Heterospio brunei, Blake & Maciolek, 2023

Blake, James A. & Maciolek, Nancy J., 2023, New species and records of Heterospio (Annelida, Longosomatidae) from continental shelf, slope and abyssal depths of the Atlantic Ocean, Pacific Ocean, Indian Ocean and adjacent seas, Zootaxa 5260 (1), pp. 1-74 : 40-44

Heterospio brunei new species

Figures 18–20

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Material examined. (12 specimens) South China Sea, off Brunei, Island of Borneo , Site CA2 , R / V Emma , coll. P.A. Neubert, Chief Scientist, BC, Sta. DA 3, 03 Jul 2011, 5.421°N, 113.492°E, 1772 m holotype ( MCZ 163717 ); Sta. DA 4, 01 Jul 2011, 5.438°N, 113.517°E, 1851 m, 2 juvs ( MCZ 163718 ); Sta. JA 1, 30 Jun 2011, 5.473°N, 113.611°E, 1888 m, 1 juv ( MCZ 163719 ); Sta. JA 3, 3 Jul 2011, 5.49°N, 113.581°E, 1922 m, 1 paratype ( MCZ 163720 ); Sta. ME 3, 26 Jun 2011, 5.343°N, 113.643°E, 1665 m, 1 paratype ( MCZ 163721 ); Sta. ME 7, 4 Jul 2011, 5.369°N, 113.624°E, 1725 m, 1 paratype ( MCZ 163722 ); Sta. ME 11, 25 Jun 2011, 5.347°N, 113.553°E, 1719 m, 1 paratype ( MCZ 163723 ); Sta. ME 14, 26 Jun 2011, 5.422°N, 113.651°E, 1792 m, 2 paratypes ( MCZ 163724 ). — Site CA1 , R / V Emma , coll. J.A. Blake, Chief Scientist, BC, Sta. 14, 06 Jun 2011, 5.757°N, 114.097°E, 1675 m, 1 paratype ( MCZ 163725 ); Sta. WH-Jokit-NE, 06 Jun 2011, 5.891°N, 114.199°E, 1400 m, 1 paratype ( MCZ 163726 ).

Description. Body long, narrow, threadlike, divided into thoracic region with setigers 1–8 crowded and setiger 9 first elongate, about two times longer than setiger 8 ( Figs. 18A , 19A ), abdominal region with elongate cylindrical segments, and posterior region terminating in bulbous pre-pygidial region bearing four setigers with hooks. No intact complete specimens, however, holotype (MCZ 163717) recognized as complete in two parts, with 23 total setigers: a 12-setiger anterior fragment and an 11-setiger posterior fragment including a 4-setiger posterior bulbous section; both fragments together 24.0 mm long, anterior setigers 0.23 mm wide, middle abdominal setigers 0.27 mm wide. Other specimens incomplete anterior fragments: 14-setiger female paratype (MCZ 163721) with eggs (147– 182 µm average diameter), 13.8 mm long, 0.26 mm wide across anterior setigers, 0.31 mm wide across abdominal setigers; 13-setiger paratype (MCZ 163724) 9.89 mm long, 0.22 mm wide across anterior setigers, 0.31 mm wide across abdominal setigers; at least three additional posterior fragments available. Color in alcohol opaque white to light tan; at least two specimens darker, likely due to retention of Rose Bengal from sample sorting procedure.

Pre-setiger region short, about as long as next 2.5 segments. Prostomium triangular, tapering anteriorly to narrow, rounded tip ( Figs. 18A–B , 19A ); eyespots absent; nuchal organs narrow slits dorsolateral on weakly swollen posterior border of prostomium ( Fig. 18A ). Peristomium in two parts; a narrow, swollen, anterior ring merged with posterior margin of prostomium and separated from a larger second ring by a groove with medial notches ( Fig. 18A ); no dorsal crest; ventrally second ring continuing across venter; mouth a wide transverse opening at posterior border of prostomium, with a row of short lobes on anterior lip and four narrow lobes on posterior lip ( Fig. 18B ); pharynx a short, rounded lobe everted on some specimens. Dorsal tentacles not observed.

Branchiae present on setigers 2–5 on all specimens except juveniles ( Figs. 18A , 19A ); most branchiae short, stubby, a few longer ones basally thick, tapering to rounded tip; prominent stubs or branchial scars typically present if long branchiae not evident; no evidence of branchiae or scars after setiger 5. Smallest juveniles with branchiae on setigers 2–3.

Thoracic region consisting of eight short setigers, each about as wide as long and a ninth transitional setiger about twice as long setiger 8 ( Figs. 18A , 19A ). All thoracic setigers slightly flattened dorsally with parapodia weakly inflated and elevated over dorsum; similarly inflated ventrally.

All parapodia biramous with setal fascicles arising from anterior edge of segment. All thoracic noto- and neuropodia of setigers 1–9 with 12–15 long capillaries in spreading fascicles arising from a rounded torus ( Fig. 18A ). Elongate abdominal setigers from setiger 10 with numerous (25+) acicular spines in both noto- and neuropodia arranged in long, transverse fascicles producing setal cinctures similar to those found on the cirratulid genus Chaetozone ( Fig. 18A ). Cinctures with about 25–30 acicular spines in each noto- and neuropodium in tight anterior row followed by numerous thin capillaries in posterior row. Cinctures with lateral and dorsal gaps between fascicles, with 50–60 spines on a side. Most spines from setiger 10 acicular with thick, weakly curved shaft tapering to narrow tip ( Figs. 18E , 19C ); a few spines in setigers 11–12 with thin arista on tip ( Fig. 18F ); posterior row all capillaries ( Figs. 18G , 19C ); aristate spines not observed in more posterior setigers. Holotype with spines on all setigers from 10–19.

Posterior bulbous section with at least four parapodia ( Figs. 18C , 19B ), each with 1–2 acicular spines in each ramus. Each spine curved, with blunt tip ( Figs. 18D , 19D ).

Methyl Green staining. Distinctive pattern on pre-setiger region and anterior thoracic setigers ( Fig. 20 ).

Remarks. With branchiae from setigers 2–5 and setiger 9 transitional, about 2–3 times longer than setiger 8, Heterospio brunei n. sp. is most similar to H. peruana (off Peru) and H. hartmanae n. sp. (North Atlantic), all from lower continental slope and abyssal depths. Both H. brunei n. sp. and H. hartmanae n. sp. have a wide transverse oral opening at the posterior border of the prostomium with a row of numerous short lobes on the anterior lip and a few larger lobes on the posterior lip; the oral morphology was not reported for H. peruana .

The main differences between these species appear to be in the nature of the spines on the abdominal parapodia and the nature of the peristomium. Heterospio brunei n. sp. has numerous simple acicular spines from setiger 10 to the end of abdominal section, the few aristate spines are limited to setigers 11 and 12. Heterospio peruana has aristate spines and subuluncini from setiger 10 but simple acicular spines are not reported; H. hartmanae n. sp. has only acicular spines, no aristate spines or subuluncini are present. All three species have two peristomial rings, but they are of very unequal size in H. brunei n. sp. with the anterior ring being very narrow and the second ring very wide, whereas they are subequal in size in H. hartmanae n. sp. and H. peruana .

Biology. Sediment grain size at all stations where Heterospio brunei n. sp. occurred contained fine sediments (97–99% silt + clay) with few sand-sized particles; total organic carbon (TOC) ranged from 0.9–3.5% at these same stations (Blake et al. unpublished data).

Etymology. The species is named for the country off which the survey was conducted.

Distribution. South China Sea, off Brunei, Island of Borneo, 1400–1922 m.

Figures

FIGURE 18. Heterospio brunei n. sp. A, anterior end (setiger 1–10), dorsal view; B, anterior end (setiger 1–4), ventral view; C, posterior end, left lateral view; D, notopodial hook from posterior end; E, neuropodial acicular spines, setiger 10; F, neuropodial aristate spine, setiger 10; G, neuropodial capillary, setiger 10. A, C–G holotype (MCZ 163717); B, paratype (MCZ 163720).

FIGURE 19. Heterospio brunei n. sp. Holotype (MCZ 163717): A, anterior end (setiger 1–10), dorsal view; B, posterior end right lateral view; C, notopodial acicular spines and capillaries, setiger 10; D, notopodial hook from posterior section. A–C stained with Shirlastain A.

FIGURE 20. Heterospio brunei n. sp. Paratype (MCZ 163720): anterior end (setiger 1–8), in left lateral view showing MG staining pattern. Arrows denote prominent MG concentrations areas on prostomium, peristomium, and anterior setigers.