Holotype : SAM A021260, from Station No MAD 39 FFF; 46°59'45"S, 38°00'39"E, depth 360–376 m, Marion and Prince Edward Island, South Africa, collected by bottom dredge, University Marion Island Survey, coll. 26 August 1987 by M. Branch.

Paratypes : SAMC A094445, 1 specimen complete, prepared for SEM, and 3 incomplete specimens, with parts of body wall dissected and empty tubes. All paratypes collected from same location as holotype. All material fixed in formalin and then transferred to 70% alcohol.

The specific epithet brevis is Latin for “shallow”, which refers to the type locality of new species, collected in relatively shallow waters compared to Petta assimilis, which is known from a nearby area but in much deeper water.

Holotype pale in colour except for golden paleae and sand grains visible through the body wall. Body cylindrical, tapering before scaphe (Figs 2A, B, 3A). Length 15 mm (20) including paleae and scaphe, maximum width 3 mm (3).

Figure 2. 

Petta brevis sp. nov., holotype (SAM-A021260) A dorsal view of whole body B ventral view of whole body C ventral view of anterior end D dorsal view of anterior end E close up of left branchiae F dorso-lateral view of posterior end G ventral view of posterior end H close up of scaphal hooks. Abbreviations: af, anal flap (plate); an, anus; br, branchiae; bt, buccal tentacles; cv, cephalic veil; dlp, dorso-lateral pad; dms, dorsal margin of scaphe; lel, lateral ear-shaped lobe; nec, neurochaetae; nep, neuropodium; noc, notochaetae; op, operculum; or, opercular rim; p, paleae; s, segment; sc, scaphe; sh, scaphal hooks; tc, tentacular cirri; vl, ventral lappet.

Cephalic veil semi-circular, free from operculum, with smooth lateral margins, distal (anterior) end thin, folded over with smooth margins (Fig. 2A–C). Pair of lateral ear-shaped lobes adjacent to dorsal side of cephalic veil (Fig. 2C). Buccal tentacles numerous, thick, with deep longitudinal grooves arising around buccal cavity (Figs 2B, C, 3C).

Operculum semi-circular, surface tessellated and slightly inflated, with lateral and dorsal margins slightly elevated but smooth (Figs 2A, D, 3C). Two rows of 13 pairs of golden coloured paleae, some broken but arranged in a fan shape, differing slightly in length, outer ones shorter and thinner than inner ones on each row, slightly curved dorsally, with blunt tips (Figs 2C, D, 3C).

Figure 3. 

Petta brevis sp. nov., SEM of paratype (SAMC-A094445) A ventral view of whole body B ventral view of anterior end C dorsal view of anterior end D ventral view of posterior end with distorted scaphe E notochaetae F close up of uncini. Abbreviations: af, anal flap (plate); an, anus; br, branchiae; bt, buccal tentacles; cv, cephalic veil; dlp, dorso-lateral pad; mat, major teeth; nec, neurochaetae; nep, neuropodium; noc, notochaetae; nop, notopodium; op, operculum; or, opercular rim; p, paleae; s, segment; sc, scaphe; tc, tentacular cirri; vl, ventral lappet.

First pair of tentacular cirri extending to about halfway along the outer paleae, slightly annulated with swollen base tapering to long thin tip arising from base of opercular margin and paleal ridge (Figs 2A–D, 3B, C). Pair of blunt-tipped triangular ventral lappets present just laterally to first pair of tentacular cirri (Figs 2C, 3A, B).

Second pair of tentacular cirri similar in length to first pair but thinner and with base less swollen than that of first pair (Figs 2A–D, 3B, C), inserted slightly dorsally on mid lateral connecting ridge of segment 2. Segment 2 with pair of broad ventro-lateral lobes separated by a broad and deep mid-ventral groove; each lobe with six pairs of triangular lappets, two mid ventral ones largest (Figs 2B, C, 3B, C).

Segments 3 and 4 with two pairs of similar-sized branchiae, those of segment 3 slightly displaced ventrally (Figs 2A, D, 3C). Each branchia with large basal hump and with about six loose, flat lamellae (Fig. 2D, E). Segment 3 with raised ventral ridge with pair of broad ventro-lateral lobes and pair of rectangular mid-ventral lobes, mid-ventral lobes with rounded margins (Figs 2C, 3B). Segment 4 with slightly raised ventral margins with slight mid ventral indentation, but ventral margins less glandular than those of segment 3 (Figs 2B, C, 3A, B). Pair of dorso-lateral pads small and smooth, arising from dorsal side of notopodia on segment 5 (Figs 2D, 3C), but distorted on segment 5 of holotype.

Discrete raised ventral glandular lobes (pads) on segments 2–7, decreasing in size and elevation posteriorly with slight mid-ventral indentation (Figs 2C, 3B).

Notopodia of segment 1 with paleae, and notochaetae from segments 5–21 (17 pairs). Notopodia of segments 5–7 smaller and with smaller notochaetae (Figs 2D, 3C); notopodia of segments 8–13 relatively large with long chaetae; following notopodia decreasing posteriorly in size, length of notochaetae similarly decreasing. Notopodia with 2 rows of different capillary notochaetae; one with distal serrated wings, anterior surface covered with numerous minute spines from below wing to about mid-basal portion of chaeta; another tapering to acute tip without wings, anterior surface covered with numerous spines from mid-length to tip (Fig. 3E).

Neuropodia developed from segment 8 (Figs 2B, C, 3A, B), continuing to scaphal plate, with slightly raised tori. Neurochaetae (uncini) arranged in single transverse row on each torus. Uncinus with two main teeth, followed by several rows of numerous small teeth (Fig. 3F) and a large peg with blunt tip embedded into torus. Neuropodia of segment 21 with enlarged posterior lobe (Fig. 3A).

Scaphe long, ovoid, flattened dorsally, inconspicuous constriction on posterior segments. Lateral margins rolled dorsally, with six pairs of lobes; first pair largest, connected to dorsal margin of scaphe; posterior lobes narrow, triangular, almost of equal size; dorsal margin of scaphe smooth (Figs 2F, G, 3D). Anal flap triangular, without an anal cirrus. Scaphal hooks amber-coloured, left 9 and right 10 on holotype, arising from both sides of dorsal margin of scaphe, with blunt tips slightly curved dorsally (Fig. 2H).

Type of tube: with thin chitinous inner lining covered in small stones cemented together.

The paratypes consist of one complete specimen, prepared for SEM, and three anterior fragments with some parts of their body wall dissected and some empty incomplete tubes.

Petta brevis sp. nov. is characterised by a cephalic veil with smooth margins, 13 pairs of paleae, 2 pairs of similar length tentacular cirri, segment 2 with pair of broad ventro-lateral lobes, each lobe with six pairs of triangular lappets, segment 3 with pair of ventro-lateral lobes, and rectangular mid ventral lobes, elongate scaphe not well separated from posterior body, lateral margin with six pairs of lobes, 9–10 pairs of blunt tipped scaphal hooks and smooth anal flap.

Petta brevis sp. nov. differs from P. pusilla Malmgren, 1866, which has the anterior margin of the cephalic veil with several lappets, in having a smooth margin to the cephalic veil, like all other species of Petta. The arrangement of lobes on segment 3 in Petta brevis sp. nov. differentiates it from P. assimilis McIntosh, 1885 and P. investigatoris Zhang, Hutchings & Kupriyanova, 2019, as these two species have lappets on the ventral lateral lobes of segment 3. The number of pairs of scaphal hooks also differs between species as well as the presence or absence of an anal cirrus: P. pusilla has 8 pairs of scaphal hooks and anal cirrus present; P. pellucida has 7 pairs of scaphal hooks and the presence/absence of anal cirrus was not stated; P. tenuis has 8 pairs of scaphal hooks and a long anal cirrus; P. investigatoris Zhang, Hutchings & Kupriyanova, 2019 and P. williamsonae Zhang, Hutchings & Kupriyanova, 2019 both have 9 pairs of scaphal hooks and long anal cirrus. For P. assimilis, no data on the number of pairs of hooks or whether an anal cirrus are present or not, was given, whereas P. brevis sp. nov. has 9 scaphal hooks on one side and 10 on the other and lacks an anal cirrus.

McIntosh described P. assimilis from Station 147 (between Prince Edward and Kerguelen Islands), 46°16'S, 48°27'E, at a depth of 1600 fathoms (= 2926 m), and recorded the sediment as being diatom ooze. His description was focussed on how similar the new species was to the British representative of the genus, which he did not actually name, and he also compared the new species with P. pusilla Malmgren, 1866, which was described from the west coast of Sweden (Zhang et al. 2019). As no other species had been described from Europe when McIntosh described his species, one must assume that he was referring to an undescribed English species. McIntosh illustrated the ventral view and the scaphal plate (McIntosh 1885, plate XLVII, figs 8, 9) and the chaetae (plate XXVIA, figs 16–19) in a schematic way but gave no information as to the number of pairs of scaphal hooks present. Branch (1994) also collected a species of Petta from a similar area but in much shallower water and identified it as P. assimilis. As noted above, we found differences between the material collected by Branch, and therefore described it as a new species. Also, the review of the genus by Zhang et al. (2019) found that all species of Petta have very restricted depth ranges, which also supports our conclusion that Petta brevis sp. nov., although collected from a similar location as P. assimilis but at a much shallower depth, should be described as new.

Hartman (1967) also recorded Petta assimilis from off Cape Horn (1806–2013 m) and the Falkland Islands, 2452 m, South America. Comparing her description with that of McIntosh (1885), it is difficult to decide if Hartman’s species is the same or yet another undescribed species of Petta. Certainly, the species recorded by Hartman differs from Petta brevis sp. nov. in terms of number of pairs of paleae and the structure of the branchiae. Although she stated that three pairs are present, the first is actually the second tentacular cirrus, and the scaphe has six pairs of triangular lobes, anal cirrus present, and 11 pairs of caudal spines that are distally slightly falcate. She mentioned that the anterior margins of segments 2 and 3 have 7 pairs of fimbriae, which on the figure (Hartman 1967, fig. 44A) equate to the ventro-lateral lobes. We suggest that the identity of Hartman’s material cannot be determined at this stage. We also regard that Petta assimilis is an indeterminate species until material from much closer to the type locality becomes available and can be examined.

This study supports the findings of Zhang et al. (2019) that species of Petta are not common and are mainly reported from the deep sea, with some species only known from type material. It must be noted that deep sea habitats are relatively poorly sampled around the world; however, because tubes of pectinariids are very conspicuous, one would expect them to be recorded if present, which reinforces our belief that this family is not well represented in the deep sea. The only exception is P. pusilla Malmgren 1866, which has been recorded from many locations at depths of 15–200 m (see Zhang et al. 2019 for a complete list); however, we suggest that these records should be checked, as its geographical range is very large with varying ecological conditions. Also, the holotype, which was examined by Zhang et al. (2019), differs from that given by Malmgren, which may have contributed to these widespread records.