Adelascopora secunda Hayward and Thorpe

Hayward, Peter J. & Winston, Judith E., 2011, Bryozoa collected by the United States Antarctic Research Program: new taxa and new records, Journal of Natural History 45 (37 - 38), pp. 2259-2338 : 2316-2319

Adelascopora secunda Hayward and Thorpe

( Figures 27 , 28 ; Table 1)

Adelascopora secunda Hayward and Thorpe 1988c: 293 , figs 5E, F; Hayward 1995: 301, fig. 175E.

Adelascopora jeqolqa Moyano 1989: 164 , figs 2, 4, 5, 7–9, pl. 1(Ad, Md, Dd), pl. 2(Ad, Md); Hayward 1995: 300, fig. 175C,D.

Pseudoadelascopora weddellae Gontar, 2002: 291 , figs 3, 6.

Material

Eltanin cruise 9, station 740, 56 ◦ 06’ to 56 ◦ 07’ S, 66 ◦ 19’ to 66 ◦ 30’ W, 494– 384 m, 18 September 1963; numerous (> 50) fragments of erect cellariiform and flustriform colonies, 34 with bipartite, nodulated chitinous stems; 13 pieces of substratum (gravel, shell and an echinoderm spine) bearing unilaminar encrusting sheets, giving rise to erect, cellariiform and flustriform shoots.

Remarks

Adelascopora was introduced by Hayward and Thorpe (1988c) for two species of Microporellidae : Microporella divaricata Canu, 1904 and Adelascopora secunda sp. nov. Microporella divaricata had been described from Tertiary fossil deposits of Patagaonia ( Canu 1904), described and illustrated by Waters (1904) from extant material collected in the Bellingshausen Sea, and subsequently reported from other Antarctic localities ( Livingstone 1928; Androsova 1972). The new genus was especially characterized by its erect, branching habit, lack of spines and avicularia, and by its ovicell, the ectooecium of which is entirely membranous. The type species, Adelascopora divaricata develops a slender, branching cellariiform colony, with dichotomies marked by tubular, chitinous nodes, while A. secunda grows as flabellate, bilaminar fronds. Moyano (1989) described and illustrated substantial material of both taxa from several localities in the South Shetland Isles and the Antarctic Peninsula, demonstrated that all Recent records of “ A. divaricata ” represented a species distinct from the Patagonian fossil, and assigned them to the new taxon, A. jeqolqa . The two species display very similar autozooid morphology, and dimensions of the autozooids and orifice overlap between them; however, colony form was seen to be fundamentally different and both taxa were upheld by Hayward (1995).

The sample from Eltanin cruise 9, station 740 provides interesting new data on the morphology of Adelascopora and demonstrates that only a single species may be recognized. The erect fragments represented both cellariiform and flustriform colonies, and many of the former displayed the chitinous nodes described by Moyano (1989). The broadest flustriform fragment had nine series of autozooids per row, on each face of the frond, and one on each edge. The cellariiform fragments with rootlets all had a basal whorl of five autozooids; in some this number remained constant for four to six astogenetic generations, in others it increased to double that number in the same number of generations. Some shoots appear nodulated as a consequence of broad autozooids being succeeded by much narrower autozooids at the division of autozooid series, but no growth checks were apparent in the calcification. Eleven small pieces of gravel, a small bivalve shell and a portion of an echinoderm spine, were encrusted with contiguous, unilaminar sheets of autozooids ( Figure 27A ), among which were modified zooids, lacking orifices ( Figure 28B ), but with bipartite, annulated chitinous tubes issuing from their frontal surfaces ( Figure 27B,D ), from which erect colonies of Adelascopora were growing. These included both narrow, cellariiform and broad, flustriform growths. The encrusting colonies occupied from 10 to 100% of the surface area of the substratum, and bore from one to 14 erect shoots ( Table 1).

The Pseudoadelascopora weddellae described and figured by Gontar (2002) was founded on two flabellate, bilaminar colonies and one cellariiform colony, all with variously developed chitinous nodes. The autozooid morphology appears to be identical to that described here for A. secunda . The “endozooecial ovicells” described by Gontar (2002), and considered to be diagnostic of the new genus, Pseudoadelascopora , actually represent the calcified basal walls of hyperstomial ovicells, as shown in previous SEM figures ( Hayward 1995, fig 17C).

Notes: Measurements in mm; range (mean ± SD) for shoot lengths.

∗ Substratum 11 is a bivalve shell, substratum 12 is an echinoid spine, the rest are gravel. The colony of A. secunda therefore displays biphasic morphology; the founding ancestrula grows as a unilaminar encrusting sheet, which then produces erect shoots which may be broad or narrow, and jointed or not. It might be speculated that this growth form is an ecophenotypic expression, in response to limited or small and unstable substrata, and that under other microenvironmental conditions the colony might simply develop as an encrusting sheet. Intriguingly, without evidence of erect growth, or its ovicell, such a colony would be recognized by most bryozoan specialists as a species of Fenestrulina , and it might be further speculated that some poorly characterized, southern ocean species of “ Fenestrulina ” might in fact represent the encrusting phase of perhaps undescribed species of Adelascopora . In defining such taxa it is essential to consider that a sample of erect “colonies” from a single sampling point might represent the ramets of a single genet, and that observed variation within the sample might reflect intracolony variation.

Figures

Figure 27. Adelascopora secunda. (A) A unilaminar colony encrusting a piece of gravel, with four erect shoots; (B) base of a shoot, arising from a single chitinous tube; (C) distal portion of an erect, cellariiform shoot, showing abrupt broadening; (D) basal portion of an erect shoot, with bipartite chitinous tube. Scale bars: 0.5 mm.

Figure 28. Adelascopora secunda. (A) Autozooids from an erect cellariiform shoot; (B) part of the encrusting portion of the colony, with two kenozooids from which originated the bipartite chitinous base of an erect shoot. Scale bars: 0.25 mm.