Adeonellopsis tasmanensis Liow & Gordon 2020, n. sp.

Adeonellopsis tasmanensis n. sp.

(Figs 3C, 8, 9 A–B; Tables 1, 2)

Etymology. Alluding to the occurrence of the species at two locations in the Tasman Sea.

Material examined. Holotype: Australian Museum U. 5792, from NIWA Stn I 85, 29.1317° S, 168.2500° E, 290 m, Norfolk Island shelf. Paratypes: Australian Museum U. 5793, same data as holotype; NIWA 144892, same data as holotype; NIWA 144894, 146154, from NIWA Stn P 239, 36.6917° S, 156.1917° E, 140 m, Gascoyne Seamount, Tasman Sea.

Diagnosis. Branches flattened, mostly 3–4 mm wide. Autozooids averaging 781 μm long, 340 μm wide. Au-tozooidal spiramen mostly with 6–8 pores. Moderately large suboral adventitious avicularium on every zooid; 1–2 small adventitious avicularia adjacent to suboral avicularium in some zooids, and additional ones budded distal to orifice and proximal to spiramen in ephebic zooids. Large vicarious avicularia at intervals adjacent to colony margins. Gonozooids large, with dimorphic orifices; spiramen like that of autozooids but larger, with 12–17 pores; 3 suboral avicularia, with up to 3 additional small accessory adventitious avicularia in ephebic gonozooids.

Description. Colony erect, rigid, maximum size not known; longest available fragment 11.4 cm. Distance between lateral branch bifurcations variable, sometimes quite long; branching typically in same plane. Colour in life unknown; dried fragments pale creamy-brown. Branch widths varying with age of colony, mostly 3–4 mm wide between bifurcations, wider just proximal to bifurcations. Autozooids arranged in quincunx; 9–14 longitudinal se-ries according to branch width.

Neanic autozooids (Fig. 8B) more or less rounded-subhexagonal to elongate-rectangular. Interzooidal boundaries indicated by thin lines of calcification in interzooidal furrows, bordered by 23–30 areolar pores in single series around entire zooidal margin; a few additional areolar pores on the inner side of the peripheral ones; marginal areolae sometimes merging as zooids acquire additional calcification. Average zooid length and width 781 μm and 340 μm, respectively.

Autozooidal peristomial orifice transversely oval to roundly D-shaped, becoming sunken within deepening peristome as zooids age. Multiporous spiramen (Fig. 8E) in frontal depression, more or less central or in proximal half of zooid; averaging 106 μm long, 80 μm wide; spiraminal pores 5–12, mostly 6–8, varying in size and shape but typically circular–oval, each mostly with 3–8 spokes that touch or overlap. Spiramen becoming deeply sunken and somewhat concealed as frontal shield thickens.

Adventitious avicularia (Fig. 8B, C) varying in size, position and orientation but having more or less the same form, i.e. elongate-triangular rostrum with narrow open-channelled acute tip and smooth raised (gymnocystal) margins, common rostral-opesial foramen, semicircular opesial margin, crescentic cryptocyst that is minutely granular bordering the opesia but smooth by gymnocystal margin; also no pivot bar but short curved pivot ridges at rostralopesial transition. Suboral avicularium moderately large, narrowly elongate, the rostrum elevated obliquely fron-talwards, directed distally or, more often, distolaterally, the tip reaching just past corner of orifice or overlapping it medially, or not quite reaching orifice. A small adventitious avicularium commonly adjacent to the mid-distal one, directed transversely or distolaterally; another such avicularium on opposite side in ephebic zooids, and additional ones budded distal to orifice and proximal to spiramen.

Large vicarious avicularia (Fig. 8A, C, F) at variable intervals adjacent to branch margins and proximal to bifurcations, averaging 541 μm long, with a terminal groove in the open rostral tip.

Gonozooids (Figs 8A, F; 9A, B) enlarged, averaging 881 μm long, 491 μm wide, occurring generally in small groups a few zooid-lengths proximal of a branch bifurcation or adjacent to a branch margin. Peristomial orifice larger and proportionately much wider (mean 210 μm) than autozooidal orifice, sometimes with denticulation (Fig. 8D) visible on inner proximal margin of peristomial orifice. Spiramen very large (Figs 8F; 9A, B), with 18–25 pores, each pore having 2–6 spokes that generally touch or overlap. Three suboral avicularia, the middle one directed distally or obliquely, the two flanking ones converging obliquely. Additional small adventitious avicularia may occur adjacent to the orifice and proximal to the spiramen in ephebic gonozooids (Fig. 9B).

Ancestrula and early astogeny not seen.

Remarks. The shallow coastal Victorian species Adeonellopsis australis MacGillivray, 1886 is morphologically very close to A. tasmanensis n. sp., having in common similar autozooids and adventitious avicularia, large gonozooids and large vicarious avicularia, but there are metric differences. For example, while ranges overlap, mean lengths of autozooids and suboral avicularia in A. tasmanensis n. sp. are very much greater. The most obvious difference concerns gonozooids. Whereas mean gonozooid length in A. tasmanensis n. sp. is 881 µm, the length of one in A. australis illustrated by Bock (2000) (image with scalebar) is 666 µm; the gonozooidal spiramen has 18–25 pores in A. tasmanensis n. sp. but only about 17 pores in A. australis. Adeonellopsis tasmanensis n. sp. can have a similar complement of zooidal adventitious avicularia on ephebic zooids as there are on neanic zooids in the coastal Victorian species Adeonellopsis foliacea MacGillivray, 1886, which, however, has a foliaceous colony form and far fewer autozooidal spiraminal pores (only 3–4 vs 5–12 in A. tasmanensis n. sp.).

Adeonellopsis tasmanensis n. sp. has a somewhat similar colony form to A. macewindui n. sp. and A. wassi n. sp. but differs, inter alia, in mean zooid size and gonozooid spiramen number (Tables 1, 2). Overall, A. tasmanensis n. sp. has the largest suboral and vicarious avicularia, and the largest number of gonozooidal spiraminal pores of any of the new species described herein.

Distribution. Norfolk Island shelf (Australian territorial waters) and Gascoyne Seamount, Tasman Sea, 140– 290 m.