Rhynchozoon zealandicum, Gordon, 2009

Gordon, Dennis P., 2009, New bryozoan taxa from a new marine conservation area in New Zealand, with a checklist of Bryozoa from Greater Cook Strait, Zootaxa 1987, pp. 39-60 : 48-50

Rhynchozoon zealandicum n. sp.

( Figs 22–28 )

Rhynchozoon bispinosa [sic]: Gordon 1967: 60, fig. 36. Non Lepralia bispinosa Johnston, 1847 .

Rhynchozoon rostratum: Gordon 1967: 60 , fig. 37; Gordon 1970: 309 et seq. Non Lepralia rostrata Busk, 1856 .

Rhynchozoon larreyi: Powell 1967: 362 , pl. 14f; Uttley & Bullivant 1972: 47; Gordon & Ballantine 1977: 127; Gordon 1989: 74, pl. 43, B–D. Non Cellepora (?) larreyi Audouin, 1826 .

Material examined. Holotype: NIWA 46365 . Paratypes: NIWA 46366 , 56367 . All types from low-tidal substrata, by jetty, south side of NIWA reclamation, collected by D.P. Gordon 16 May 2008 .

Etymology. This taxon is the most widespread and abundant of the New Zealand Rhynchozoon species.

Description. Colony encrusting, pale pinkish-white in colour, sometimes with a reddish cast in older parts of colonies. Zooids around 0.39–0.67 mm long and 0.22–0.37 mm wide as measured from normal, recumbent zooids near colony margin, these tending to suberect and irregularly disposed in colony centre. Frontal shield smooth or faintly textured, typically porcellanous, with 2–5 areolar pores along each lateral margin. Primary orifice wider (mostly in range 0.10–0.12 mm) than long, with fine denticulation around margin of anter, sinus broadly U-shaped. Peristome variable, rim typically developing 3 mucrones, largest median and sloping into frontal shield, other 2 lateral to orifice, smaller and more pointed; the 3 umbones becoming less pronounced as secondary calcification develops around them, with orifice appearing more irregular. If suboral avicularium present, a pseudosinus tends to be in evidence between lateral mucro and opesial end of avicularium. Oral spines not seen. Suboral avicularium relatively large, orientated transversely, with complete cross-bar and triangular mandible that is 0.06 mm long; angular process often projecting from proximal corner of avicularium into space above zooidal operculum. Additional avicularia may occur frontally, sometimes as many as 1 per zooid locally in colony, otherwise quite rare; these 0.13 mm long, mandible acute, generally directed proximally or obliquely so. Ovicell recumbent, becoming subimmersed in secondary calcification, with transversely oval frontal exposure of endooecium and very short wide labellum.

Remarks. This species is widespread around New Zealand, from the mid-tide zone to 235 m deep on the continental shelf ( Gordon 1989) and from Spirits Bay to Puysegur Bank on hard rocky and shelly substrata. Gordon (1970) noted that colonies in the Leigh area (misidentified as R. rostratum ) contained deep-orange embryos in their ovicells year round, with a peak from November through May and fewest in June and July. It has in the past been misidentified as Rhynchozoon larreyi ( Audouin, 1826) , a tropical Indo-Pacific species first described from the Red Sea. Examination of topotypic material kindly donated by Heinrich Ristedt shows that this species is indeed very similar but has instead a rounded V-shaped sinus; the frontal shield is also inclined to develop coarse tuberculation in older parts of the colony. Powell (1967) mentioned four oral spines in marginal zooids from the Three Kings Islands; these were not seen in the present material. Rhynchozoon zealandicum is very similar to R. rostratum (Busk, 1855) (type locality Mazatlan, Mexico) but that species differs in having a more V-shaped sinus and the narrow band of ectooecium proximal to the ovicellular tabula is not continuous. Dick & Mawatari (2005) have remarked on the challenge of circumscribing Rhynchozoon species based on taxonomically informative characters owing to inferred geographical, ecophenotypic, and intracolony variation that is difficult to distinguish from interspecific variation. For example, their Rhynchozoon sp. form A from Ketchikan, Alaska, closely resembles R. zealandicum in the characters of the orifice, ovicell, and frontal avicularium, but marginal zooids have a pair of stout oral-spine bases and the suboral avicularium lacks an angular process. They point out the utility of 16S mitochondrial ribosomal RNA in discriminating co-occurring forms of Rhynchozoon that appear morphologically similar.

Figures

FIGURES 22–28. Rhynchozoon zealandicum n. sp. 22, Surface of colony from margin to centre showing the change in orientation of zooids in the centre of the colony owing to frontal budding. 23, Developing zooids at the colony margin showing the distribution of pore-chambers. 24, Orificial view of zooids near the colony margin showing suboral avicularia. 25, Recumbent zooids showing the peristomial processes. 26, Frontally borne adventitious avicularium. 27, Ovicells showing frontal ectooecial tabula and short broad labellum. 28, Primary orifice. Scale bars: Fig. 22 = 1 mm; Figs 23–27 = 100 µm; Fig. 28 = 20 µm.