Steginoporella discors, Gordon & Voje & Taylor, 2017

Gordon, Dennis P., Voje, Kjetil L. & Taylor, Paul D., 2017, Living and fossil Steginoporellidae (Bryozoa: Cheilostomata) from New Zealand, Zootaxa 4350 (2), pp. 345-362 : 353-355

Steginoporella discors n. sp.

( Figs 1D , 20 , 26–27 , 34 )

Steganoporella (Vincularia) neozelanica: Hincks 1882: 119 . Non Steginoporella neozelanica ( Busk, 1861) . Steganoporella neozelanica var. magnifica: Livingstone 1929: 66 , text-fig. 2c, pl. 1, fig. 11. Non Steginoporella magnifica Harmer, 1900 .

Steginoporella magnifica: Pouyet & David 1979b (part): 783; Gordon 1984 (part): 56, pl. 17B.

Etymology. Latin discors , different, disagreeing, alluding to differences from Steginoporella magnifica , which is superficially similar.

Material examined. Holotype: NIWA 122575, Stn E 842, 33.900° S, 172.283° E, near Bowling Bank, NE of Three Kings Islands , 16 March 1968, 187– 224 m. Paratypes: NIWA54409 , TAN0906 /2, 35.552° S, 174.560° E, ENE of Matapouri , Northland , 4 April 2009, 55 m; NIWA 122670, same data as for holotype ; NHMUK: 1967.2.8.127, Terra Nova Stn 144, c. 34.55° S, 172.54° E, SW of Cape Maria van Diemen , 13 September 1911, 64– 73 m.

Other: NIWA 122664, Stn Z9743; NIWA 122672, Stn Z8639; NIWA 122673, Stn KAH9901/29. Plus unregistered (non-separated) specimens in multispecies samples from NIWA Stations K795, K797, K820, K822, K824, K850, K851, K855, K857, Z8639, Z8662.

Description. Colony encrusting, unilaminar, forming inversely calyciform structure through overgrowth of other sessile organisms, or a long open cone to> 40 mm length. Colour in life pale brownish-beige.

Zooids monomorphic, broadly subpyriform with mostly tapering proximolateral margins, roundly truncate proximally, longer than wide (mean L/W = 1.31), widest at level of opercular pivots or just distal of these. Cryptocystal area smaller than opesia; shelf comprising two parts, a coarsely granular narrow area proximally and laterally, edged by acute tubercles, below which is very short area with occluded pseudopores that steeply descends to large proximomedial foramen. Distal edges of polypide tube extend into space beneath operculum like a scoop.

Opercular opening delimited by stout triangular pivots and thin edge of well-developed median process, with distolateral ‘wings’ that do not meet pivots or lateral margin; proximomedial foramen large, pocket-shaped. Inner face of operculum smooth, lacking reticular sclerites.

Polypide not seen. Ancestrula like that in S. magnifica , but two daughter zooids budded from one side, with additional zooids produced from them, long before any zooids are budded distally or from opposite side of ancestrula.

Measurements. In micrometres: ZL 1013±40, 940–1078 (1, 10); ZW 773±29, 733–812 (1, 10); OpL 396±29, 343–444 (1, 10); OpW 579±35, 510–612 (1, 10).

Remarks. Steginoporella discors n. sp. has been confused in the past with S. magnifica (e.g. by Gordon 1984, 1986). Both are coastal species that form large encrustations, but whereas colonies of S. magnifica form closely adherent crusts on firm substrata, those of S. discors n. sp. encrust less-consolidated hard substrata, draping the colony to follow the contours of the substratum and crossing gaps. The species apparently even encrusts reasonably firm sponges—the holotype colony was found in the NIWA collection, detached from any substratum, as a unilamellar crust. Further, the paratype colony is highly distinctive, having the form of a hollow waffle cone, with one opening larger than the other ( Fig. 1D ). It is not clear how the colony acquired its form but it is likely to have begun life encrusting a biogenic surface, perhaps a cylindrical sponge stem, which subsequently decayed. Hincks (1882) noted that an encrusting colony of ‘ Steganoporella (Vincularia) neozelanica ’ was spread over a sponge—it is near certain that he had S. discors n. sp.

Like all other coastal and shelf congeners in New Zealand, S. discors n. sp. has monomorphic zooids, but differs strikingly from them in its foreshortened steeply descending cryptocystal shelf and lack of reticulate opercular sclerites. Livingstone (1929) was puzzled by an encrusting form from 119 m at the Three Kings Islands that lacked reticular sclerites in the operculum; with some hesitation he ascribed it to ‘ Steganoporella neozelanica var. magnifica ’. It is clear from his illustrations of zooids and an operculum that he had S. discors n. sp. Likewise, Gordon (1984) illustrated nominal S. magnifica from the Kermadec Ridge; the foreshortened cryptocystal shelf and visible polypide tube show that this too belongs to S. discors n. sp.. Steginoporella magnifica is rare on the Kermadec Ridge, where it partly connects the distribution of the species between Tonga and the main islands of New Zealand.

Pouyet & David (1979b, p. 784) stated that S. magnifica occurred at 75° S latitude based on a specimen collected by the British Antarctic Expedition, but this record was misattributed; the cited specimen, presently registered as NHMUK1967.2.8.127, was collected by the Terra Nova off northern New Zealand. Our examination of this specimen shows it to be S. discors n. sp., not S. magnifica , and it is nominated as a paratype.

Distribution. Endemic to northern New Zealand: Kermadec Ridge, Three Kings Islands, Cape Maria van Diemen, NE coast of Northland; 55– 615 m.

Figures

FIGURE 1. Six species of Recent New Zealand Steginoporella (NIWA stations in parentheses). A, S. neozelanica (TAN 1105 / 27); B, S. marcusi (respectively from three localities, left to right, D 896, TAN 1105 / 42, TAN 1105 / 60); C, S. perplexa (small colony from Z 15617); D, S. discors n. sp. (TAN 0906); E, S. modesta n. sp. (TAN 0413 / 109); F, S. lineata n. sp. (TAN 0205 / 64). All to same scale (scalebar 25 mm).

FIGURES 20 – 25. Zooids of New Zealand Steginoporella (NIWA stations in parentheses). 20, S. discors n. sp. (Z 9743); 21, 23, S. modesta n. sp., respectively showing autozooids and an ancestrula and daughter zooid (TAN 0413 / 109); 22, 24 – 25, S. lineata n. sp., showing autozooids and larger avicularian B-zooids (TAN 0205 / 64). Figs 20 – 22 at same scale (scalebar 1 mm); scalebars 0.5 mm in figs 23 – 25.

FIGURES 26 – 27. Steginoporella discors n. sp. from Terra Nova station 944 (NHMUK 1967.2.8.127). 26, autozooids; 27, operculum, showing marginal cuticular teeth. Scalebars respectively 1 mm, 0.2 mm.

FIGURES 28 – 36. Opercula of New Zealand Steginoporella species showing presence and absence of sclerites on the inner face of the outer layer (localities in parentheses). 28, S. neozelanica (non-NIWA locality, Bare Island, Hawke’s Bay); 29, S. marcusi (D 896); 30, S. perplexa (Stn Z 8662); 31 – 33, S. magnifica, showing variation in sclerites from the same colony (Stn M 797); 34, S. discors n. sp. (Stn Z 9743); 35 – 36, S. lineata n. sp., showing opercula of smaller autozooid and larger avicularian B-zooid (Stn TAN 0205 / 64). All to same scale (scalebar 0.2 mm).