Rhabdopleura francesca, 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 : 340-342

Rhabdopleura francesca n. sp.

( Figs 8A‒H , 9A )

Rhabdopleura sp. ‘Spirits Bay’: Gordon et al. 2023: pp. 4, 7, 13, figs 2c, 3b, 8a-h.

Material examined. Holotype: NIWA 158157 , Stn Z 9708, Three Kings shelf north of Spirits Bay (Piwhane), 34.3390° S, 172.7410° E, 59 m, 29 January 1999, in ethanol . Paratype: NIWA 162577 , same data as holotype .

Etymology. Honorific for Dr Francesca Strano, acknowledging her interest in this study and in recognition of her work on Rhabdopleura recondita ; her given name used in apposition.

Diagnosis. Erect ringed tubes budded directly from surface of creeping tubes. Colony ramifying over dead shell, up to 7 cm length or diameter. Erect tubes spaced 675‒808 μm apart, mean erect-tube diameter 119 μm, mean fusellus height 40 μm. Zigzag sutures of creeping tubes not conspicuous, zigzag traversing half to three-quarters of convexity width; zigzag angles 33‒51° on straighter, narrower sections of creeping tube, otherwise 26‒54°, more divergent on wider sections of tube associated with dormant bodies, the latter imparting a dashed appearance to many tubes along their length when viewed by light microscopy.

Description. Inception of ringed erect tubes is direct, from surface of creeping tubes. Colony encrusting surface of dead shell, ramifying mostly irregularly over surface ( Fig. 8B ), with curved, sinuous or straight sections, creeping tubes branching often at right angles at non-regular intervals ( Fig. 8C ), spreading up to at least 7 cm across substratum, forming conspicuous dark-brown to black continuous or dashed tracery.

Creeping tubes variable in width ( Fig. 8G, H ); convex part of tube 185‒325 (257) μm (n = 31) wide, with flattened marginal lamina along both sides, also of variable width [24‒113 (71) μm, n = 31], its edges smooth, entire or diffuse; creeping tubes tending to be widest in vicinity of dormant bodies; branching at angles of c. 30‒90°. Surface fusellar sutures on straighter, more parallel-sided sections of tube (e.g. Fig. 8H ) with point-to-point divergence (zigzag) angles of 33‒51 (42)°, mode 45° (n = 23); range of angles more divergent [26‒54° (mean 37°)] on broader, more laterally convex sections of tube typically associated with dormant bodies; zigzag sequence occupying half to three-quarters of convexity width, with zigzag components curved or, less often, straight. Pectocaulus running along floor of creeping tubes, including under ‘dormant buds’ within tubes ( Fig. 8F ), 28‒46 (36) μm wide (n = 15).

Erect tubes up to 3382 μm long, spaced at distances of c. 675‒808 (750) μm along creeping tubes. Tube diameter between fusellar collars 101‒140 (119) μm (n = 39), most of tube with fairly evenly spaced fusellar collars, these generally weakly projecting circumferentially around tube [3.3‒13.8 (6.4) μm, n = 50], microscopically crinkled and horizontal or slightly oblique over most of tube length, more irregular in distalmost and proximalmost parts of tubes. Distance between fusellar collars (i.e. fusellus height) in standard section of tube 19‒60 (40) μm (n = 38). Number of fusellar collars in 500 μm of erect tube 10‒12 (11) (n = 11).

‘Dormant buds’ abundant, mostly parallel-sided or curved, rounded at each end, located serially along creeping tube, each proximal to an erect tube and visually separated from adjacent ‘dormant buds’ by a section of pectocaulus; dormant bud semi-solid, made up of firm rounded globules ( Fig. 8F ).

Founding individuals (prosiculae and zooids) not seen.

Remarks. Rhabdopleura francesca n. sp. occurs on the Three Kings Shelf, an area of seafloor off the northern tip of New Zealand’s North Island where R. annulata was discovered. Gordon et al. (2023) examined by SEM a tiny portion of the preserved holotype colony as well as Norman’s (1921) slides of R. annulata . Like R. francesca n. sp., R. annulata has direct-frontal growth of erect tubes, but it differs principally in erect-tube diameter, which is smaller and non-overlapping compared to that in R. francesca [167‒200 (180) μm vs 101‒140 (119) μm] and in having extremely wide zigzag sutures that extend across the full width of the creeping tube onto the flattened marginal laminae (cf. half to three-quarters of creeping-tube width in R. francesca n. sp.). This latter character was consistent in R. annulata from Queensland ( Ramírez-Guerrero et al. 2020, fig. 1C) and tube metrics conformed as well. Norman (1921, p. 98) also specifically stated that creeping-tube width and erect-tube diameter were the same in R. annulata , which is not the case in R. francesca n. sp., in which erect-tube diameter ranges from 43‒68% of creeping-tube width. Indeed, the phylogenetic results agree on the distinction between R. annulata and R. francesca n. sp., with the phylogeny reconstructed based on both mitochondrial genomes and 16S+18S rRNA concatenated sequences recovering them in separate lineages ( Fig. 3 ).

The term ‘dormant buds’ was introduced by Stebbing (1970b, p. 210) for conspicuous ovoid or spherical masses of yolky granules within creeping tubes. Each is formed at the proximal end of the contractile stalk of a zooid near the septum, becoming enclosed in a dark capsule. Inasmuch as functional feeding zooids can occur within erect tubes distal to the ‘dormant buds’, it may be that they serve as both active and dormant nutrient reserves within a colony. They are abundant in R. francesca n. sp.

Figures

FIGURE 3. Maximum likelihood phylogeny for Rhabdopleura reconstructed on: A, concatenated 16S+18S rRNA genes; B, 13 mitochondrial protein-coding genes. Numbers adjacent to nodes represent bootstrap support (≥ 50) /posterior probability (≥0.8) values.

FIGURE 8. Rhabdopleura francesca n. sp., A‒E, holotype NIWA 158157; F‒H, paratype NIWA 162577: A, complete erect tube 2.5 mm long. B, holotype, possibly comprising more than one colony, on broken scallop shell. C, close-up of B showing that the black tubarium tracery in A is accentuated by continuous series of what look like dormant buds lying along black stolons. D, section of tube bracketed in A. E, apertural end of another erect tube. F, black stolon emergent from a ‘dormant body’ in part of a creeping tube. G, H, variations in creeping-tube width and fusellar patterning, the latter typically weak and thinly developed throughout colony; some point-to-point suture zigzags highlighted. Scale bars: A, 1 mm; B, 2 cm; C, 3 mm; D‒F, 100 μm; g, h, 200 μm.

FIGURE 9. Rhabdopleura francesca n. sp.: A, section of creeping tube of holotype with a broken erect tube; note the small erect-tube diameter relative to the width of the creeping tube. Rhabdopleura decipula n. sp.: B, holotype NIWA 162592 (left) and paratype 1 (NIWA 161212) colonies on broken shells; C, reflected-light image of part of a paratype 2 colony (NIWA 161213) seen in transparency on smooth shell, showing a loop of one creeping-tube branch curving back on itself, with a narrow crossconnection (cc) of the pectocaulus; erect tubes and zooids (z) and a dormant body (db) also seen. D, SEM image of same colony at lower magnification, with branch loop in C at top right. E, another part of same colony seen in transparency, showing a zooid inside a creeping tube to the left (distal) of a dark dormant body. Scale bars: A, 500 μm; B, 10 mm; C, 1 mm; D, 2 mm; E, 400 μm.