Heterospio bathyala, 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 : 16-20

Heterospio bathyala new species

Figures 5–6

urn:lsid:zoobank.org:act:8CFC9701-A0C8-4E39-8ED7-85A67D30E7D4

Heterospio cf. longissima: Blake et al. 1987 ; Blake & Grassle 1994: 861; Hilbig 1994: 941 (in part). Not Ehlers 1874, 1875; Hartman 1965.

Material examined. (27 specimens) Southeastern United States, U.S. South Atlantic ACSAR Program , off Cape Fear , North Carolina, coll. J.A. Blake. Sta. 11, Cruise SA-4, Rep. 1, 22 May 1985, BC, 33.081°N, 76.418°W, 800 m, holotype ( USNM 1673076 ) , 2 juvs ( USNM 1673077 ) ; Rep. 3, 22 May 1985, BC, 33.81°N, 76.423°W, 799 m, 1 juv ( USNM 1673078 ) ; Cruise SA-5, Rep. 1, 23 Sep 1985, BC, 33.081°N, 76.42°W, 796 m, 1 paratype ( USNM 1673079 ) ; Rep. 2, 23 May 1985, BC, 33.081°N, 76.2517°W 796 m, 2 paratypes ( USNM 1673080 ) ; Rep. 3, 23 May 1985, BC, 33.081°N, 76.419°W, 797 m, 2 paratypes ( USNM 1673081 ) ; Cruise SA-6, Rep. 2, 22 Nov 1985, BC, 33.083°N, 76.419°W, 804 m, 3 paratypes ( USNM 1673082 ) ; Sta. 14, Cruise SA-4, Rep. 1, 20 May 1985, BC, 33.394°N, 77.019°W, 805 m (4, USNM 1673083 ) ; Rep. 2, 20 May 1985, BC, 33.394°N, 77.02°W, 802 m (3, USNM 1673084 ) ; Rep. 3, 20 May 1985, BC, 33.395°N, 77.019°W, 803 m (3, USNM 1673085 ) ; Cruise SA-5, Rep. 1, 19 Sep 1985, BC, 33.395°N, 77.02° W, 796 m, 1 paratype ( USNM 1673086 ) ; Rep. 2, 19 Sep 1985, BC, 33.395°N, 77.021°W, 799 m, 1 juv ( USNM 1673087 ) ; Cruise SA-6, Rep 1, 18 Nov 1985, BC, 33.396°N, 77.018°W, 799 m, 3 paratypes ( USNM 1673088 ) ; Rep. 3, 18 Nov 1985, BC, 33.395°N, 77.018°W, 799 m (3, USNM 1673089 ) .— Off Cape Lookout, North Carolina. Sta. 3, Cruise SA-3, 14 Jul 1984, BC, 34.242°N, 75.672°W, 1509 m (1, USNM 1673090 ) .

Description. All specimens incomplete. Body long, narrow, threadlike; available anterior fragments with 11–14 setigerous segments, divided into thoracic region with 1–7 crowded setigers and setiger 8 as the first elongated segment; these followed 3–6 elongate cylindrical abdominal segments ( Figs. 5A , 6A ). Most specimens with a total of 11–12 setigerous segments. One posterior fragment terminating in bulbous pre-pygidial region bearing hooked spines ( Fig. 6F ). Holotype (USNM 1673076) anterior fragment with 12 setigers, 16.5 mm long and 0.23 mm across thoracic segments ( Fig. 5A, C ); paratype (USNM 1673081) with 12 setigers, 16.7 mm long, 0.28 mm wide; paratype (USNM 1673082) with 13 setigers, 14.25 mm long, 2.7 mm wide. A few mid-body fragments suggest at least 14- setiger specimens collected, but not intact. Juvenile (USNM 1673086) anterior fragment with 11 setigers, 3.1 mm long and 0.1 mm wide. Color in alcohol opaque white to light tan; pigment entirely absent.

Pre-setiger region short, only as long as first 1.5 thoracic setigers ( Figs. 5A–D , Fig. 6B ). Prostomium flattened, disk-like, broadly rounded anteriorly ( Fig. 5A–C ), with middle of dorsal surface becoming elevated as broad crest extending over peristomium and merging with setiger 1 ( Figs. 5A–B, D , 6B ), eyespots absent; nuchal organs narrow posterior lateral grooves anterior to first peristomial ring ( Fig. 6B ). Peristomium with narrow anterior ring separated from large posterior ring by dorsolateral grooves from which dorsal tentacles arise ( Figs. 5B, D , 6E ); these located laterally; when present, tentacles elongate thickened filaments ( Fig. 6A, E ); peristomium interrupted by middorsal crest; ventral surface relatively smooth; mouth located mid-ventrally between prostomium and peristomium, consisting of 4–6 short lobes surrounding oral opening ( Fig. 5C ).

Branchiae or their stubs present on setigers 2–4 on all specimens examined except juveniles ( Figs. 5A–B , 6A– C, E ); most branchiae long, thin, rounded in cross section, tapering to rounded tip; branchiae with narrow ciliated groove; internal blood vessel extends along entire length ( Fig. 6B, E ). Juveniles with branchiae observed only on setiger 2.

All parapodia biramous with setal fascicles arising from near anterior edge of segment. Thoracic region of all specimens including juveniles with seven short setigers, each slightly wider than long; with setiger 8 being first elongate setiger ( Fig. 5A ), about as long as setigers 1–6, shorter in juveniles; setiger 9 very elongate, about 20x longer than setigers 1–7; setigers 10–12 or 13 each 25–30x longer than thoracic setigers. All thoracic setigers slightly flattened dorsally with parapodia weakly inflated and elevated over dorsum. Abdominal setigers similarly inflated ventrally; abdominal setigers round in cross section. Abdominal parapodia from setiger 10 with parapodia as narrow elongate lobes, becoming thicker and more prominent from setigers 11–12; noto- and neuropodia with distinct dorsal and ventral gaps; lateral gaps between noto- and neuropodia narrower.

All thoracic notopodia of setigers1–8 with 12–16 long capillaries in spreading fascicles; capillaries of neuropodia more numerous with 25–30 setae arranged in tight, dense fascicle. Noto- and neuropodia of setigers 9–11 with capillaries in two short transverse rows with wide dorsal and ventral gaps and narrow lateral gaps between noto- and neuropodia; setiger 12 with capillaries ( Fig. 5E ) and usually a few acicular spines ( Fig. 5F ) and rarely an aristate spine or thickened capillary in anterior row; setigers 13–14 with numerous acicular spines in anterior row and narrow capillaries in posterior row; aristate spines present or absent. Spines and capillaries of noto- and neuropodia from setiger 13 in longer cinctures, each with 10–12 acicular spines in anterior row and about 25 or more capillaries in posterior row or about 20–24 acicular spines from noto- and neuropodia on a side. Spines flattened, tapering to narrow pointed tip ( Fig. 5F ), some with a very short aristate tip. Far posterior bulbous section with two parapodia, each bearing 1–2 hooked spines in each ramus. Each spine short, pointed, with curved tip ( Fig. 5G ).

Segments of elongate abdominal region with transverse muscle bands; these believed to support stretching of elongate segments ( Blake & Maciolek 2019); continuing until posterior bulbous section. Posterior bulbous section oval-shaped, with terminal anal opening ( Fig. 6F ).

Methyl Green staining. Stain concentrates on peristomium and a few anterior thoracic setigers ( Fig. 6C ); prostomium not stained; abdominal setigers with stain retained laterally in bands anterior to parapodia and variably along individual segments as irregular speckles ( Fig. 6C–D ).

Remarks. Heterospio bathyala n. sp. is most similar to H. reducta Laubier, Picard & Ramos, 1974 originally reported from deep water (2335 m) in the Mediterranean Sea north of Algeria and H. angolana Bochert & Zettler, 2009 from shelf depths (105–146 m) off Angola, West Africa. All three species have a reduced number of branchiae (three pairs) and the first elongated segment is setiger 8. Heterospio reducta is reported to have only capillary setae in posterior cinctures; however, no specimens with more than 12 setigers have been reported ( Laubier et al. 1974; Borowski 1994; Parapar et al. 2014; this study).

Heterospio angolana is therefore the species most similar morphologically to H. bathyala n. sp. The two species differ in that H. bathyala n. sp. has a broadly rounded, flattened, disk-like prostomium followed by a raised dorsal crest that extends posteriorly over the peristomium and onto setiger 1; in contrast, the prostomium of H. angolana is conical, narrowing to a rounded tip, and has no dorsal crest. In addition, H. angolana is described as having numerous aristate spines or subuluncini in the anterior setal row from setiger 12 and a posterior row of numerous simple acicular spines. In contrast, H. bathyala n. sp. has an anterior row of simple pointed acicular spines and a posterior row of simple capillaries. A few aristate spines may be present with acicular spines on setiger 12, but are not present on setigers 13–14.

Biology. Heterospio bathyala n. sp., although rare, was concentrated at Stations 11 (off Cape Fear, NC) and 14 (off Charleston, NC) along the 800-m isobath, with only a single specimen collected elsewhere in survey areas off the Carolinas. Station 14, with 436 species of benthic invertebrates collected from nine box core samples (0.81 m 2) over three surveys, had the highest species richness and diversity for any site during the entire U.S. ACSAR program sampled from the Canadian boundary to off the Carolinas ( Blake et al. 1987; Blake & Grassle 1994). The dominant polychaete at both stations was Microrbinia linea Hartman, 1965 , a small threadlike orbiniid that is widespread along the entire U.S. Atlantic continental slope ( Blake 2021a).

Stations 11 and 14 were adjacent sites in areas influenced by the Gulf Stream and complex local bottom currents ( Blake & Grassle 1994); both sites were thought to be depositional and had similar sediments that were well mixed with a water content of about 57%. The nine sediment samples each at Stations 11 and 14 averaged over all three surveys included the following results for percent sand, silt and clay fractions ( Blake et al. 1987): Station 11: sand (39 ± 3), silt (33.9 ± 2.5), clay (26.9 ± 1.8); Sta. 14: sand (41 ± 0.7); silt (33.1 ± 1.5); clay (25.87 ± 2.3). Station 14 is in an area of high productivity and sedimentation with an average mean percent total carbon in the sediments of 3.67 ± 0.67.

Etymology. The epithet is derived from the Greek, bathys, for deep, denoting the bathyal depths from which this species was collected.

Distribution. U.S. continental slope off North Carolina; off Charleston, SC, and Cape Fear, NC, 796–804 m; off Cape Lookout, NC, 1509 m.

Figures

FIGURE 5. Heterospio bathyala n. sp. A, anterior 10 setigers, dorsal view; B, anterior end, dorsal view; C, anterior end, ventral view; D, anterior end, right lateral view; E, capillary notoseta setiger 12; F, acicular spine, setiger 12; G, hook from posterior end. A, C, E, F, holotype (USNM 1673077); B, D, paratype (USNM 1633079); G, (USNM 1673085).

FIGURE 6. Heterospio bathyala n. sp. A, 13-setiger anterior fragment with dorsal tentacle attached; B, anterior end, left lateral view; C, anterior end, right lateral view; D, same, middle segments; E, anterior end, left lateral view with dorsal tentacle attached; F, bulbous posterior end, right lateral view. A–B paratype (USNM 1673082); C–D, paratype (USNM 1673080); E, paratype (USNM 1673081); F, (USNM 1673085). A–B, E stained with Shirlastain A; C–D stained with MG. C–D, arrows denote concentrations of MG.