Microeciella suborbicularis ( Hincks, 1880 )

Taylor, Paul D. & Zatoń, Michał, 2008, Taxonomy of the bryozoan genera Oncousoecia, Microeciella and Eurystrotos (Cyclostomata: Oncousoeciidae), Journal of Natural History 42 (39 - 40), pp. 2557-2574 : 2570-2572

publication ID	https://doi.org/ 10.1080/00222930802277640
persistent identifier	https://treatment.plazi.org/id/734087F6-B909-3674-FE19-FBA813EEFD9C
treatment provided by	Felipe
scientific name	Microeciella suborbicularis ( Hincks, 1880 )
status

Treatment

Microeciella suborbicularis ( Hincks, 1880) View in CoL

( Figures 5D–F View Figure 5 ; 7A–G View Figure 7 )

Diastopora suborbicularis Hincks 1880, p. 464 , Plate 66, Figures 11, 11a.

?non Microecia suborbicularis (Hincks) : Harmelin 1976, p. 122, Plate 8, Figures 1 View Figure 1 , 2 View Figure 2 , Plate 17, Figures 4 View Figure 4 –8.

Eurystrotos compacta (Norman) View in CoL : Hayward and Ryland 1985a, p. 1074, Figure 1A, B View Figure 1 ; Hayward and Ryland 1985b, p. 94, Figure 32A–D;?Zabala and Maluquer 1988, p. 171, Figures 525–526;? Hayward and McKinney 2002, p. 116, Figure 55F–H.

Material

Lectotype. NHM 99.5.1.1427a, Isle of Man, Hincks Collection. The ‘‘type slide’’ comprises a large bivalve fragment encrusted by two colonies, of which the largest ( Figure 1D View Figure 1 ) is chosen here as the lectotype, a third colony on a separate smaller shell fragment, and a piece of a colony mounted upside down. The remaining three colonies (99.5.1.1427b-d) are paralectotypes.

Other material. NHM 11.10.1.166, Salcombe, Devon, gold-coated specimen figured by Hayward and Ryland (1985b, Figure 32A). NHM 1984.12.26.34, southern Irish Sea, gold-coated specimen figured by Hayward and Ryland (1985a, Figure 1A, B View Figure 1 ; 1985b, Figure 32B, C). NHM 2001.1.26.5, Western Channel, UK, comprising about 20 colonies, at varying stages of development, encrusting the interior of a Glycymeris shell.

Description

Colony encrusting, small to moderate in size, maximum observed diameter 11 mm, multiserial, initially fan-shaped ( Figure 5D View Figure 5 ), becoming discoidal with a circumferential growing edge ( Figures 1D View Figure 1 ; 7F View Figure 7 ). Ancestrula partly or completely overgrown by later zooids ( Figure 7A View Figure 7 ); protoecium ( Figure 5F View Figure 5 ) visible in young colonies, about 0.12–0.13 mm in diameter, with very sparse, scattered pseudopores; distal tube elongate, about 0.21–0.28 mm long by 0.07–0.09 mm wide, straight or curved to one side distally ( Figure 5E View Figure 5 ), aperture longitudinally elliptical, 0.08 by 0.05 mm. Growing edge low, usually only one generation of zooids visible at budding zone, distal fringe of exposed basal lamina narrow.

Autozooids elongate, frontal walls 0.39–0.59 mm long by 0.11–0.15 mm wide, flat proximally, gently convex distally; pseudopores ( Figure 7G View Figure 7 ) broad teardrop-shaped, pointed distally, without spines, small, 4–5 mm wide. Apertures circular or longitudinally elongate, small, 0.06–0.10 mm long by 0.06–0.08 mm wide, arranged more or less quincuncially, peristomes low; terminal diaphragms closing some apertures, pseudoporous.

Gonozooids ( Figure 7B–E View Figure 7 ) frequently present, in one or more generations, proximal frontal wall short or moderate in length, indistinguishable from an autozooid, brood chamber ovoidal to pyriform, elongate, 0.54–0.77 mm long by 0.30–0.42 mm wide, low in profile, outline indented by apertures of neighbouring autozooids, roof densely pseudoporous, the pseudopores diminishing in number distally, proximal edge of brood chamber roof sometimes draped back over proximal frontal wall ( Figure 7C, E View Figure 7 ). Ooeciopore terminal, rarely subterminal ( Figure 7D View Figure 7 ), smaller than an autozooidal aperture, transversely elliptical to subcircular, 0.06– 0.07 mm in diameter; ooeciostome short, straight or curved proximally.

Remarks

Hayward and Ryland (1985a, 1985b) followed Harmelin (1976) in considering Diastopora suborbicularis Hincks, 1880 to be a junior synonym of Alecto compacta Norman, 1867 , a species here placed in synonymy with Oncousoecia dilatans ( Johnston, 1847) . However, this synonymy can be rejected following study of the type material of D. suborbicularis and A. compacta . Apart from differences in colony form (subcircular sheets versus branched), the most striking contrast is seen in the ancestrula. In O. dilatans this has a short distal tube and a large protoecium with a single row of minute pseudopores around its perimeter ( Figure 5A–C View Figure 5 ). The ancestrula of Microeciella suborbicularis has a long distal tube and a relatively small protoecium with extremely few pseudopores not arranged perimetrically ( Figure 5D–F View Figure 5 ). Weedon (1998) made a comparative study of the early astogeny of cyclostomes, finding that some species lacked pseudopores on the protoecium whereas in others they were distributed over the entire surface or confined to the rim. Although not traditionally used in cyclostome taxonomy, such differences are likely to be significant for distinguishing species and supraspecific taxa.

The identity of supposed examples of Microeciella suborbicularis from the Mediterranean is uncertain. Illustrations of the gonozooids in Mediterranean colonies often show them to be short and subtriangular in outline with a straight distal edge ( Harmelin 1976, Plate 8, Figure 1 View Figure 1 ; Hayward and McKinney 2002, Figure 55G) in contrast with the long, ovoidal gonozooids of M. suborbicularis from the type and other eastern North Atlantic localities.

While some doubts remain about the placement of this species in Microeciella because of the terminal position of the ooeciopore as opposed to its subtermianl location in the type species, this feature may not have great importance. Gonozooids in M. suborbicularis occasionally have subterminal ooeciopores ( Figure 7D View Figure 7 ), while Jurassic species attributed to Microeciella often have terminal ooeciopores.