Setosella cavernicola Harmelin, 1977

Rosso, A., Martino, E. Di & Gerovasileiou, V., 2020, Revision of the genus Setosella (Bryozoa: Cheilostomata) with description of new species from deep-waters and submarine caves of the Mediterranean Sea, Zootaxa 4728 (4), pp. 401-442 : 415-420

Setosella cavernicola Harmelin, 1977

( Figs 8a, b , 9–12 ; Tables 1 , 2 , 4 )

Setosella vulnerata ( Busk, 1860) : Harmelin, 1969: table 1 (pars).

Setosella cavernicola Harmelin, 1977: 1064 , fig. 17; tav. 1, fig. 7 (pars).

? Setosella cavernicola: Harmelin, 1979 (listed); Zabala, 1986: 299, fig. 82c.

Setosella cavernicola: Rosso et al., 2013a : table 17.1 (pars); Rosso et al., 2013b: table 1 (pars).

Setosella sp. 1: Rosso et al., 2019a: table 1; Rosso et al., 2019b: table 1, fig. 1a.

Examined material. SEM micrographs of the colony MNHN _IB_2008-13068 supposedly designated as the holotype by Harmelin himself when depositing the material at MNHN, and provided by Pierre Lozouet; Rosso Collection. PMC. R.I.H. B-13a. Gymnasium cave, c. 20 m depth, GM2s, c. 35 m from the entrance, four dead colonies each consisting of 3–5 zooids on small biogenic clasts; GM3s, c. 55 m from the entrance, one dead colony of 4 zooids; Mazzere cave c. 20 m depth, MZ 2s, c. 35 m from the entrance, one dead fragment. Granchi cave, GR1P, c. 20 m depth and 10 m from the entrance, seven live colonies on bioeroded concretions, often including the ancestrula and fertile zooids, one of which on the same substratum as the holotype of S. rossanae n. sp. Plemmirio MPA, SE Sicily. Rosso Collection PMC. R.I.H. B-13b. Fara cave, Lesvos Island, 11–18 m depth: FC2, 15– 20 m from the entrance (10 live and six dead colonies); F4, 20– 30 m from the entrance (17 live and nine dead colonies); Agios Vasilios cave, Lesvos Island, 24–40 m depth: VC2, 15– 20 m from the entrance (one dead colony); V 2, 15 – 20 m from the entrance (one live and one dead colony).

Additional material. SEM micrographs of two (out of six) colonies stored at MNHN, catalogue number MNHN _IB_2013-998, as Setosella cavernicola , but belonging to different species, and provided by Pierre Lozouet.

Description. Colony encrusting, unilaminar, forming irregular, uneven patches occupying a few mm 2, usually in the cavities of organogenic concretions ( Figs 9a , 10a , 11a ). Autozooids quincuncially arranged ( Figs 10e, f , 12a, c, d ), elongate rhomboidal, the maximum width reached at about mid-length ( Fig. 12c ). Gymnocyst largely exposed laterally and proximally, gently sloping, outlining a basal surface significantly larger than the frontal one. Proximal end elongate, wedged between proximal zooids, sometimes forming a short cauda-like ( Fig. 10e ). Frontal area ovoidal, marked by a raised, thin and smooth rim, often accounting for nearly two-thirds of the zooidal width. Cryptocyst finely granular, occupying nearly three-fourths of the frontal area, depressed and relatively flat, with a steep edge, slightly raising distally to form the slightly concave proximal border of the opesia. Opesia nearly bellshaped ( Figs 9a , 11c , 12b ), slightly wider than long, with a distal shelf formed by 5–8 slightly prominent tubercles situated in the central arched portion, keeping the operculum in closure position. Spines absent. A single pair of large, c. 30–35 µm wide, roundish-to-slightly elongate, smooth-sided, lateral opesiules inserted on the steep margin of the cryptocyst, at about 40 µm from the proximal margin of the opesia ( Figs 10d , 11c , 12b ). One large uniporous septulum, at nearly mid-length, in each lateral zooidal wall. Interzooidal vibracula circular to ovoidal, placed distally to each autozooid ( Figs 9 b–d, 10e, 11c, d, 12b, c), with two small uniporous septula proximo-laterally, later communicating with distolateral autozooids; opesia ovoidal to eight-shaped, laterally marked by two slightly asymmetrical blunt constrictions bearing barely developed, proximally directed indentations; rostrum arched and flared; vibracular seta about twice as long as an autozooid. Ovicell produced by the maternal autozooid, visible distally to the orifice as a crescent-shaped, low prominence; ectooecium smooth, with a median, circular (less than 20 μm in diameter), infundibular pseudopore ( Figs 9b, d , 10e, f , 11c ). Ancestrula oval, smaller than autozooids ( Figs 9c , 10b , 11e ); cryptocyst smooth with faint growth lines, occupying the proximal half of the frontal area and leaving a wide semi-elliptical opesia; typically buddying a hourglass-shaped kenozooid distally ( Fig. 11e ) budding in turn a small vibraculum distally, and a large vibraculum disto-laterally on the left side of the ancestrula, orthogonally oriented. Occlusion plates observed in some vibracula ( Fig. 11a, d ).

Remarks. Setosella cavernicola was introduced by Harmelin (1977) to distinguish colonies from Trémies submarine cave (near Cassis, Marseille, France) previously attributed to S. vulnerata ( Harmelin 1969) from true colonies of this species collected at Concepcion Bank (Canary Islands). Harmelin (1977, fig. 17) distinguished the new species based on the smaller colony size, the slightly granular cryptocyst and the rounded morphology of the opesiules. These diagnostic characters can also be observed in the colony deposited at MNHN, catalogue number MNHN_IB_2008-13068 ( Fig. 8a, b ), and indicated as the holotype in the MNHN web collection database (accessible at https://science.mnhn.fr/institution/mnhn/collection/ib/item/2008-13068?listIndex=2&listCount=37; accessed 19.11.2019), although Harmelin (1977) does not provide any information on the type material.

In addition, Harmelin (1977, fig. 16) illustrated a group of zooids with four opesiules, stating that the number of opesiules can double in some colonies. The two illustrations also differ in the position of the vibraculum with respect to the autozooid, placed distolaterally in fig. 16 and distally in fig. 17. Four opesiules and disto-laterally placed vibraculum characterise one of the colony ( Fig. 8c, d ), out of six, deposited at the MNHN, catalogue number MNHN_IB_2013-998 (accessible at https://science.mnhn.fr/institution/mnhn/collection/ib/item/2013-998?listInde x=3&listCount=37; accessed 19.11.2019). Both the number of opesiules and position of vibracula are constant within colonies in the type series as well as in the material examined for this study. Consequently, we separate the two species: S. cavernicola Harmelin, 1977 with holotype MNHN_IB_2008-13068 ( Fig. 8a, b ) and we introduce a new species, S. rossanae n. sp. (described below), to which we attribute the colony in MNHN_IB_2013-998 figured here ( Fig. 8c, d ). Zabala (1986, fig. 82A) illustrated the co-occurrence of two, four and five equidimensional opesiules in different autozooids in the same colony with inconstant vibracula always placed distolaterally to autozooids, which it is likely to be a mixture of characters observed in several different colonies as also proved for other bryozoan species (e.g. Rosso 1999).

Setosella cavernicola appears well characterised, and easily distinguishable from all congeners, based on its two, large-sized, circular opesiules and distal vibraculum coaxial with the associated proximal autozooid, and narrow ooecium lacking a window but with a small frontal pseudopore. Setosella folini also has a distally placed vibraculum coaxial with the associated proximal autozooid but differs in having free-living, ring-shaped colonies and slit-like opesiules.

Setosella cavernicola autozooids are variable in size and shape.Although the size of autozooids rapidly increases in the zone of astogenetic change like in other congeners, the size of vibracula appears to be constant. Autozooidal shape seems to change remarkably in S. cavernicola probably because it encrusts particularly uneven surfaces in cavities of concretional walls and ceilings of submarine caves. In this habitat, S. cavernicola has been found in the inner dark recesses and in the transition zone between dark and semi-dark cave sectors ( Harmelin 1969; Rosso et al. 2019 a, 2019b), where food supply is limited. Colonies reach a relatively large size (2–3 mm in diameter) and often autozooids show evidence of multiple regenerations with intramural buds visible as series of mural/oral rims. Up to seven distal oral rims have been counted, and as many roughly concentric, mural rims of superimposed cryptocystal layers, progressively shifting distally up to the autozooid mid-line ( Fig. 11a, c ). In these repeatedly regenerated autozooids, the opesia becomes smaller and irregularly shaped. Regenerations have also been observed in some ovicells and vibracula, although more rarely. Regenerations also occur following breakage of autozooids at any point along walls. All these features suggest that colonies persist for long time and are able to ‘self-repair’.

Distribution. Setosella cavernicola is presently known mostly from submarine caves. First reported ( Harmelin 1969, 1977) from the dark recesses of the Trémies cave near Marseille (about 6 m depth), it has repeatedly been cited from the same area ( Harmelin 1986, 2000), and new colonies were more recently found in submarine caves of the eastern Mediterranean. Setosella cavernicola is common in the Plemmirio Peninsula, Syracuse, eastern coast of Sicily, W Ionian Sea, and the Lesvos Island, NE Aegean Sea ( Rosso et al. 2019 a, 2019b, as Setosella sp. 1), in all the caves sampled at date (three and two, respectively). However, following the introduction of S. rossanae n. sp. (see below), the occurrence of S. cavernicola and/or S. rossanae n. sp. in submarine caves from the Medes Islands ( Zabala 1986), and in shallow bathyal bottoms (250–750 m depth) from the Sicily Strait ( Harmelin 1979) remains to be ascertained.

Ecology. Setosella cavernicola is typical of submarine caves where it has been found in small cavities of organogenic concretions collected along walls and ceilings (6–40 m depth), in dark recesses and in transitional areas between semi-dark and dark sectors. Its occurrence in shallow bathyal bottoms must be checked, also in order to maintain the species within the ecological contingent of taxa typical of submarine caves and deep-water habitats (group 3 of Rosso et al. 2013b). Harmelin (2000) stated that colonies of S. cavernicola are obligate spots, each consisting of less than 10 zooids, but several colonies in the Plemmirio and Lesvos caves are comparably large.

Figures

FIGURE 8. a, b. Setosella cavernicola Harmelin, 1977. Holotype MNHN_IB_2008-13068. Trémies submarine cave near Cassis, Marseille, Lion Gulf. a. General view of the colony. b. Close-up of an autozooid. c, d. Setosella rossanae n. sp. MNHN_IB_ 2013-998 Trémies submarine cave near Cassis, Marseille, Lion Gulf, originally labelled as Setosella cavernicola and stored as a syntype at MNHN. c. General view of the colony. d. Close-up of an autozooid. Scale bars: a, c = 500 μm; b, d = 100 μm.

FIGURE 9. Setosella cavernicola Harmelin, 1977 PMC. B26. 30.6.2018a, Granchi cave, Plemmirio MPA, SE Sicily, W Ionian Sea, sample GR1P. a. General aspect of the colony after bleaching, showing no evidence of spiral growth. b. Cluster of zooids with a single pair of large opesiules and distal vibracula coaxial with the associated autozooid. c. Periancestrular area of the colony before bleaching. d. Two ovicellate autozooids, one still missing the associate distal vibraculum. Scale bars: a = 500 μm; b, c = 200 μm; d = 100 μm.

FIGURE 10. Setosella cavernicola Harmelin, 1977. PMC. B26. 30.6.2018b, Granchi cave, Plemmirio MPA, SE Sicily, W Ionian Sea, sample GR1P. a. View of a large, irregularly lobate colony. b. Periancestrular area with some autozooids showing an incompletely calcified cryptocyst. c. The bottom-right lobe in (a), developing from regeneration of some broken autozooids. d. Close-up of the regeneration line with irregular budding of autozooids and a kenozooid. e. Regenerated colony portion with the central fertile autozooid showing three subsequent intramural buddings. f. Anomalous budding of twin vibracula from a peripheral autozooid. g. Kenozooid (centre top) with a central, large, irregularly-shaped opesia. Scale bars: a, c = 500 μm; b, d–g = 200 μm.

FIGURE 11. Setosella cavernicola Harmelin, 1977. PMC. B26. 30.6.2018c, Fara cave, Lesvos Island, 11–18 m depth, NE Aegean Sea, sampling station FC2. a. Large lobate colony exploiting the extremely uneven surface of concretion cavities. b. Close-up of the central part in (a) with some autozooids, one regenerated as a kenozooid. c. Autozooids from a dead colony portion. d. Cluster of fertile autozooids. e. Ancestrula with associated vibracula located distally and on the lateral left side. Scale bars: a = 1 mm; b, d, e = 200 μm; c = 100 μm.

FIGURE 12. Setosella cavernicola Harmelin, 1977. PMC. B26. 30.6.2018c, Fara cave, Lesvos Island, 11–18 m depth, NE Aegean Sea, sampling station F4. a. Portion of a large, dead colony. b. Detail of an autozooid with the distal vibraculum and two large, disto-lateral opesiules. c. Cluster of autozooids with intramural budding. d. Close-up of the bottom-right colony portion in (a) Note the common regenerations in both autozooids and vibracula, some with closure plates. Scale bars: a = 500 μm; b = 100 μm; c, d = 200 μm.