Tennysonia stellata Busk, 1867

Taylor, Paul D., Waeschenbach, Andrea & Florence, Wayne K., 2011, Phylogenetic position and systematics of the bryozoan Tennysonia: further evidence for convergence and plasticity in skeletal morphology among cyclostome bryozoans, Zootaxa 3010, pp. 58-68 : 61-65

Tennysonia stellata Busk, 1867

( Figs 1–4 )

Tennysonia stellata Busk, 1867: 242 , pl. 36, figs 10, 11; Busk 1875: 34, pl. 31, fig. 6.

Material examined. NHMUK 75.5.29.63, fragment mounted on slide, Natal, Col. Bolten; this is a part of the specimen constituting the lower two of three drawings of Busk (1875, pl. 31, fig. 6), although the drawing is a mirror image of the original. NHMUK 99.7.1.5604, fragment mounted on slide, Natal, Colonel Bolten, Busk Collection (British Museum Catalogue). NHMUK 99.7.1.518, fragment mounted on slide, Natal, Col. Bolten, Busk Collection. NHMUK 99.5.1.1374, fragment mounted on slide, Port Elizabeth, Hincks Collection. NHMUK 99.5.1.1452, fragment mounted on slide, Port Phillip H. [presumably Port Phillip Heads, Australia, and mislabelled], Hincks Collection. NHMUK 34.10.20.4, fragment mounted on slide, Port Elizabeth, Vine Collection. NHMUK 1963.3.30.106, three fragments mounted on slide, Port Elizabeth, A.W. Thompson ex Jelly Collection. NHMUK 72.7.12.1, S.E. Cape Colony, Burrows Collection. NHMUK 72.7.30.12, two colonies, Port Natal, Burrows Collection. NHMUK 88.1.1.2, two colonies, Port Elizabeth, Burrows Collection. NHMUK 1968.1.16.107, shelly beach, East London, University of Cape Town Ecological Survey, 6 July 1937. NHMUK 72.8.6.5, three colonies, Natal. 72.8.6.5, three colonies, Natal, Colonel Bolden. NHMUK 2003.10.27.7, several branch fragments, registered together with another cyclostome species, Groot Bank, Plettenberg Bay, South Africa, 34°00.46’ S, 23°29.79’ E, 30 metres, 23 March 2000, Coral Reef Research Foundation. NHMUK 2003.10.27.13, Groot Bank, Plettenberg Bay, South Africa, 34°00.46’ S, 23°29.79’ E, 16 metres, 22 March 2000, Coral Reef Research Foundation. SAM A28765 , two branched fragments of narrow colony, RIY Bank, Port Elizabeth, South Africa, 33°58.15’ S, 25°52.01’ E, 23 metres, 18 October 2009, Iziko Museums Bryozoan Collection. SAM A28766 , one broad colony, RIY Bank, Port Elizabeth, South Africa, 33°58.15’ S, 25°52.01’ E, 23 metres, 18 October 2009, Iziko Museums Bryozoan Collection.

Distribution. Previously recorded from Cape Town (i.e. Cape of Good Hope), Plettenberg Bay, Port Elizabeth, East London and extending eastwards into Kwazulu Natal.

Description. Colony erect, ramifying, comprising branches of rounded subtriangular cross-section. Branch bifurcation angle approximately 45–90°, torsion of branches between bifurcations varying from minor, resulting in almost planar colonies, to moderate, resulting in more three-dimensional colonies. Anastomoses frequently in planar colonies, present but less common in three-dimensional colonies. Branches typically reflexed, the dorsal side concave in profile, varying in width from about 1.3 to 2.7 mm, delayed separation of branches after division of frontal midlines sometimes producing broader, flabellate sheets. Zooids opening on the two frontolateral branch surfaces; apertures of autozooids usually connate, arranged in transverse series of 5–9 autozooids per series, those on opposite frontolateral sides alternating along crest at branch midline, diameter typically showing a slight gradient of increase towards branch midline; spacing between connate series a little greater than autozooidal aperture diameter, occupied by kenozooids. Branch dorsal (reverse) surface formed of pseudoporous exterior wall, slightly convex, smooth apart from arcuate growth bands, traces of interzooidal walls visible through exterior wall under an optical microscope, defining long, narrow proximal parts of newly budded zooids. Overgrowths irregularly developed on branch dorsal surfaces, particularly in basal parts of colonies, comprising kenozooids either with or without calcified exterior walls. Transversely fractured branches reveal small, new buds only along exterior wall of dorsal branch surface. Ancestrula and early astogeny unknown, proximal parts of all available colonies either broken-off or obscured by kenozooidal overgrowths.

Autozooids free-walled or fixed-walled. Apertures polygonal in free-walled autozooids, 0.15–0.27 mm in diameter, subcircular to longitudinally elliptical in fixed-walled autozooids, 0.13–0.17 mm in diameter. Peristomes absent in free-walled autozooids, very short and collar-like in fixed-walled autozooids. Apertural spines comprising thickened, pustulose patches of interior wall around rims of some autozooidal apertures, commoner at wall triple junctions. Exterior-wall calcification closing some autozooidal apertures, particularly to dorsal surface of Kenozooids smaller and more irregularly polygonal in shape than autozooids, either free-walled throughout colony or becoming fixed-walled a variable distance proximally of branch growing tips, generally arranged in 1–3 ill-defined rows between autozooidal apertures.

Gonozooids infrequent (only two examples observed), opening frontally, brood chamber ovoidal in outline, extending across both frontolateral branch surfaces, incorporating 2–3 series of autozooids, some of which protrude through roof as single, pairs or triplets of apertures. Roof formed of exterior wall with denser and larger pseudopores than elsewhere. Ooeciopore not identified, either destroyed by breakage of roof or indistinguishable from autozooidal apertures.

Interior walls with fabric of transverse fibres near wall growing edges. Interzooidal pores numerous, partly closed by numerous centripetal spines extending into pore lumens, <10 µm in diameter. Pseudopores subcircular, some with iris-like partial closure formed by a small number of basally coalesced centripetal spines, <10 µm in diameter.

Remarks. This species was said by Busk to have a pale rose tint and be parasitic on Onchopora tubulosa , although our fresh material from Port Elizabeth is yellow in colour. The material described by Busk came from the Cape of Good Hope and was supplied by ‘Dr. Rubidge (Mrs. Gatty)’. Busk (1867) regarded the species to be most closely related to Discoporella Gray and assigned it provisionally to the family Diastoporidae Busk, 1859 . However, in 1875 he transferred it ‘doubtfully’ to his new family Discoporellidae, adding that it ‘should probably be regarded as a Heteropora’ [ Heteropora Blainville, 1830 is a genus nowadays assigned to the suborder Cerioporina , see Nye 1975]. Notably, Busk (1875) described Diastoporidae as having ‘no cancelli’ but Discoporellidae as having a ‘cancellated or porous’ surface.

Curiously, Busk’s text (1867, p. 242) failed to associate a species name with his new genus Tennysonia , although the trivial name stellata is specified in the plate description.

None of the NHMUK specimens correspond with the colonies depicted by Busk (1867) or match the locality (Cape of Good Hope) or habitat and collection details stated by Busk (1867, p. 242): ‘parasitic upon Onchopora tubulosa . Dr. Rubidge (Mrs. Gatty)’. The whereabouts of Busk’s syntypes, if they still exist, are therefore unknown.

Figures

FIGURE 1. Tennysonia stellata Busk, 1867, photographs of fragments of bleached colonies. A, colony with relatively narrow, bifurcating and anastomosing branches, NHMUK 72.8. 6.5, Natal; B, fragment of specimen figured by Busk (1875, pl. 31, fig. 6), NHMUK 75.5. 29.63, Natal; C, flabellate colony morphotype with delayed separation of bifurcating branches, NHMUK 2003.10. 27.13, Groot Bank, Plettenberg Bay. Scale bars: A, C: 5 mm; B: 1 mm.

FIGURE 2. Tennysonia stellata Busk, 1867, scanning electron micrographs of distal branches showing variations in skeletal organization. A, branch comprising entirely free-walled zooids, SAM A 28766, RIY Banks, Port Elizabeth; B, branch with freewalled organization distally but becoming fixed-walled at level of arrow by development of calcified exterior over the kenozooidal apertures, SAM A 28765, RIY Bank, Port Elizabeth; C, branch comprising entirely fixed-walled zooids, NHMUK 2003.10. 27.7, Groot Bank, Plettenberg Bay. Scale bars: A, B: 1 mm; C: 500 µm.

FIGURE 3. Tennysonia stellata Busk, 1867, scanning electron micrographs showing skeletal morphology. A – C, SAM A 28766, RIY Bank, Port Elizabeth. A, transverse series of autozooidal apertures separated by smaller kenozooidal apertures on left frontolateral branch surface with exterior wall of branch dorsal surface visible in lower left; B, detail of apertures showing spines; C, spine developed at triple junction between three interzooidal walls which have an ultrastructural fabric of transverse fibres (right). D, E, SAM A 28765, RIY Bank, Port Elizabeth. D, transition from free-walled (left) to fixed-walled organization (right); E, enlargement showing sheet-like exterior wall (arrowed) covering kenozooidal apertures. F, NHMUK 2003.10. 27.7, Groot Bank, Plettenberg Bay, rows of autozooidal apertures separated by exterior wall calcification in fixed-walled branch. G, H, NHMUK 2003.10. 27.13, Groot Bank, Plettenberg Bay. G, development of exterior wall calcification, at varying levels relative to vertical interzooidal walls, over kenozooids and most of the autozooids (apart from 5 apertures which remain open); H, lobes of exterior wall calcification extending between autozooidal series. I – L. NHMUK 34.10. 20.4, Port Elizabeth. I, apertures closed by exterior wall calcification, one occluded autozooid having a small central dimple; note apertural spines standing up above level of exterior walls (top right); J, gonozooid with broken brood chamber roof; K, lobate brood chamber roof (left) with denser pseudopores than exterior walls covering kenozooids (lower right); L, detail of pseudopores from brood chamber roof, some partly closed by spines. Scale bars: A, D, G, H: 500 µm; B, E: 100 µm; C, L: 20 µm; F, I, K: 200 µm; J: 1 mm.

FIGURE 4. Tennysonia stellata Busk, 1867, colony morphotypes with A, narrow branches, (SAM A 28765) and B, broad branches (SAM A 28766). RIY Bank, Port Elizabeth. Scale bars 10 mm.