Heterospio hartmanae Blake & Maciolek 2023, new species

Heterospio hartmanae new species

Figures 2–3

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Heterospio longissima: Hartman 1965: 163–164, Plate 30, figs. F–H; Hartman & Fauchald 1971: 108–109 (in part). Not Ehlers 1874, 1875.

Heterospio cf. longissima: Blake & Grassle 1994: 861 (in part); Hilbig 1994: 941 (in part). Not Ehlers 1874, 1875.

Not H. longissima sensu Hartman: Laubier et al. 1974; Borowski 1994; Parapar et al. 2014, 2016.

Material examined. (55 specimens in addition to many middle and posterior fragments) Western North Atlantic Ocean. Off New England, Gay Head Bermuda Transect, coll. H. L. Sanders and R.R Hessler. R/V Atlantis Cruise 264, Sta. II-2, 24 May 1961, AD, 38.083°N, 69.6W, 3752 m, holotype (LACM-AHF Poly 13270); 4 paratypes and post. ends, (LACM-AHF Poly 13271); Sta. HH-3, 21 May 1961, AD, 38.783°N, 70.133°W, 2900 m (3, small, LACM-AHF Poly 13272); Sta. II-1, 22 May 1961, AD, 37.983N, 69.533W, 3742 m, 1 paratype and 2 post. ends (LACM-AHF Poly 13273); R/V Atlantis Cruise 273, Sta. JJ-1, 02 Oct 1961, AD, 37.45°N, 68.683W, 4436 m (4, dry, LACM-AHF Poly 13274); Sta. GH-4, 03 Oct 1961, AD, 39.8°N, 70.95W, 2470 m (1, small, LACM-AHF Poly 13275); R/V Atlantis Cruise 277, Sta. JJ-3, 25 May 1962, AD, 37.217°N, 68.66°W, 4540 m (1, LACM-AHF Poly 13276); Sta. NN-1, 29 May 1962, AD, 33.942°N, 66.567°W, 4950 m (1 juv, LACM-AHF Poly 13277); R/V Atlantis II Cruise 12, Sta. 65, AD, 21 Aug 1964, 38.78°N, 70.113°W, 2891 m (3 post. ends, LACM-AHF Poly 13278); Sta. 71, 24 Aug 1964, AD, 38.133°N, 71.792°W, 2946 m, 10 paratypes and 9 post. ends and fragments., (LACM-AHF Poly 13279); Sta. 72, 24 Aug 1965, EBS, 38.267°N, 71.783°W, 2864 m (1, ant., LACM-AHF Poly 13280); R/V Chain, Cruise 50, Sta. Ch- 85, 05 Jul 1965, EBS, 37.987°N, 69.437W, 3834 m (2, LACM-AHF Poly 13281); R/V Atlantis II, Cruise 17, Sta. 95, EBS, 17 Dec 1965, 38.55°N, 68.533°W, 3573 m, 11 paratypes, 3 post. ends (LACM-AHF Poly 13282). — Off New Jersey and Delaware, U.S. Mid-Atlantic ACSAR Program, coll. R. Petrecca, Chief Scientist. Sta. 12, Cruise Mid-1, Rep. 2, 07 May 1984, BC, 38.489°N, 72.704°W, 2501 m, (1, USNM 1673091); Rep. 3, 07 May 1984, BC, 38.489°N, 72.704°W, 2500 m (1 juv, USNM 1673092). — Off Cape Fear, North Carolina, U.S. South Atlantic ACSAR Program, coll. J.A. Blake, Chief Scientist. Sta. 13, Cruise SA-4, Rep. 1, 21 May 1985, BC, 32.92°N, 73.83°W, 3015 m (1 post. end, USNM 1673093); Cruise SA-5, Rep. 1, 21 Sep 1985, BC, 32.921°N, 75.833°W, 3006 m (2, USNM 1673094); Rep. 2, 21 Sep 1985, BC, 32.919°N, 75.831° W, 3009 m (1, USNM 1673095); Cruise SA-6, Rep. 2, 20 Nov 1985, BC, 32.92°N, 75.837°W, 3002 m (1, USNM 1673096); Rep. 3, 21 Nov 1985, BC, 32.921°N, 75.835°W, 3006 m (1, USNM 1673097). — Off Charleston, South Carolina, coll. J.A. Blake, Chief Scientist. Sta. 16, Cruise SA-5, Rep. 1, 14 Sep 1985, 31.587°N, 75.173°W, 3009 m (1, USNM 1673098); Rep. 2, 16 Sep 1985, BC, 31.586′N, 75.171°W, 3011 m (2, USNM 1673099); Cruise SA-6, Rep. 2, BC, 20 Nov 1985, 31.585°N, 75.172°W, 3009 m (1, USNM 1673100); Rep. 3, 20 Nov 1985, BC, 31.586°N, 75.17° W, 3012 m (1, USNM 1673101).

Description. Body long, narrow, threadlike (Fig. 2A–C), divided into an anterior thoracic region with crowded, slightly flattened segments, abdominal region with elongate cylindrical segments, and posterior region terminating in a bulbous pre-pygidial region bearing hooked spines. All larger specimens fragmented: largest holotype (LACM AHF-Poly 13270) with 13 setigers, 14.1 mm long, 0.4 mm wide across anterior setigers; paratype (LACM AHFPoly 13273) with 12 setigers, 14.9 mm long, 0.2 mm wide across anterior setigers. Only complete specimen (USNM 1673091) smaller, slender, with nine thoracic setigers, 15 abdominal setigers, and three setigers in posterior bulbous section for a total of 27 setigerous segments, this specimen 9.45 mm long, and 0.11 mm wide across thoracic segments (Fig. 2A–C). Color in alcohol opaque white to light tan; pigment entirely absent.

Pre-setiger region short, about as long as first 3 or 3.5 thoracic segments (Figs. 2D–E; 3A–C). Prostomium roughly rhomboid-shaped, tapering anteriorly from wide middle section to narrow, rounded tip; posteriorly narrowing, encompassed by first peristomial ring (Figs. 2D–E, 3A–C); eyespots absent; nuchal organs narrow slits on posterior lateral margins (Fig. 3A). Peristomium with two rings, both prominent dorsally and laterally; first ring surrounding prostomium dorsally like a yoke, continuing laterally but not onto ventral surface; second ring a large achaetous segment interrupted dorsally by posterior extension of prostomium and complete ventrally, encompassing mouth (Fig. 3A–C). Mouth a transverse opening with anterior lip formed by 7–8 short lobes and posteriorly by 3–4 narrow lobes (Fig. 3B); pharynx everted on some specimens, short, rounded sac-like. A single dorsal tentacle observed on right side of one small specimen (USNM 1673098); this tentacle long, thickened in middle, arising from groove between anterior and posterior peristomial rings, subsequently detached during examination.

Branchiae present on setigers 2–5 (Fig. 3A, C) on all specimens examined except juveniles; most branchiae short, stubby, a few longer ones basally thick, tapering to rounded tip; prominent stubs or branchial scars typically present if individual 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 2.5 times longer than setiger 8 (Figs. 2D–E, 3A–C). All thoracic setigers slightly flattened dorsally with parapodia weakly inflated and elevated over dorsum; similarly inflated ventrally.Abdominal setigers elongated from setiger 10, about 20–25 times longer than short thoracic setigers; setigers 10–24 elongate on complete specimen (USNM 1673091) and 10–14 on larger anterior fragments.

All parapodia biramous with setal fascicles arising from anterior edge of segment, lateral and dorsal gaps between setal fascicles defining noto- and neuropodia. All thoracic noto- and neuropodia of setigers 1–9 with 12–15 long capillaries in spreading fascicles; abdominal setae from setiger 10 arranged in two rows producing cirratulidlike cinctures with numerous (25+) acicular spines in both noto- and neuropodia on each side, thus 50–60 spines on each side or 100–120 per segment; spines in anterior row accompanied by 25–30 or more thin capillaries in posterior row. Abdominal acicular spines with thick, weakly curved shaft tapering to narrow tip (Figs. 2F–G, 3F); aristate setae not present. Spines present on all abdominal setigers except last 3–4 posterior segments where setae all capillaries; complete 27-setiger specimen (USNM 1673091) with spines absent on setigers 22–24.

Far posterior bulbous section with at least 2–3 parapodia each bearing two distinctly separated acicular spines in each ramus (Fig. 3D). Each spine yellow, curved, with blunt tip (Figs. 2C [inset], 3E).

Methyl Green staining. Prostomium and peristomium stain intensely; segmental bands most evident ventrally.

Remarks. The description of Heterospio hartmanae n. sp. presented here is based on the original materials collected from off New England to Bermuda by the late Drs. H.L. Sanders and R.R. Hessler and identified and reported as H. longissima Ehlers, 1874 by Hartman (1965) and Hartman & Fauchald (1971). A few additional specimens collected as part the U.S. ACSAR program off the Carolinas and off Delaware and New Jersey are also included. The species occurs in lower continental slope and abyssal depths from about 2500–4950 m.

As detailed above in the previous section on Heterospio longissima, Hartman’s (1965) version, which has been followed by recent investigators as representative of the type-species, has been found to differ from the original description by Ehlers (1874, 1875) and is also an incorrect description of the materials themselves. Major differences between Hartman’s (1965) account and the present examination of the same specimens include the distribution of branchiae (setigers 1–9 vs. 2–5), the shape of the prostomium (narrow and pointed vs. conical and rounded), the presence or absence of thick palps, and the origin of the setae from middle of segments vs. from the anterior margin.

With the morphological differences reported here, the placement of the species among the known species of Heterospio changes. Rather than H. longissima, the species most similar to H. hartmanae n. sp. are H. peruana Borowski, 1994, an abyssal species from off western South America, and H. brunei n. sp. from deep-water in the South China Sea (see below). All three species have branchiae limited to setigers 2–5, a 9-setiger thoracic region of which the first eight are short and a transitional ninth that is about 2.5 times longer than each of the first eight setigers; all nine thoracic setigers have capillary setae. The first setal cinctures occur on setiger 10, which is the first abdominal setiger. While the shape of the thick curved spines on the posterior bulbous section appears to be the same in all three species, the acicular spines in the abdominal setigers are different. In H. hartmanae n. sp. the abdominal spines in the cinctured segments are mainly simple spines with narrow rounded tips; only a few have pointed tips and none are aristate. In contrast, the acicular spines of cinctured segments in H. peruana are illustrated by Borowski (1993) as distinctly aristate or subuluncinate-like capillaries where the extended tip is thicker than the smoothly tapering tip of typical capillaries. Heterospio brunei n. sp. has a few aristate spines in the first one or two abdominal setigers, but most are acicular throughout. More importantly, H. hartmanae n. sp. has two prominent peristomial rings, whereas H. brunei n. sp. has only one.

Biology. Sediment grain size data are available for the two abyssal stations off the Carolinas where Heterospio hartmanae n. sp. was collected (Blake et al. 1987; Blake & Grassle 1994). Station 13 off Cape Fear, NC, and Station 16 off Charleston, SC, were adjacent sites along the 3000 m isobath and had similar sediment characteristics; both sites had high silt + clay fractions and a water content of about 56.3%. The nine sediment samples collected at each of station, averaged over all three surveys, included the following results for percent sand, silt and clay fractions: Sta. 13: sand (17.6 ± 5.1); silt (38.8 ± 4.1); clay (43.5 ± 3.7); Sta. 16: sand (6.0 ± 1.1); silt (38.3 ± 1.1); clay (52.4 ± 1.6).

Blake & Grassle (1994) reported that the polychaetes Microrbinia linea Hartman, 1965, Prionospio sp. 2, and Myriochele sp. 1 were the three most abundant species at Sta. 13 and M. linea, Prionospio sp. 2, and Siboglinum sp. 2 were the three most abundant species at Sta. 16. Heterospio hartmanae n. sp. ranked 14 th at Sta. 16.

Etymology. This species is named after the late Dr. Olga Hartman, who recognized the unusual nature of Heterospio. Dr. Hartman’s lifetime of work on polychaete systematics has been an inspiration to the present authors and polychaete researchers worldwide.

Distribution. Lower continental slope and abyssal depths of the Western North Atlantic Ocean, off eastern North America, 2470–4950 m.