Heterospio knoxi, 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 : 51-52

Heterospio knoxi new species

Figure 25

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Longosoma sp. Knox 1960: 1131 .

Material examined. Pacific Ocean, New Zealand, North Island, Hawke Bay, coll. Aug 1956, Desmond Hurley , cone grab, 39.388978°S, 177.080489°E, 13–61 m, holotype ( LACM-AHF Poly 13320); 1 paratype ( LACM-AHF Poly 13290) .

Description. A large species, both specimens incomplete, but in excellent condition. Holotype (LACM-AHF Poly 13320) with 13 setigers, 26.5 mm long, 1.4 mm wide across thoracic setiger 5; paratype (LACM-AHF Poly 13290) with 12 setigers, 19.6 mm long, 1.3 mm wide across setiger 5. Body long, narrow, divided into thoracic region with first eight setigers crowded and setiger 9 first elongate segment, as long as setigers 6–8 combined ( Fig. 25A–B ). Thoracic setigers 1–9 dorsoventrally flattened, with low mid-dorsal ridge extending from setiger 3 to 8 ( Fig. 25A ); mid-ventral ridge present from setiger 3 to anterior border of setiger 9 ( Fig. 25B ). Abdominal region with elongate cylindrical segments; posterior region not present. Color in alcohol opaque white to light tan.

Pre-setiger region short, about as long as setigers 1and 2 ( Fig. 25A–B ). Prostomium triangular, tapering anteriorly to narrow, rounded tip, posteriorly merging with anterior peristomial ring and continuing posteriorly as a carunclelike dorsal crest overlying second peristomial ring and mid-dorsum of setigers 1–2 ( Fig. 25A ); eyespots absent; nuchal organs narrow slits between posterior lateral border of prostomium and first peristomial ring. Peristomium entire ventrally, divided into two parts dorsally and laterally; these sections include a narrow, anterior ring separated from prostomium by a curved groove that includes the nuchal organs and a posterior ring separated from the first by a curved groove from which the dorsal tentacles arise ( Fig. 25A ); tentacles not present on either specimen. Ventral surface of peristomium relatively smooth; mouth a narrow vertical slit with two lateral lobes and posterior lip formed by anterior border of peristomium ( Fig. 25B ). Branchiae from setigers 2–9; thin when present; others broken or as stubs ( Fig. 25A ). Individual branchiae with short moniliform-like sections; with internal blood vessel.

All parapodia biramous with setal fascicles arising from anterior edge of segment. All thoracic noto- and neuropodia of setigers 1–9 with 40–50 long capillaries in spreading fascicles arising from a cuplike notch; neuropodia with a thickened postsetal lamella or posterior lateral flange-like enlargement on posterior side of setal fascicle ( Fig. 25B ). Elongate abdominal setigers from setiger 10 with parapodia modified into elongate ridges bearing setae that mostly encircle entire body, leaving only minute dorsal, ventral, and lateral gaps to denote individual noto- and neuropodia ( Fig. 25A–B ); when spines present, resulting armature resembles that of some cirratulid polychaetes of the genus Chaetozone . Setigers 10–11 with setae all capillaries, those of anterior row thicker and larger than those of posterior row; setiger 12 with anterior row of thicker setae, mostly subuluncini with thickened shaft and thick tapering tip, and a few acicular spines ( Fig. 25C–D ) and posterior row of slender capillaries; setiger 13 with subuluncini replaced by aristate and acicular spines in about equal numbers in anterior row ( Fig. 25E–F ) and with posterior row of thin capillaries ( Fig. 25G ).

Remarks. These two specimens of Heterospio (as Longosoma ) were donated to the late Dr. Olga Hartman during a visit by the late Dr. George Knox to the Allan Hancock Foundation in 1959; their observations on these specimens and comparison with Dr. Hartman’s H. catalinensis were reported by Knox (1960). The two specimens were originally part of a collection of 27 specimens collected in Aug 1956 from 12 stations in Hawke Bay, consisting of fine sands and muds. Coordinates given here were taken from a mid-point of the Bay since the exact station for these specimens is unknown; however, among the collections of the National Institute of Water & Atmospheric Research Ltd (NIWA), Wellington, New Zealand, nine stations are listed with specimens from this survey. These range in depth from 13 to 61 m (× = 36 ± 12.34); the data indicate that most of the 12 specimens listed have been dry and are in poor condition (G. Reid, personal communication).

Heterospio knoxi n. sp. from New Zealand, with branchiae from setigers 2–9, two peristomial rings, setiger 9 being the first elongate setiger, and aristae acicular spines in some abdominal parapodia, most closely resembles H. sinica from the East China Sea ( Wu & Chen 1966). The two species differ in that H. knoxi n. sp. has a distinct caruncle-like dorsal crest that extends from the prostomium over the peristomium to the middle of setiger 2, and both aristate and acicular spines are present in setiger 13. In contrast, H. sinica has no peristomial dorsal crest and setigers 13–17 have aristate spines but no acicular ones. See Table 1 for additional information.

Methyl Green staining. Anterior half of prostomium and branchiae not stained; stain concentrated on both peristomial rings, dorsal crest and on parapodia, best seen ventrally; rest of body staining uniformly, destaining readily.

Biology. The holotype has oocytes in the coelom measuring 145–160 µm in diameter. The habitat of Hawke Bay, New Zealand, where these specimens were collected was reported to consist of grey sands to fine muddy sands with seafloor temperatures ranging from 13.0–13.3°C ( Knox 1960) .

The report of Heterospio sp. by Estcourt (1967) from Marlborough Sound, South Island, NZ, as a dominant species in shallow subtidal benthic assemblages, may be the same as H. knoxi n. sp.

Etymology. This species is named for the late Professor George A. Knox (1919–2008), of the University of Canterbury, Christchurch, New Zealand. Professor Knox was a marine ecologist and noted authority on polychaete systematics who identified Heterospio (as Longosoma ) in New Zealand and recognized its unusual characteristics ( Knox 1960).

Distribution. New Zealand, North Island, Hawke Bay, 13– 61 m.

Figures

FIGURE 25. Heterospio knoxi n. sp. A, anterior end, dorsal view; B, anterior end, ventral view; C–D, subuluncini (C) and acicular spine (D) from setiger 12; E–G, aristate spine (E), acicular spine (F) and capillary (G) from setiger 13, A, E–F, holotype (LACM-AHF Poly 13320); B–D, paratype (LACM-AHF Poly 13290).