Rhabdopleura grimaldii Jullien, 1890

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 : 334-337

Rhabdopleura grimaldii Jullien, 1890 ( Figs 4C, D ; 6A‒D )

Type locality. Off the southeastern tip of Pico Island, Azores, 318 m, on dead shell and bryozoans [38.4000° N, 28.0239° W in Stebbing (1970a, p. 211), the original Paris meridian corrected to Greenwich] .

Key features. Inception of ringed erect tubes is indirect. Jullien (1890) described the 1‒2 cm-long colony as consisting of a primary bifurcating creeping tube (‘stolon’) containing the pectocaulus (‘filet chitineux’), with short blind side branches on either side, each comprising an adherent portion (‘zooecium’) with zigzag sutures, terminating in an erect ‘péristomie’, with annular fusellar collars. This arrangement corresponds to that in R. normani , i.e. zooidcontaining side tubes are proximally adherent before bending at an angle upwards. ‘Zooecia’ are said to be a little wider than the stolon. The main distinguishing character of this species was described as two very thin tubes (‘tubes très fins’) in the adherent proximal parts of the blind side branches, reflected externally as two dark-brown lines (‘lignes brun foncé), the distal ends of which converge without meeting at the proximal end of the ‘péristomie’ ( Fig. 6C, D ). Oblique sutures with zigzag angles were described as restricted to the ‘zooecium’; the primary creeping tube itself was ‘dépourvue de stries’ (free of streaks), with zooids retracting into the adherent portion of the side branches as in R. normani . Annulated erect tubes were mostly missing from his material; some are broken and only one appears intact in his drawing ( Fig. 4C , rt).

Comment. The Muséum National d’Histoire Naturelle (MNHN), Paris, was contacted in the hope that photos could be made of the species (MNHN-IB-2014-386). Dr Pierre Lozuet of the Collections Department ( Direction des Collections ) sent reflected-light images, which included two high-resolution close-ups, with scale bars. The unique syntype is on a worm tube. It is dry and the overall colony seems to bear little resemblance to Jullien’s original illustration. Additionally, most of the creeping tubes are highly transparent and reflective, rendering details like fusellar sutures problematic. Notwithstanding, the images yielded enough information to discern key features and to make some measurements .

Primary creeping tubes (convexity) are 146‒167 (158) μm wide (n = 5), with pectocaulus width 21‒44 (31) μm (n = 8). Contra Jullien, primary creeping tubes have surface fusellar sutures; a sequence of nine point-to-point zigzag angles was measured, ranging from 63‒76°, with mean 70° and mode 65°. In contrast, the adherent parts of blind side branches have a higher mean convexity width [134‒201 (177 μm), n = 5]. The most striking character, which is unique to this species, is the pectocaulus of an adherent side branch. It is defined by a pair of thin brown lines (its side walls) that converge toward the base of the erect ringed tube ( Fig. 6C, D ). Because the central part is thin-walled and clear, Jullien (1890) and Jullien & Calvet (1903) interpreted the thin brown lines as very fine tubes. These authors correctly illustrated an apparent ‘gap’ ( Fig. 4D ) at the point where the brown pectocaulus diverges from the creeping tube into a side branch. At this point, the pectocaulus apparently becomes thinner, wider, and nearly transparent as it transitions into the side branch, with only its side walls clearly showing. Schepotieff’s (1907, pl. 33, figs 5, 9) cross sections of the pectocaulus in R. normani show side walls thickening at their base; this would account for the frontal appearance, in R. grimaldii , of the paired thin lines, each being a side wall. In this species, pectocaulus width prior to distal narrowing is 51‒74 (63) μm; the side walls (the so-called ‘tubes très fins’) are 12‒14 (13) μm (n = 4), too narrow for them to constitute converging paired pectocauli (an alternative interpretation). Presumably the distal tapering of the pectocaulus allows it to converge into the gymnocaulus of the zooid. [Actual zooids were not seen, however.] Erect ringed tubes are 92‒117 (104) μm diameter between fusellar collars (n = 8) and fusellus height is c. 19‒22 μm (n = 2).

Surface fusellar sutures of the adherent parts of side branches differ from those on primary creeping tubes, being closer together and having smaller zigzag angles. Two sequences of nine zigzag angles were measured, collectively ranging from 33‒60°, mean 46°, mode 35°. [In Jullien’s drawings, zigzag angles on side-branches are 40‒54°, mean 47°, mode 50° (n = 18), suggesting that his depictions of zigzag angles were pretty reliable.]

Our conclusion is that R. grimaldii is a highly distinctive species that cannot be synonymized with any other.

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).

FIGURE 6. Rhabdopleura grimaldii Jullien, 1890 (A‒D, syntype MNHN-IB-2014-386) and R. manubialis Jullien & Calvet, 1903 (E, syntype MNHN-IB-2014-387). A, B, oblique views of two erect ringed tubes. C, adherent proximal part of a side branch (apsb), with a tapering pectocaulus (tp) (its side walls appearing as converging brown lines) and the broken base of an erect tube (bbet). D, similar to C, but also showing the creeping tube (ct) from which the broader side branch originated; note the faint outlines of oblique sutures on the creeping tube and side branch. E, erect ringed tube. Scale bars: A, B, 100 μm; C‒E, 200 μm. Images cropped from photos supplied by Pierre Lozuet, MNHN, Paris.