Olisthella plana, Gordon, Dennis P. & Taylor, Paul D., 2017

Gordon, Dennis P. & Taylor, Paul D., 2017, Resolving the status of Pyriporoides and Daisyella (Bryozoa: Cheilostomata), with the systematics of some additional taxa of Calloporoidea having an ooecial heterozooid, Zootaxa 4242 (2), pp. 201-232 : 218-219

Olisthella plana n. sp.

( Fig. 8 A)

Material examined. Holotype: NIWA 95617 , NIC Wellington, Stn TAN 0413 /8, 36.8370° S, 177.4647° E 1319– 1486 m, Whakatane Seamount, southern Havre Trough , 8 November 2004 . Paratype: NIWA 22519 , NIC Wellington, Stn T 239, 30.1367° S, 178.5383° W, 905 m, NW of Macauley Island, Kermadec Ridge , 23 March 1982 . Other material: NIWA 23168 , NIC Wellington, same data as for holotype.

Etymology. Latin planus, level, flat, alluding to the flat cryptocystal shelf.

Description. Colony unilaminar, multiserial, comprising fully contiguous autozooids in quincunx; maximum spread 3.6 mm, hence small and spot-like. Autozooids more or less elongate-oval or of more irregular outline [ZL 610–945 (796); ZW 489–689 (582)]. Gymnocyst very little developed, mostly visible proximally and proximolaterally. Cryptocyst and opesia encircled by a raised granular rim that is nearly evenly circular or oval except where it is indented by oral-spine bases [CrL 478–700 (581); CrW 433–578 (506)]. Cryptocystal shelf moderately broad and flat, of nearly equal width proximally and laterally, curving inward just proximal of the spine bases and continuing as a narrow extension on each side to be level with the distal oral rim; surface evenly granular except for a conspicuous smooth band around the margin of the opesia. Opesia about twice as long as wide, a little constricted near the level of the proximalmost oral spines, but lacking actual condyles [OpL 221–389 (311)]. Opercular flap occupying entire area of opesia distal to indentations. Articulated oral spines only, three on each side, none mid-distally; no other opesial spines; 0–2 additional very tiny spines borne on gymnocyst, one either side of the proximalmost spine base. No avicularia. Ooecium hyperstomial, smooth-surfaced, with a longitudinally elongate excavation in the ectooecium bordered by a low, raised rim [OoL 300–322 (311); OoW 256–289 (281)]. Ooecial kenozooid extremely well developed, projecting well beyond the ooecium distally, having a small opesial foramen and extensive sunken, flat granular cryptocyst bounded by a lateral gymnocyst, and a tiny single adventitious spine borne mid-distally. Interzooidal kenozooids rare, more or less elongate-oval [KL 312]; intrazooidal kenozooids formed by regenerative budding within some autozooidal cystids, their surface superficially appearing as opesial closure plates; occupying only the area beneath the opesia, not the entire cystid (as seen from beneath); each with a small foramen surrounded by a granular area of cryptocyst. Ancestrula not seen.

Remarks. Of the species described above, O. plana n. sp. most resembles O. contigua n. sp., differing in several features, however, especially the lack of pericryptocystal spines and well-developed gymnocystal spines, as well as the coarse granularity of the cryptocyst and minimum development of the gymnocyst. The ooecium is lacking in O. contigua n. sp., so no comparison can be made in this regard. The ectooecial excavation and the exceptional development of the ooecial kenozooid in O. plana n. sp. stand out as highly diagnostic, inviting comparison with the genus Megapora Hincks, 1877 . Both of these characters are found in the type species from Europe, Megapora ringens ( Busk, 1856) (cf. Hayward & Ryland 1998, fig. 58B; Di Martino & Taylor 2012, figs 41, 42), although the ooecial kenozooid is rather smaller in M. ringens . Despite the similar reproductive features, M. ringens differs significantly from O. plana n. sp. in having a trifoliate opesia and a cryptocystal ridge that is within the cryptocyst, not separating it from the gymnocyst.

It was initially thought that O. plana n. sp. might represent a new genus; inter alia, whereas the ooecial kenozooid is wholly concealed from frontal view in O. occlusa n. sp. and O. alma n. sp., in O. plana it is exceptionally well developed, projects distad from the ooecium and has a frontal foramen, cryptocyst and spine. Additional discriminating characters include horizontal lateral extensions of the cryptocystal shelf as far as the distal zooidal rim and a discrete smooth band of calcification bordering the opesia. Ooecia are so far unknown in the congeners O. contigua n. sp. and O. mimica n. sp.; when discovered they will no doubt shed further light on relationships within the genus. In the cladistic analysis presented here ( Fig. 15 ), Olisthella n. gen. would be rendered paraphyletic if O. plana n. sp. were segregated as a new genus.

Distribution. Endemic to the New Zealand EEZ, where it is known only from the central and southern Havre Trough at 905–1486 m depth, encrusting small volcanic clasts.

Figures

FIGURE 8. Olisthella plana n. gen., n. sp., holotype, NIWA 95617: A, part of colony with autozooids and ovicellate zooid (arrows indicate tiny spine-bases on lateral gymnocysts); note the distal exposure of the ooecial kenozooid, with an extensive cryptocystal area. Pyriporoides murdochi n. sp. B – D, holotype, NIWA 136; E, unregistered: B, ovicellate zooid (note the spined ooecial kenozooid and the paired distal spines on the lateral gymnocyst of the maternal zooid); C, autozooids, showing short caudae; D, disposition of autozooidal spines; E, ancestrula. Scalebars: A, 500 µm. B – D, 200 µm; E, 100 µm.

FIGURE 15. Phylogenetic tree of hypothesised relationships between extant species of the taxa described and redescribed herein plus outgroup taxa. As described in the text, this is the single minimum length tree generated by a heuristic search using PAUP with character reweighting. The two outgroup taxa used to root the tree were Amphiblestrum trifolium and Pyrisinella meniscacantha. The matrix used to compute the tree can be found in Appendix 1, and the characters and their states are given in Appendix 2. Character changes (states are in parenthesis) along lettered branches are as follows: A, character 15 (0 Ą 1), 16 (0 Ą 1), 19 (1 Ą 0); B, 7 (0 Ą 2), 14 (0 Ą 1), 22 (1 Ą 0); C, 3 (0 Ą 2), 11 (0 Ą 1); D, 6 (1 Ą 0), 8 (4 Ą 0), 12 (0 Ą 1), 13 (0 Ą 1); E, 1 (2 Ą 0), 2 (0 Ą 2), 14 (1 Ą 0); F, 10 (0 Ą 3), 16 (1 Ą 2); G, 2 (2 Ą 1), 8 (0 Ą 1); H, 19 (0 Ą 1), 22 (0 Ą 1); I, 18 (0 Ą 1); J, 4 (1 Ą 0), 13 (1 Ą 0); K, 18 (0 Ą 1); L, 5 (0 Ą 1), 8 (0 Ą 1), 17 (0 Ą 1); M, 18 (0 Ą 1); N, 10 (0 Ą 1); 14 (0 Ą 1); O, 13 (1 Ą 0); P, 2 (2 Ą 0 / 1); Q, 7 (2 Ą 0), 10 (0 Ą 2), 23 (1 Ą 0); R, 1 (2 Ą 1), 4 (1 Ą 1), 6 (0 Ą 1), 7 (0 Ą 1), 8 (0 Ą 3); S, 5 (0 Ą 1); T, 10 (2 Ą 3); U, 8 (0 Ą 1), 22 (0 Ą 1); V, 4 (1 Ą 0), 18 (0 Ą 1); W, 8 (1 Ą 2), 12 (1 Ą 0), 13 (1 Ą 0), 17 (0 Ą 1); X, 9 (0 Ą 1), 18 (0 Ą 1).