separate genus for the western Atlantic specimen.

A new genus, Stenopsis , was first mentioned in Canu & Lecointre (1925) as a nomen nudum and subsequently formally introduced in Canu & Bassler (1927) with type species Smitt’s H. fenestrata . The name Stenopsis was preoccupied by Stenopsis Rafinesque, 1815 (a beetle of the family Tenebrionidae ), and Bassler (1952) coined the replacement name Stenopsella to include, in addition to Smitt’s species, two fossil species from the Eocene of North America initially identified as Galeopsis Jullien, 1903 in Jullien & Calvet (1903) by Canu & Bassler (1920).

However, Stenopsella seems to match the definition of Gigantopora Ridley, 1881 in having encrusting colonies, salient autozooids with nodular frontal shields pierced by pseudopores, a tubular peristome directed upwards and outwards, single or paired avicularia on the sides of the peristome, and a special roundish, transversely broad pore visible frontally ( Ridley 1881, p. 47). The ooecium of the type species is also described as “small, globose, recumbent at back of cell proper, punctate” ( Ridley 1881). Although Smitt’s syntype lacks ovicells, they can be seen in the SEM image of a Gulf of Mexico specimen taken by J.E. Winston and available at http://bryozoa.net/cheilostomata/ gigantoporidae/stenopsella_fenestrata.html ( Bock 2022). The cap-like, perforated ooecium corresponds with the description of that in the type species but also with those of the numerous Recent and fossil species of Gigantopora . Based on these observations, Stenopsella is here proposed as junior synonym of Gigantopora , and the new combination Gigantopora fenestrata suggested. Judging by the images and description available in Canu & Bassler (1920), it is likely that both Eocene species currently attributed to Stenopsella , i.e. S. cyclops and S. longicollis , should also be placed in Gigantopora . In addition, some of the species in Canu & Bassler (1920) currently attributed (some tentatively) to Galeopsis , i.e. G. erinaceus , G. convexa and G. verrucosa appear to have pseudoporous frontal shields and, therefore, might better fit into Gigantopora as well.

Figures

FIGURE 9. Stenopsella fenestrata (Smitt, 1873), Holotype SMNH-Type-1800, Tortugas, United States, here proposed as Gigantopora fenestrata comb. nov. A. General view of the colony. B. Group of zooids some in frontal and other in lateral view. C. Close-up of some zooids in lateral view, showing the development of the peristome, a variable position of the avicularium in relation to the spiramen, and the prickly appearance of the frontal shield. D. Close-up of a zooid with broken peristome and showing the primary orifice. E. Close-up of the adventitious, peristomial avicularium with complete crossbar. Scale bars: A = 1 mm; B, C = 500 µm; D = 300 µm; E = 100 µm.