Leitoscoloplos sahlingi, Blake, 2020

Blake, James A., 2020, New species and records of deep-water Orbiniidae (Annelida, Polychaeta) from the Eastern Pacific continental slope, abyssal Pacific Ocean, and the South China Sea, Zootaxa 4730 (1), pp. 1-61 : 15-17

Leitoscoloplos sahlingi new species

Figure 7

urn:lsid:zoobank.org:act:1ABF6485-9B70-43D1-A421-215DD4A2A35C

Material examined. Continental margin off Oregon, Cascadia Subduction Zone, southern summit of Hydrate Ridge , R / V Sonne Cruise 143, coll. H. Sahling, Sta. 179, 17 Aug 1999, 44°34.2′N, 125°08.8′W, 786 m, holotype ( MCZ 153567 ) and 2 paratypes ( MCZ 153568 ) .

Description. A small species, all specimens incomplete. Holotype 6.8 mm long, 0.67 mm across thorax, with 37 setigers; large paratype 5.5 mm long, 0.87 mm wide across thorax, with 30 setigers. Bodies relatively thick, robust in thoracic region with smooth crowded segments, each about four times wider than long ( Fig. 7A ); abdominal segments becoming narrower and shorter. Dorsum of thorax rounded dorsally, venter flattened mid-ventrally; abdominal region flattened dorsally, rounded ventrally. Thoracic segments all uniannulate; abdominal segments becoming biannulate due to parapodial ridge elevated above rest of segment. Color in alcohol: light tan.

Pre-setiger region about as long as first two setigers. Prostomium triangular, narrowing to pointed apex ( Fig. 7 A–B); eyespots absent; nuchal organs prominent oval grooves on border with peristomium ( Fig. 7B ). Peristomium composed of one achaetous ring extending ventrally, surrounding mouth ( Fig. 7 A–B). Thorax with 12 setigers, abruptly separated from abdominal segments by loss of most neurosetae and increased size and shape of neuropodial lobe on setiger 13 ( Fig. 7A ).

Thoracic notopodial and neuropodial lamellae elongate, digitiform, arising from broad base ( Fig. 7C ), both similar in form; abdominal notopodia of anterior abdominal segments becoming long and narrow ( Fig. 7D ). Abdominal neuropodia thickened, divided into a rounded terminal lobe and short laterally directed ventral cirrus ( Fig. 7D ). Branchiae first present from setiger 10 ( Fig. 7A ), short at first then increasing in size; branchiae of middle abdominal segments long, triangular, and flattened, tapering to narrow papilla ( Fig. 7D ), each branchia about onethird longer than notopodial lamellae.

All setae camerated capillaries except neuropodial aciculae; furcate and flail setae absent. Thoracic noto- and neurosetae with numerous capillaries organized in separate rows: 2–4 rows of notosetae and 4–5 rows of neurosetae. Abdominal notosetae include 7–8 capillaries, some long; abdominal neurosetae include 4–5 capillaries and 1–2 short protruding pointed aciculae, these minute.

Pygidium not observed.

Methyl Green stain. No pattern, prostomium not staining, body staining uniformly, de-stains rapidly.

Remarks. Leitoscoloplos sahlingi n. sp. belongs to a group of species having branchiae first present from middle to posterior thoracic segments ( Blake 2017). Four other species in this category occur in the eastern Pacific: L. mexicanus , L. multipapillatus Hernández-Alcántara & Solís-Weiss, 2014 , L. panamensis ( Monro, 1933) , and L. pugettensis . Of these, L. multipapillatus and L. panamensis differ from L. sahlingi n. sp. in having instead of lacking subpodial lobes or stomach papillae across the venter of some thoracic segments. Leitoscoloplos pugettensis is the most common shallow-water orbiniid species in the eastern Pacific. This species differs from L. sahlingi n. sp. in having 14–20 thoracic setigers instead of 12, and branchiae from setigers 13–18, instead of 10. More importantly L. pugettensis has furcate setae in abdominal notopodia that are absent in L. sahlingi n. sp.

The remaining species, L. mexicanus , is the only deep-water species in the group and the most similar to L. sahlingi n. sp. Specimens reported by Fauchald (1972) from soft sediments in the Salsipuedes Basin, Gulf of California ( Mexico) in 1377–1418 m are incomplete and similar in size (5.5 mm long, with 29 setigers) to those of L. sahlingi n. sp., which are also incomplete (6.8 mm long, with 37 setigers). Both species lack furcate setae. However, L. mexicanus has 13–14 thoracic setigers instead of 12 and branchiae from setiger 11–13 instead of 10. The morphol- ogy of the abdominal segments of L. mexicanus differs from that of L. sahlingi n. sp. as follows: (1) the branchiae are narrow along their length instead of triangular and tapering to a terminal papilla; (2) the notopodial lamella is inflated along its length instead of tapering to a pointed tip; and (3) the neuropodium bifurcates into two subequal lobes instead of a dorsal rounded lobe and a short ventral cirrus.

Etymology. This species is named for the late Dr. Heiko Sahling (1969–2018), marine ecologist, who collected and provided these specimens of Leitoscoloplos and other polychaetes from the Cascadia Subduction Zone and authored an important paper on the macrofauna of the site ( Sahling et al. 2002).

Distribution. Sediments with gas hydrates, off Oregon, Cascadia Subduction Zone, 786 m.

Figures

FIGURE 7. Leitoscoloplos sahlingi n. sp. Holotype (MCZ 153567): A, anterior end, dorsal view. Paratype (MCZ 1563568): B, anterior end, left lateral view; C, thoracic setiger, anterior view; D, middle abdominal setiger, posterior view.