Rhabdopleura normani Allman

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 : 331-332

Rhabdopleura normani Allman in Norman, 1869

( Fig. 4A, B )

Type locality. Outer Haaf, Unst, Shetland, U.K. at 93 fm (170 m) ( Norman 1869) or 90 fm (~ 165 m) on dead shell ( Allman 1869). Burdon-Jones (1954) cited the locality as c. 40 miles east of the Whalsay Skerries, i.e. c. 60.4° N, 0.48° E.

Key features. Inception of ringed erect tubes is indirect; blind-ending side branches comprise, for about half their length, an adherent portion that abruptly bends at a right angle upwards as an annulated tube ( Fig. 4B ; see Andres 1977, fig. 1, interpretative). Allman (1869, p. 58) noted that adherent and erect parts of each side branch are of the same diameter ( Fig. 4A ) and illustrated the median zigzag suture (ibid., pl. 8, fig. 4), which occupies only about a quarter of tube width. Measured from his drawing, zigzag angles are 54‒61°, mean 57°, with mode 55° (n = 11). Lankester (1884, pl. 39, fig. 1) also illustrated zigzag angles, having a larger range of 36‒60° owing to sinuous bending, with mean 47° and mode = 45° (n = 23), and also showed (ibid., pl. 41, fig. 2) a short ‘permanently closed’ chamber of creeping tube with zigzag angles 33‒43°, mean 40° and mode 40° (n = 8).

Comment. Allman’s material seems not to be represented by a type specimen. There is an unregistered slide in the collection of the Natural History Museum, London, labelled “ Rhabdopleura Normani, Allman. (fide A.M. Norman): no doubt from Shetland ”, with no other information (A. Waeschenbach, NHM, pers. comm., 9 Feb. 2024). The slide contains a dried piece of shell and is inadequate to establish that it represents the non-living material that Allman examined and illustrated. The species needs re-examining on the basis of topotypic material and a neotype established. Other slides (plus wet specimens) of putative R. normani from the NE Atlantic pertain to Hardanger Fjord, Norway. Lankester’s (1884) material, which has aways been regarded as R. normani , came from Hardanger Fjord (Lervik, Stordoe Island), at 40 fm (73 m) on Ascidia mentula . Lankester (1884, p. 623) noted that in 1879 A.M. Norman collected the species at 150 fm (274 m) from the same general locality on Desmophyllum pertusum coral (as Lophelia prolifera ). Unlike Allman, Lankester (1884, p. 630, pl. 38) was able to study the living animal, describing the zooid as having “black and orange-brown pigment, so as to give a spotted leopard-like appearance to the animal.” In comparing R. normani with Rhabdopleura mirabilis ( Sars, 1872) (see below), Lankester (1884, p. 626) concluded: “I do not think that Sars has given sufficient reason to lead to the conclusion that his Rh. Mirabilis is anything more than a variety of Rh. Normani .” Having said that, he did also admit that R. mirabilis does not “quite agree … since the polypide tubes are for no part of their course recumbent, but spring directly from the axis [creeping tube] at right angles to it.” He attributed this lack of correspondence in colony form to the different substratum.

Given its purported common distribution in the northeastern Atlantic (Burdon-Jones 1954), R. normani has been surprisingly little illustrated and redescribed. Maletz et al. (2016), however, photographed erect ringed tubes of R. normani in transparency, sourced from Bergen, Norway, with a scale bar indicating external tube diameter between fusellar collars as 143‒154 (148) μm (n = 10), and fusellus height 24‒41 (33) μm (n = 20).

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).