Rhabdopleura chathamica, Gordon & Randolph Quek & Huang, 2024

Gordon, Dennis P., Randolph Quek, Z. B. & Huang, Danwei, 2024, Four new species and a ribosomal phylogeny of Rhabdopleura (Hemichordata: Graptolithina) from New Zealand, with a review and key to all described extant taxa, Zootaxa 5424 (3), pp. 323-357 : 339

Rhabdopleura chathamica n. sp.

( Fig. 7A‒F )

Material examined. Holotype: NIWA 161214 , Stn TAN0104/333, Chatham Rise, New Zealand, 42.7183° S, 179.9095° W, 1008‒1075 m, 20 April 2001 . Paratype: NIWA 90265 , same data as holotype. Both reconstituted from originally dry material .

Etymology. Alluding to the provenance of the species on the Chatham Rise, New Zealand.

Diagnosis. Erect ringed tubes produced by short adnate branches from creeping tubes and separated by intervals of 1.2‒2.1 mm mainly on one side of creeping tubes; mean erect-tube diameter 132 μm, mean fusellus height 22 μm. Colony with sparse secondary runner branches, spreading to at least 9 mm length. Zigzag sutures of creeping tubes conspicuous, zigzag slightly less than one third convexity width, sutures slightly wider apart than those on adnate side branches; zigzag angles 44‒66° on main creeping tubes, 33‒61° on short adnate branches.

Description. Erect-tube inception indirect via short adnate side branch from a creeping tube, the erect tube constituting the terminus of the short branch. Colony encrusting surface of dead coral, comprising one main creeping tube with sparse secondary branches of creeping tube, these producing short blind side-branches, each side-branch composed of a proximal adherent portion and a distal erect tube ( Fig. 7A, B ). Maximum length of incomplete colony (paratype) 9 mm, with lateral spread to c. 4 mm owing to lateral creeping tube diverging from main creeping tube; main creeping tube relatively straight with only moderate curvature. Blind side-branches produced at intervals of c. 1.2‒2.1 mm, mainly on one side in the present material.

Creeping tubes with convex part 149‒205 (186) μm (n = 11) wide, with flattened marginal lamina along both sides ( Fig. 7B ), also of variable width [28‒44 (37) μm, n = 13], its edges often diffuse and not well defined. Surface fusellar sutures conspicuous ( Fig. 7E ), with point-to-point zigzag angles of 44‒66 (55)°, mode 55° (n = 50); zigzag sequence narrow, occupying only c. 27‒30% of convexity width, with zigzag components straight or gently curved. Pectocaulus running along floor of creeping tubes, including under dormant bodies within tubes, 22‒29 (25) μm wide (n = 7).

Blind-ending side branches generally straight, rarely curving, budded at right angles or obliquely from creeping tube, with adherent portion 424‒603 (499) μm long (n = 8), convexity 170‒211 (192) μm wide (n = 8), margin 28‒44 (37) μm wide (n = 13). Oblique sutures a little more closely spaced ( Fig. 7F ) than on main creeping tube, with smaller zigzag angles [33‒61 (45)°, mode 40 (n = 22)].

Erect tubes from side branches ( Fig. 7C, D ) all broken and somewhat fouled, the longest 598 μm. Tube diameter between fusellar collars 109‒159 (132) μm (n = 9), collars moderately projecting circumferentially around tube [4‒11 (7) μm, n = 17], lightly to moderately crinkled and horizontal to oblique, with variable fusellus height [12‒34 (22) μm (n = 28), fuselli generally shorter in proximal third part of tubes; number of fusellar collars in 500 μm of erect tube c. 20 (n = 2).

Dormant bodies not seen. Founding individuals (siculae) and zooids not seen.

Remarks. The holotype and paratype colonies grew on a fragment of the ahermatypic scleractinian coral Gonioporella dumosa . The colonies cannot be wholly seen in any one image because they follow the curvature of the cylindrical coral substratum. Rhabdopleura chathamica n. sp. is the only species seen so far in New Zealand waters with indirectly budded erect tubes and is therefore easily recognizable from the blind-ending side branches that occur along one or both sides of creeping tubes. It seems to be a rare species. Much material of G. dumosa from the same and nearby localities was examined but no other specimens were found. If erect ringed tubes are short or broken off only the thin pectocaulus is plainly seen; creeping tubes are transparent and surface details are hard to discern unless light is reflected at a certain angle. On the other hand, SEM renders creeping tubes plainly visible.

At 1008‒1075 m, R. chathamica n. sp. is the deepest-occurring species so far recorded, exceeding the 896 m depth reported for R. normani on Desmophyllum pertusum coral at the edge of the Celtic Sea shelf, northeast Atlantic ( Stebbing 1970a, Table 2).

Figures

FIGURE 7. Rhabdopleura chathamica n. sp., A‒C, F, paratype 90265; D, E, holotype 161214: A, part of colony showing three blind side branches, the proximal part of which is adherent; only one ringed erect tube (et) remains. B, close-up of middle side branch in A; note part of the pectocaulus/black stolon (bs) seen through a tear in the cuticle. C, the longest zooid seen, somewhat fouled and partly twisted in profile. D, non-fouled part of another erect tube showing well-developed fusellar collars. E, fusellar sutures on surface of creeping tube, with some point-to-point suture zigzags highlighted. F, close-up of fusellar sutures seen on adherent tube in B. Scale bars: A, 1 mm; B, 300 μm; C, F, 100 μm; D, 50 μm; E, 200 μm.