Setosella vulnerata ( Busk, 1860 )

Souto, Javier, Berning, Björn & Ostrovsky, Andrew N., 2016, Systematics and diversity of deep-water Cheilostomata (Bryozoa) from Galicia Bank (NE Atlantic), Zootaxa 4067 (4), pp. 401-459 : 416-419

Setosella vulnerata ( Busk, 1860)

( Figs 33–38 , Table 8 )

Membranipora vulnerata Busk, 1860: 124 .

Setosella vulnerata: Hincks 1880: 181 , pl. 21, fig. 7; Harmelin & d’Hondt 1992: 28; Hayward & Ryland 1998: 298, fig. 103; De Blauwe 2009: 252, figs 257, 258.

Setosella sp.: Reverter-Gil et al. 2012: 164 , fig. 4.

Material examined. Lectotype (designated here): NHMUK 1899.7.1.1487, Micropora vulnerata , Shetland, Barlee/Busk Coll., dry, type. Paralectotypes (designated here): NHMUK 1911.10.1.760, Setosella vulnerata , Shetland, Barlee/Busk Coll., dry, type (6 colonies). Other material examined: MNCN 25.03/3937, locality V01.

Description. Colony encrusting, unilaminar, forming a small discoidal patch of alternating autozooids and vibracula on a sand grain. Autozooids irregularly oval to sub-rhomboidal, with well-developed smooth gymnocyst proximally that narrows and steepens distally, lateral walls slightly raised, framing an evenly granular cryptocyst that is flat and depressed proximally, gently rising distal to the opesiules to form proximal border of opesia. Opesia D-shaped, slightly wider than long, distal margin with narrow immersed lunula formed by numerous blunt denticles. Two elongated, usually slit-like opesiules in distal depressed area of cryptocyst, positioned near lateral walls of zooid, their inner edges bearing fine denticles; length of opesiules generally unequal, the left opesiule usually being longer.

Small interzooidal, vibraculoid avicularia oval, placed distal or distolateral to each autozooid, with wide oval to reniform opesia, slightly narrower in middle; seta long and slender, up to twice length of autozooid, curved.

SD, standard deviation; N, number of measurements

Ovicells terminal, with brood cavity immersed within distal part of maternal zooid. Kenozooidal ooecium roughly level with colony surface, forming shallow hood covering distal end of maternal zooid from which it is budded. Proximal ooecial margin forming distal part of zooidal orifice; ectooecium with oval membranous window and granular endooecial surface underneath. Ovicellate zooids dimorphic, usually distally wider and shorter than autozooids, with orifice distinctly broader and campanulate in outline. Distal budding of autozooids and vibracula in ooecium-producing zooid retained.

Ancestrula oval, half size of autozooid; cryptocyst relatively smooth, occupying slightly more than half of frontal area, opesia campanuliform. Astogenesis beginning with 2 disto-lateral autozooids, each generating a clockwise spiral series surrounding ancestrula, with the autozooid size increasing gradually; later zooids more irregularly arranged.

Remarks. When revising NE Atlantic and Mediterranean material, Reverter-Gil et al. (2012) suggested that more than one species was reported under the name Setosella vulnerata (Busk) in the literature. Examination of the type of S. vulnerata , and of specimens on which the descriptions of several authors are based (e.g. Prenant & Bobin 1966; Zabala & Maluquer 1988; Hayward & Ryland 1998), is required to resolve this problem. Also, owing to the few morphological characters present, and the existence of only slight differences between populations, genetic analysis will be needed to define the northern and southern limits of distribution of this/these species.

A revision of the species complex is beyond the scope of this paper, but in order to initiate this process and to fix the status of Setosella vulnerata Busk (1860) we have here re-described and designated a lectotype (NHMUK 1899.7.1.1487) and paralectotypes (NHMUK 1911.10.1.760) from the type locality, the Shetland Islands. The types are also imaged using SEM for the first time ( Figs 37, 38 ). Comparison between specimens is hindered by the fact that the lectotype is not bleached, and that certain skeletal characters are absent from the analysed paralectotype. For instance, the exact shape of the ancestrular opesia could not be observed, while Hayward & Ryland (1998, fig. 103B) depicted an oval opesia in a British non-type specimen. For a thorough revision, resampling of the type locality will therefore be necessary.

Apart from slightly coarser granulation of the cryptocyst, our single colony from Galicia Bank does not seem to be distinctly different from the type of S. vulnerata in morphology or morphometrics. Although the window in the ooecium also seems to be larger than in S. vulnerata , this may simply be due to the fact that the only maternal zooids in our specimen are young and situated at the colony margin, whereas it can be observed in Setosella species generally that the size of the window is reduced with age (J. Souto pers. observ.).

Our specimen also largely corresponds with the material described by Reverter-Gil et al. (2012, fig. 4), although in their figured specimen from off SW Portugal the opercular shelf (lunula) in the distal orifice margin appears slightly broader whereas in our specimen it is narrower. Also, the ancestrula in our specimen is distinctly larger (0.315 mm) than that (0.266 mm) reported by Reverter-Gil et al. (2012). Whether these characters reflect intra- or interspecific differences has to be determined in a separate study.

The only colony collected from Galicia Bank encrusted a small sand grain at 867 m depth.

Figures

FIGURES 33 – 38. Setosella vulnerata (Busk, 1960 a): 33, general view of specimen from Galicia Bank (MNCN 25.03 / 3937); 34, autozooids at colony periphery colony (MNCN 25.03 / 3937); 35, autozooids with ovicells and vibracula (MNCN 25.03 / 3937); 36, ancestrula (MNCN 25.03 / 3937); 37, general view of colony (lectotype, NHMUK 1899.7.1.1487); 38, part of a bleached colony (paralectotype, NHMUK 1911.10.1.760).

Tables

TABLE 8. Measurements (in mm) of Setosella vulnerata.

	Mean	SD	Minimum	Maximum	N
Autozooid length	0.388	0.0287	0.341	0.424	9
Autozooid width	0.232	0.0206	0.198	0.264	9
Opesia length	0.069	0.0032	0.063	0.072	9
Opesia width	0.081	0.0083	0.066	0.089	9
Vibraculum length	0.083	0.0045	0.079	0.089	4
Vibraculum width	0.054	0.0018	0.052	0.056	4
Ancestrula length	0.315				1
Ancestrula width	0.216				1
Ancestrular opesia length	0.123				1
Ancestrular opesia width	0.103				1