Rhabdopleura annulata Norman, 1921

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 : 338

Rhabdopleura annulata Norman, 1921 ( Fig. 5B )

Type locality. Western Three Kings Shelf , northernmost New Zealand, 34.4833° S, 172.0500° E, 549 m depth on a stone .

Key features. Inception of ringed erect tubes is direct. Erect tubes arise directly from the upper surface of primary creeping tubes, having the same width/diameter (erect-tube diameter 169‒213 μm—adding together Norman’s dimensions for internal tube diameter and wall thickness between collars). Erect-tube spacing was described as variable, being close together or 3‒8 mm distant from each other. Very widely transverse zigzag fusellar sutures occur on the creeping tube, with zigzag angles extending onto the flat lateral margins. Mean fusellus height was stated to be 50 μm.

Comment. Gordon et al. (2023, fig. 3a, 6a, b) illustrated and measured a tiny part of the holotype specimen (SEM and LM images), determining that erect tubes were 167‒200 μm diameter (mean 180 μm) between collars, with fusellus height 38‒54 μm (mean 45 μm) and zigzag angles on creeping tubes were 25‒46° (mean 34°). Johnston’s (1937) record of R. annulata from Port Willunga, south of Adelaide, South Australia, was not illustrated and Shepherd (1997) did not cite the provenance of his illustrations of Rhabdopleura in a handbook on marine invertebrates of southern Australia, including Tasmania, so no firm conclusion can be drawn on the identity of southern Australian material. Johnston stated that tube diameter was 265 μm, larger than reported for the New Zealand type locality. Ramírez-Guerrero et al. (2020) recorded R. annulata from Heron Island, Great Barrier Reef.

Figures

FIGURE 5. Original illustrations of three described species of Rhabdopleura characterized by direct-frontal inception of ringed erect tubes (A‒C). Erect-tube inception in R. compacta (D‒F) appears to be a form of indirect erect-tube inception. Note that the direction of zooid budding is the same in A to C. A, Rhabdopleura mirabilis (from Sars 1872, pl. 1, fig. 5). B, Rhabdopleura annulata (from Norman 1921, fig. 4). C, Rhabdopleura recondita (after Beli et al. 2018, fig. 2C). D‒F, Rhabdopleura compacta (respectively after Hincks 1880, pl. 72, fig. 8; Stebbing 1970b, fig. 1; Stebbing 1970a, fig. 3).