Conescharellina brevirostris 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 : 78-81

Conescharellina brevirostris Silén, 1947a

( Fig. 42 ; Table 37)

Conescharellina brevirostris Silén, 1947a: 39 , text-figs 24, pl. 1, figs 4–6.

Material examined. Syntypes: SMNH-Type-4604 (four colonies), Java Sea, Noordwachter Island, Malay Archipelago ; 2°56'S, 107°55'E; depth 15–18 m. Leg. C. Aurivillius 1891 .

Other material: Holocene , Core 19, sample 19053, 52–53 cm core depth, Daidokutsu submarine cave, Ie Island, Okinawa, Japan; 26.72°N, 127.83°E; water depth 29 m ( Fig. 43 , Table 38) .

Description. Colony small, conical, flattened, height 1.238 –1.284 mm and basal diameter 1.264 –1.605 mm in the syntypes ( Fig. 42 ), height 1.200 mm and basal diameter 1.378 mm in the Holocene specimen ( Fig. 43 ), with 12–18 slightly prominent, narrow, radial costules corresponding with the raised peristomes of the autozooids, alternating with intercostular valleys occupied by rows of interzooidal avicularia ( Figs 42A, E , 43A ).

Autozooids arranged in radial rows corresponding to the prominent costules, with four autozooids per row; orifices of autozooids in the same costule vertically aligned but alternating with orifices of autozooids in neighbouring costules; autozooids of the antapical surface somewhat elliptical, almost as long as wide (mean L/ W 0.94 in the syntypes; 1.072 in the Holocene specimen); interzooidal communication through small, circular, uniporous pore-chamber windows, 2–4 along each lateral margin of the zooids, 8–18 µm in diameter ( Fig. 42C ). Frontal shield convex around the orifice, flat centrally, smooth, nodular, imperforate except for one or two elliptical marginal areolar pores (10–15 µm in maximum diameter) placed laterally ( Fig. 43B ).

Primary orifice with semielliptical anter (mean L/ W 1.28) and rounded triangular condyles, 8–10 µm long, pointing medio-distally and defining a shallow U-shaped sinus ( Figs 42B , 43B ); apical pore absent; peristome collar-like, well developed laterally and proximally ( Figs 42B, C , 43A, B ), forming a proximal concave shelf about 25–30 µm wide, absent or little developed distally.

Interzooidal avicularia circular arranged in radial, sinuous or linear rows along the furrows between costules, with 6–8 avicularia per row, rostrum slightly raised, randomly directed, either distolaterally or proximolaterally, crossbar complete ( Figs 42D , 43B ). An additional adventitious avicularium only in some autozooids, placed distolaterally to the orifice, lying on the peristome, elliptical, with blunt triangular rostrum directed proximolaterally, and with complete crossbar ( Figs 42A, E , 43A, B see arrows).

Apical surface coarsely tubercular, occupied by kenozooids and avicularia ( Fig. 42F, G ); antapical surface ( Fig. 42I–J ) with kenozooidal pits and avicularia in radial rows, continuous with those of the lateral surface of the colony, and centrally.

Ovicells not observed.

Remarks. Silén (1947a, p. 39) examined 48 colonies of Conescharellina brevirostris from the Java Sea off Noordwachter Island in the Malaysian Archipelago, all presumably dead when collected based on the poor preservation and the total lack of organic tissues and appendages, such as rhizoids and mandibles. Only four syntypes were available for examination. Given the possibility that the remaining syntypes mentioned by Silén (1947a) might be better preserved and found later in the SMNH collection or elsewhere, the designation of a lectotype for this species is avoided.

The co-occurrence of the collar-like peristome and the presence of an avicularium close to the orifice distinguish this species from its congeners described from Noordwachter Island. The broken ovicell described by Silén (1947a) was not observed in the colonies available.

A colony of C. brevirostris ( Fig. 43 ) was also found in a Holocene sediment core, dated c. 2000 years (see Chiu et al. 2016, 2017), taken from the Daidokutsu submarine limestone cave off Ie Island, Okinawa, Japan.

Figures

FIGURE 42. Conescharellina brevirostris Silén, 1947a. SMNH-Type-4604, Java Sea, Malay Archipelago. A, E. Lateral views of two colonies. Arrows indicate adventitious avicularia placed distolaterally to the orifice in some zooids. B. Close-up of a zooid with surrounding interzooidal avicularia. C. Close-up of an orifice showing the proximolaterally developed peristome. D. Close-up of an avicularium. F. Apical view of a colony. G. Close-up of the apical kenozooids. H. Antapical view of a colony. I, J. Close-ups of the antapical surface and avicularia. Scale bars: A, E, F, H = 500 µm; B, C = 100 µm; D = 200 µm; G, I = 300 µm; J = 50 µm.

FIGURE 43. Conescharellina brevirostris Silén, 1947. Daidokutsu submarine cave, Ie Island, Okinawa, Japan. A. Lateral view of the colony. Arrows indicate adventitious avicularia placed distolaterally to the orifice in some zooids. B. Close-up of a zooid with surrounding interzooidal avicularia. The arrow indicates the adventitious avicularium distolaterally to the orifice. C. Antapical view of a colony. D. Close-ups of the central antapical surface with avicularia. Scale bars: A, C = 200 µm; B = 100 µm; D = 100 µm.