Conescharellina laevis Silén, 1947a

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 : 81-83

Conescharellina laevis Silén, 1947a

( Fig. 44 ; Table 39)

Conescharellina laevis Silén, 1947a: 42 , text-figs 26, 27, pl. 1, figs 9, 10.

Material examined. Lectotype (designated here) SMNH-Type-4606a ( Fig. 44A–C ), Java Sea, Noordwachter Island, Malay Archipelago ; 2°56'S, 107°55'E; depth 15–18 m. Leg. C. Aurivillius 1891 . Paralectotypes SMNH-Type-4606b ( Fig. 44D, E ), SMNH-Type-4606c ( Fig. 44F ), and SMNH-Type-4606d ( Fig. 44G ), same details as lectotype.

Description. Colony small, conical, height 1.45 mm and basal diameter 1.49 mm in the lectotype ( Fig. 44A ), height 1.67 mm and basal diameter 1.44 mm in the largest paralectotype ( Fig. 44D ), with 12–16 slightly prominent, narrow, radial costules corresponding with the raised, lateral margins of the autozooids and the rows of interzooidal avicularia, alternating with very shallow, intercostular valleys occupied by autozooidal orifices ( Fig. 44A, D, E ).

Autozooids arranged in alternating radial rows, with 5–6 zooids per row; autozooids of the antapical surface somewhat elliptical, slightly longer than wide (mean L/ W 1.16). Frontal shield raised at the margins and sloping gently towards the centre, smooth, nodular, imperforate except for one or two circular marginal areolar pores (6–8 µm in diameter) proximomedially placed ( Fig. 44B, C ).

Primary orifice depressed in relation to the adjacent surface and surrounded by a smooth band of calcification, 5–15 µm wide, circular (mean L/ W 1.02) with rounded triangular condyles, 6–10 µm long, pointing distally and defining a shallow U-shaped sinus ( Fig. 44C ); a distal circular to elliptical ooecial pore, 8–12 µm in maximum diameter, associated with each orifice (although sometimes obliterated), outlined by a semicircular to semielliptical rim, 5–10 µm wide, of smooth calcification as that of the orifice, its proximal margin continuous with part of the distal margin of the band of calcification encircling the orifice ( Fig. 44B, C, E ).

Interzooidal avicularia arranged in radial, sinuous rows, with 8–12 avicularia per row, in a way that each zooid is surrounded by six avicularia, one at each corner (two proximally, two mid-laterally and two distally) outlining a hexagon, circular; rostrum semi-circular, obliquely directed either distolaterally or proximolaterally, crossbar complete ( Fig. 44B, C, E ).

Apical surface usually poorly preserved, tubercular, chaotically occupied by kenozooids and avicularia ( Fig. 44D, F ); antapical surface ( Fig. 44G ) pitted and with radial rows of avicularia continuous with those of the lateral surface of the colony.

Ovicells not observed.

Remarks. Of the nine colonies mentioned by Silén (1947a), only four were available in the collection.Although the lot of specimens was catalogued as holotype (i.e. SMNH-Type-4606- holotype), it includes multiple colonies with no univocal designation of the holotype colony neither in Silén (1947a) nor in the physical specimen box. Consequently, the best preserved syntype has been selected as the lectotype ( Fig. 44A–C ). This specimen seems to correspond in colony size and shape with that figured by Silén (1947a, fig. 9).

The absence of a well-developed tubular peristome distinguishes this species from other congeners from Noordwachter Island in the Java Sea, i.e. C. brevirostris and C. longirostris .

Five species of Conescharellina were described from Indonesia by Harmer (1957). Conescharellina distalis , C. ovalis , C. papulifera and C. rectilinea all differ in having a well-develop tubular or bisinuate peristome. Conescharellina symmetrica is the most similar to C. laevis in having colonies of similar height and width, in the absence of a tubular peristome, and in the zig-zag arrangement of avicularia outlining distinctly a hexagon ( Harmer 1957, p. 97, fig. 72); the main difference between the two species, based on Harmer’s (1957) description, is the shape of the orificial sinus, which is described as subtriangular in C. symmetrica while is U-shaped in C. laevis .

Three additional species of Conescharellina are known from the Indo-Pacific: C. catella Canu & Bassler, 1929 differs in having a laterally well-developed peristome (see Hirose 2011, fig. 1); C. crassa ( Tenison Woods, 1880) has laterally raised and distally prominent peristomes as well as avicularia with a ligula ( Bock & Cook 2004); C. dilatata d’Orbigny, 1852 is characterised by a porous area, interpreted as cancelli by Bock & Cook (2004), on the antapical surface.

Figures

FIGURE 44. Conescharellina laevis Silén, 1947a. Java Sea, Malay Archipelago. A–C. Lectotype (designated here) SMNH- Type-4606a. D, E. Paralectotype SMNH-Type-4606b. F. Paralectotype SMNH-Type-4606c. G. Paralectotype SMNH-Type- 4606d.A, D. Lateral views of two colonies. B. Group of zooids. C. Close-up of orifices and avicularia. E. Close-up of two rows of autozooids and avicularia. F.Apical view of a colony with the zone of kenozooids. G. Antapical view of a colony with radial rows of avicularia between autozooids. Scale bars: A, D, F, G = 500 µm; B, E = 300 µm; C = 100 µm.