Heterospio southwardorum Blake & Maciolek 2023, new species
Creators: name: Blake, James A.
name: Maciolek, Nancy J.
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Annelida
Polychaeta
Spionida
Longosomatidae
Heterospio
Heterospio southwardorum

description: Heterospio southwardorum new species   
Figure 12  
urn:lsid:zoobank.org:act: A65BA064-DF88-44FC-A223-A47C4CDABCC9  
 Material examined. NE Atlantic Ocean, Bay of Biscay, off Bilbao, Spain, R / V Sarsia, Cruise 5, Sta. 5-56, 19 Jul 1967, coll. A. & E. Southward, EBS, 43.717°N, 03.797°W, 641 m, holotype ( LACM-AHF 13283).   
 Description. A moderately sized species, holotype ( LACM-AHF 13283) incomplete with 13 setigers, 21.3 mm long, 0.43 mm wide across thoracic segments, 0.37 mm wide across middle abdominal segment. Thorax with eight crowded segments followed by elongate setiger 9. Setigers 1–7 twice as wide as long; setiger 8 slightly longer, about as wide as long; setiger 9 greatly elongated, as long as setigers 1–8 combined. Abdominal setigers 10–13 long, narrow, encompassing about 16 mm of total length of holotype. Color in alcohol opaque white to light tan; pigment entirely absent.   
Pre-setiger region short, as long as first two thoracic setigers (Fig. 12A–B). Prostomium flattened, disklike, broadly rounded anteriorly (Fig. 12A–B); eyespots absent; nuchal organs elongate slits anterior to anterior peristomial ring (Fig. 12A). Peristomium with two rings; first ring narrow, dorsally visible posterior to nuchal organs, not continuing ventrally; second ring large, similar in size and shape to following setigers, interrupted by broad dorsal crest that merges with setiger 1 (Fig. 12A), entire on ventral surface, interrupted by mouth (Fig. 12B). Dorsal tentacles not present, but scars evident in notch between peristomial rings. Mouth a triangular-shaped opening surrounded laterally by thickened lobes (Fig. 12B); proboscis not everted.  
Branchiae or their stubs present on setigers 2–7 (Fig. 12A); intact branchiae short, oval-shaped. All parapodia biramous with setal fascicles arising from near anterior edge of segment. Thoracic region with eight short setigers (Fig. 12A), each slightly wider than long; setiger 8 slightly longer than those preceding. Setiger 9 elongated, as long as setigers 1–8 combined. All thoracic setigers slightly flattened dorsally with notopodia of setigers 1–7 weakly inflated and elevated over dorsum; notopodia of setigers 8–9 with thickened lobes from which setae arise; neuropodia of setigers 1–9 with short, postsetal lobes (Fig. 12B), most evident on setigers 1–7. Abdominal segments from setiger 10 rounded in cross section with parapodia on anterior borders as transverse ridge encircling body, producing cinctures or rows of setae similar to those of some cirratulids; these ridges interrupted dorsally, ventrally, and laterally denoting location of noto- and neuropodia.  
All thoracic notopodia of setigers1–9 with 12–16 long capillaries in spreading fascicles; capillaries of neuropodia more numerous, with 25–30 arranged in tight, dense fascicle. Setae of noto- and neuropodia of following setigers in two transverse rows; setigers 10–11 all capillaries, rows with distinct dorsal and lateral gaps; setiger 12 with all capillaries in notopodia and a few acicular spines in anterior row of neuropodia; setiger 13 with cinctures of 10–12 spines in anterior row and 25–30 capillaries (Fig. 12C) in posterior row; capillaries with thin fine tip; spines flattened, tapering to narrow pointed tip, none with aristate tip (Fig. 12D).  
Posterior bulbous section not present.  
 Methyl Green staining. No pattern, stain not concentrated anywhere along body.   
 Remarks. Heterospio southwardorum n. sp. is most similar to H. mediterranea. Both species have a broad disklike prostomium, two peristomial rings, dorsal peristomial crest, and in both species setiger 9 is the first elongate segment, being as long as setigers 1–8 combined. The two species differ in that in H. southwardorum n. sp. the first peristomial ring is narrow and separated from the prostomium by the nuchal groove, branchiae are present on setigers 2–7, capillary setae are present on setigers 10–11, with acicular spines first present on setigers 12–13, and subuluncini are absent. In contrast, H. mediterranea has both peristomial rings of an equivalent size, branchiae are present on setigers 2–8, and capillary setae are present on setigers 10–12, with acicular spines and subuluncini first present from setiger 13. See Table 1 for further comparison of H. southwardorum n. sp. with its congeners.   
 Etymology. This species is named for the late Drs. Alan and Eve Southward, prominent marine zoologists who directed the R/V Sarsia cruise in the Bay of Biscay during which this species was collected. Dr. Eve Southward was a deep-sea biologist and an authority on annelids of the family Siboglinidae.   
 Distribution. North Atlantic Ocean, Bay of Biscay off Spain, 641 m.
description: Published as part of 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, pp. 1-74 in Zootaxa 5260 (1) on pages 30-32, DOI: 10.11646/zootaxa.5260.1.1, http://zenodo.org/record/7794920