Rhabdopleura striata Schepotieff, 1909

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 : 337

Rhabdopleura striata Schepotieff, 1909 ( Fig. 4E, F )

Type locality. Kankesanturai , northern Sri Lanka, 2‒3 m depth on hardstone .

Key features. Inception of ringed erect tubes is indirect. The type colony was described as 7‒8 cm long, with erect-tube height 11‒12 mm and diameter 1 mm; the zooid is 1.0‒ 1.5 mm long and yellowish with pigment spots. Creeping tubes are almost straight, with few blind-ending lateral branches, all (with few exceptions) along one side only; these are proximally adherent for 2‒3 mm before rising perpendicularly. Unique to R. striata is a wedge or web of cuticle, with fusellar sutures, in the angles where lateral branches diverge from the creeping tube ( Fig. 4F ). Fusellar collars are weakly developed, “so that at low magnification the living tubes appear clearly longitudinally striped [i.e. having aligned vertical fusellar striae], but not transversely ringed” [“so dass bei schwacher Vergrösserung die Wohnröhren deutlich längsgestreift, nicht aber quergeringelt erscheinen” ( Schepotieff 1909, p. 431)]. There are 8‒10 ‘panels’ in each fusellar ‘circle’ [between fusellar collars]. The number of ‘circles’ varies from 150 to 500 depending on tube length. Fusellar height is 100‒125 μm.

Comment. Rhabdopleura striata is exceptional for its large tubes and zooids, with aligned longitudinal striae in ‘panels’ within the fusellae. Furthermore, in contradistinction to R. normani and similar species with indirectly budded erect tubes, side branches issue almost exclusively from just one side of the creeping tube.

Figures

FIGURE 4. Original illustrations of described species of Rhabdopleura characterized by indirect inception of ringed erect tubes from creeping tubes via an intervening adnate portion that comprises a blind-ending branch. A, Rhabdopleura normani (from Allman 1869, pl. 8, fig. 1). Note that most of the colony is adherent; only the ringed tubes (rt) are erect, the proximal part of each side branch (ppsb) is adherent and the oblique sutures are not shown. B, schematic interpretative depiction of R. normani (after Andres 1977). C, D, Rhabdopleura grimaldii (from Jullien 1890, p. 181); note that ringed erect tubes (rt) are mostly lacking, with only the adherent proximal parts of side branches (ppsb) present. D is a cropped part of C to show the proximal parts of two side branches, with fusellar sutures and Jullien’s putative ‘very fine tubes’ (vft)—actually the side walls of the tapering pectocaulus, the proximal end of which is transparent, hence the apparent gap between it and the pectocaulus of the creeping tube. E, F, Rhabdopleura striata (from Schepotieff 1909, pl. 7, figs 2, 7); E shows longitudinally striated erect parts of side branches; oblique sutures on prostrate parts omitted in E but shown in F, with characteristic web of fusellar sutures (wfs) in branch angles from main creeping tube. G, Rhabdopleura manubialis (from Jullien & Calvet, 1903, pl. 1, fig. 2) with dormant bodies (db).