Disporella guada Harmelin, Taylor & Waeschenbach, 2021

Taylor, Paul D., Harmelin, Jean-Georges, Waeschenbach, Andrea & Bouchon, Claude, 2021, Disporella guada sp. nov., an erect-ramose rectangulate cyclostome (Bryozoa, Stenolaemata) from the Caribbean Sea: convergent evolution in bryozoan colony morphology, European Journal of Taxonomy 773, pp. 1-18 : 4-12

publication ID	https://doi.org/ 10.5852/ejt.2021.773.1507
publication LSID	lsid:zoobank.org:pub:51990779-969E-412C-B6F5-5E01A8103410
DOI	https://doi.org/10.5281/zenodo.5560013
persistent identifier	https://treatment.plazi.org/id/E6E2D7BF-A429-4ABE-B91F-4D33DE70D033
taxon LSID	lsid:zoobank.org:act:E6E2D7BF-A429-4ABE-B91F-4D33DE70D033
treatment provided by	Felipe
scientific name	Disporella guada Harmelin, Taylor & Waeschenbach
status	sp. nov.

Treatment

Disporella guada Harmelin, Taylor & Waeschenbach sp. nov.

urn:lsid:zoobank.org:act:E6E2D7BF-A429-4ABE-B91F-4D33DE70D033

Figs 1–5 View Fig View Fig View Fig View Fig View Fig

Differential diagnosis

Disporella with erect, ramose colonies up to at least 30 mm in width and height; branches short and thick; branch axes constituting an endozone formed by proximal parts of zooids oriented parallel to branch axis, surrounded by an exozone formed by the distal parts of these zooids bent to become oriented at right angles to the axis; maculae circular to elongate in outline, comprising kenozooids. Autozooids with multiple apertural spines, the aperture often closed by a calcified diaphragm containing a central lumen. Gonozooid irregularly ramifying, the interior-walled roof rapidly concealed by a honeycomb of secondary calcification; ooeciopores at distal ends of lobes, occasionally paired, rounded quadrangular, without an ooeciostome.

Etymology

From Guadeloupe, the type locality.

Material examined

Holotype FRENCH WEST INDIES, GUADELOUPE • the largest collected spec. ( Figs 1A View Fig , 2A View Fig ) (kept dry, Hc 28 mm, Wc 38 mm, Bd 5.4–6.2 mm, Db 2.3–3.6 mm, Hp 320–500 µm, Nt 26, + 3 broken tips, coated for SEM); Islet “Tête-à-l’Anglais”; 16°22.936′ N, 061°45.925′ W; 5 m depth; 10 Oct. 2014; CB leg.; MNHN-IB-2017-696 . GoogleMaps

Paratypes FRENCH WEST INDIES, GUADELOUPE • 1 spec. (paratype A: Hc 20 mm, Wc 2.4 mm, Nt 8; preserved in ethanol); Islet “Tête-à-l’Anglais”; 16°22.916′ N, 061°35.140′ W; 3–5 m depth; 7 Nov. 2016; CB leg.; MNHN-IB-2017-697 GoogleMaps • 1 spec. (paratype B: Hc 20 mm, Wc 16 mm, Nt 5; preserved in ethanol); same collection data as for preceding; CB leg; MNHN-IB-2017-698 ( NHMUK 2018.1.15.63 hologenophore) GoogleMaps • 7 specs; same collection data as for preceding; NHMUK 2021.2.25.1 , NHMUK 2021.3.19.1 , NHMUK 2012.3.19.2 , NHMUK 2021.6.14.1 , NHMUK 2021.6.14.2 , NHMUK 2021.6.14.3 , NHMUK 2021.6.14.4 GoogleMaps .

Other material

FRENCH WEST INDIES, GUADELOUPE • 11 colonies, small to medium-sized (Hc 8-15 mm) with varied shape (small: columnar, larger: ramified), preserved in ethanol; same collection data as for paratype A; MNHN-IB-2017-699–709 GoogleMaps .

Morphology

Colony white when alive ( Fig. 1A–B View Fig ), heavily calcified, erect, up to 30 mm in both height and width in collected material, rapidly and irregularly ramified in all directions from a short basal trunk, branches short and thick but variably sized, roughly cylindrical or slightly flattened, with rounded tips ( Fig. 2B– C View Fig ); the largest colony (holotype) with 29 branch tips ( Fig. 2A View Fig ). Distal branch growing tips hemispherical, exposing a mixture of autozooidal and kenozooidal apertures ( Fig. 2D View Fig ); interzooecial walls with a broken medial ridge; spines lacking ( Fig. 2E View Fig ). Marginal lamina apparently absent at the base of colonies (juvenile specimens not seen). During growth, the base of the colony ( Fig. 2 View Fig C-a) can increase the diameter of its attachment surface by the downward budding of a peripheral blade apparently made of kenozooids ( Fig. 2 View Fig C-b).

Surface of branches occupied by autozooids and kenozooids ( Figs 3B, D–E View Fig , 4A View Fig ). Transverse section of branches revealing an axial endozone occupying 40–50% of the area ( Fig. 3C View Fig ), formed by proximal parts of zooids growing parallel to branch axis, surrounded by an outer exozone corresponding to the distal parts of these zooids bent at right angles to the branch axis ( Fig. 2C View Fig ). Lateral walls of zooids very thick, moniliform, with pointed mural spines or pustules ( Fig. 4D–E, H View Fig ) and communication pores hourglass-shaped in vertical section ( Fig. 4G View Fig ), originating at the surface of the colony (see below). Skeletal ultrastructure granular in appearance at growing edges, lacking a layer of transverse fibres.

Kenozooids with rounded apertures ( Fig. 4A View Fig ) smaller than those of the autozooids (25–45 µm), occasionally associated (frequently in the largest specimen) with a single pointed process rising vertically or slightly bent ( Fig. 4C View Fig ), scattered between autozooids or clustered together to form maculae on the colony surface ( Fig. 3B View Fig ). Maculae of variable shapes and sizes, from relatively small and nearly circular to large and elongated along branches ( Fig. 3A View Fig ), particularly frequent near branch bifurcations.

Autozooids loosely arranged in quincunx or more irregularly, interspersed with kenozooids. Peristomes short, the largest (up to 500 µm) in the shape of a concave blade arising from the distal edge of the aperture, tip truncated (gouge-shaped) or pointed, with a large oblique opening reaching the colony surface; a pair of pointed processes lateral to the blade on medium-sized peristomes ( Fig. 3E View Fig ), the smallest peristomes reduced to a short, arched wall with up to 4 or 5 terminal pointed processes ( Fig. 3D View Fig ). Communication pores visible below the outer rim of apertures of both kenozooids and autozooids, and also in the peristomes of autozooids ( Fig. 4E View Fig ).

Mural spines pointed and variously sized, or short and blunt (pustules), abundant inside tubes of autozooids and kenozooids (up to 15–18 around the circumference of kenozooidal apertures) ( Fig. 4A, E–H View Fig ), and on the outer sides of brood chambers with fewer on the inner sides.

Calcified diaphragms present in kenozooids and in some autozooids of large (presumably old) specimens ( Fig. 4B–C View Fig ), subterminal, funnel-shaped, iris-like with a central lumen of varying size (8–25 µm), adorally curved at contact with the interzooecial walls, a clear discontinuity visible between the outer edge of the diaphragm and these walls ( Fig. 4F View Fig ); a succession of diaphragms spaced 100 to>500 µm apart seen in sectioned zooids, suggesting sequential growth and resting stages.

Brood chambers irregularly ramose with narrow lateral branches ( Fig. 5A View Fig ), sub-circular in section ( Fig.5C View Fig ), interior-walled, floor and roof formed by a thin skeletal layer, roof rapidly concealed by secondary calcification starting with a honeycomb mesh structure ( Fig. 5A–B View Fig ); outer surface of overgrowths densely dotted with large pores soon closed by a calcified diaphragm inserted below the surface, inner surface smooth or with small pustules. Ooeciopore at distal end of lobes, occasionally paired (i.e., two ooeciopores are present in the same lobe) ( Fig. 5D View Fig ), widely open, more or less quadrangular with rounded corners, the upper edge corresponding to the boundary of the brood chamber; ooeciostome lacking.

Remarks

This new species of Disporella is distinguished from all others in the genus by its erect colony-form with bifurcating branches. It was initially believed to be a species of Doliocoitis Buge & Tillier, 1977 , regarded as a cerioporine by these authors but which has an interior-walled gonozooid as noted by Gordon & Taylor (2001) and is therefore a rectangulate. The type species of this genus, Doliocoitis atlantica Buge & Tillier, 1977 from the Gulf of Guinea, has a semi-erect colony with claviform branches that do not bifurcate, whereas a second species, Doliocoitis cyanea Gordon & Taylor, 2001 from New Zealand, has encrusting colonies. A morphological comparison between Disporella guada sp. nov., Doliocoitis atlantica and Doliocoitis cyanea is presented in Table 1. A View Table 1 key difference between Disporella guada sp. nov. and the two species of Doliocoitis is the erect bifurcating colony-form of Disporella guada sp. nov., the branches comprising an axial endozone surrounded by an exozone. However, the structure of the basal part of the sectioned colony of D. guada sp. nov. ( Fig. 2C View Fig ), with secondary downward growth of a peripheral blade, matches with the process of basal thickening in Doliocoitis atlantica described and figured by Buge & Tillier (1977: 6, fig. 2). Doliocoitis lacks the prominent interior-walled peristomial spines that characterize Disporella guada sp. nov., although the apertural rims in Doliocoitis cyanea do have short processes on one side.

Habitat and colony shape

Disporella guada sp. nov. was found at two sites in the French West Indies characterised by the same general environmental conditions, i.e., very shallow depth (3–5 m) and exposure to strong wave action. Variously sized colonies of D. guada sp. nov. grow on the shadowed side of rocks together with sponges, hydroids, gorgonians, and the stylasterid Stylaster roseus (Pallas, 1766) , but apparently without large macrophytes. The highly robust colonies of this erect species, owing to small size and very thick trunk and branches, seem well adapted to life in a high-energy flow regime. In the largest and most profusely ramified colony collected (the holotype), the ratio of colony height (28 mm) to mean branch width (3.5 mm) is particularly low (8). This ratio contrasts with the very high values seen, for example, in large colonies of branched cheilostomes inhabiting conditions of reduced flow, such as in caves. The finding of D. guada sp. nov. only in high flow regimes where colonies are stocky raises the question of whether it is specialized for this particular habitat. Many species of cyclostomes exhibit considerable plasticity in colony form according to the microenvironment inhabited ( Harmelin 1975, 1976). Therefore, it cannot be ruled out that D. guada sp. nov. is present also in other unexplored microhabitats – such as the undersides of boulders, in cavities or in deeper water – where the shape of the colonies may be different.

Molecular phylogeny

Previous studies on cyclostome phylogenetics have revealed several unexpected results ( Waeschenbach et al. 2009; Taylor et al. 2011, 2015; Taylor & Waeschenbach 2019), which is why the newly generated data were analysed in the broader context of cyclostome phylogeny ( Fig. 6 View Fig ). Bayesian inference places D. guada sp. nov. firmly in the genus Disporella (Rectangulata) , in a strongly supported clade that also includes Plagioecia patina (Tubuliporina) and sister taxa Doliocoitis cyanea (Rectangulata) and Favosipora rosea Gordon & Taylor, 2001 (Cerioporina) . The remainder of the phylogeny largely corresponds to previous versions, except reduced nodal support (0.89 pp) for a sister-group relationship of Crisia spp. and the remainder of Clade C in Waeschenbach et al. (2009), and a switch in positions between Annectocyma tubulosa (Busk, 1875) and Heteropora sp. 1 compared to the topology presented by Taylor et al. (2015) and Taylor & Waeschenbach (2019).