Heterospio antonbruunae, 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 : 56-58

Heterospio antonbruunae new species

Figure 28

urn:lsid:zoobank.org:act:EA3CFFFB-FE3B-4193-8750-A55DCAB0ADF5

Material examined. (3 specimens) Indian Ocean, Mozambique Channel between SW Africa and Madagascar, International Indian Ocean Expedition, Cruise 7, R / V Anton Bruun, Sta. 363G, 05 Aug 1964, Campbell grab, 23.633°S, 43.40°E, 1350 m, holotype ( LACM-AHF Poly 13321), 1 paratype ( LACM-AHF 13285 ); Sta. 363L, 06 Aug 1964, Campbell grab, 23.283°S, 43.50°E, 84l m, 1 paratype ( LACM-AHF Poly 13284) .

Description. All specimens incomplete, each with 11 setigerous segments. Holotype (LACM-AHF Poly 13321) 19.1 mm long and 0.26 mm wide across anterior segments; paratypes of similar lengths. Body long, thin and fragile, generally cylindrical in cross section, with distinct evidence of tearing at posterior ends; without longitudinal grooves or ridges along dorsal and ventral surfaces. Segmental boundaries denoted entirely by location of parapodia and setal fascicles. Color in alcohol opaque white; pigment entirely absent.

Pre-setiger region short, as long as first two thoracic setigers ( Fig. 28A–B ). Prostomium oval, as long as wide, distinctly rounded on anterior margin, merged with peristomium mid-dorsally ( Fig. 28B ), ventrally bordered by anterior margin of mouth; eyespots absent; nuchal organs indistinct, narrow posterior lateral grooves anterior to first peristomial ring. Peristomium divided into two rings by dorsolateral grooves from which dorsal tentacles arise in other species ( Fig. 28B ), but tentacles not present on these specimens; location of paired grooves produce prominent mid-dorsal crest between them extending to anterior margin of setiger 1 ( Fig. 28B ). Mouth located mid-ventrally between prostomium and peristomium, consisting of a large oval opening surrounded by numerous short lobes ( Fig. 28C ); pharynx observed internally on holotype or inflated externally on paratypes.

Branchiae present on setigers 2–4 ( Fig. 28A–B ); branchiae long, thin, rounded in cross section, tapering to rounded tip; branchiae with narrow ciliated groove; internal blood vessel extends along entire length.

All parapodia biramous with setal fascicles arising from near anterior border of each segment ( Fig. 28B–C ). Thoracic region of holotype and one paratype (LACM-AHF Poly 13285) with six short setigers, each slightly wider than long ( Fig. 28A–B ); segments from setiger 7 becoming progressively longer: setiger 7 first elongate setiger, about 1.5 x as long as setiger 6 ( Fig. 28A ); setiger 8 about 3.5 x as long as setiger 6 ( Fig. 28A ), followed by a very elongate setiger 9 about as long as entire anterior region from prostomium to end of setiger 8. Paratype (LACMAHF Poly 13284) with setiger 6 first elongate, about 1.5 x as long as setiger 5. All thoracic parapodia including setiger 9 with setae arising from swollen notches; postsetal lamellae not observed. Abdominal parapodia from setiger 10 with parapodia as narrow ridges or rows extending along sides of each segment, with gaps between noto- and neurosetae. Nature of more posterior parapodia unknown.

Thoracic notopodia of setigers 1–9 with numerous long capillaries in tightly packed, dense spreading fascicles, 75 or more capillaries on setigers 1–6, number of capillaries reduced on setigers 7–9; setigers 10–11 with two rows of setae, both rows with capillaries on setiger 10; setiger 11 with thin capillaries in posterior row ( Fig. 28E ) and thicker, spinous-like setae in anterior row, thick basally and tapering to fine point ( Fig. 28D ), not appearing to be either mucronate spines or subuluncini.

More posterior segments and posterior end not present.

Methyl Green staining. Narrow transverse line across venter on anterior thoracic setigers, otherwise no pattern.

Remarks. In addition to Heterospio antonbruunae n. sp. from the Mozambique Channel in 854–1350 m, three other described species have branchiae on setigers 2–4, a broadly rounded prostomium, and the first elongate setiger anterior to setiger 9: H. angolana from 105 m off West Africa ( Bochert & Zettler 2009); H. bathyala n. sp. from off the SE USA in 796–1509 m, and H. reducta , originally described from lower slope depths of 2335 m in the Mediterranean by Laubier et al. (1974) and variously reported from shallower bathyal depths off Ireland ( Amoureux 1982; this study) and Iceland ( Parapar et al. 2014). Of these four, H. angolana is the only one from shallow shelf depths and differs from the other three in having a single peristomial ring instead of two. Of the three deep-water species, H. antonbruunae n. sp. is most similar to H. bathyala n. sp. in having a broadly rounded prostomium and branchiae from setigers 2–4. The two species differ in that setiger 6 or 7 is the first elongate setiger in H. antonbruunae n. sp. instead of setiger 8 and the mouth opening of H. bathyala n. sp. has only 4–6 large lobes surrounding the mouth instead of many small ones. There are also acicular spines on setigers 12–14 of H. bathyala n. sp., however, these setigers are not yet known for H. antonbruunae n. sp. See Table 1 for further comparative observations.

Etymology. This species is named for the R/V Anton Bruun, the primary research vessel for the International Indian Ocean Expedition surveys of 1963–1965.

Distribution. Continental slope off Madagascar, Mozambique Channel, 854–1350 m.

Figures

FIGURE 28. Heterospio antonbruunae n. sp. A, diagram of first nine setigers of holotype, dorsal view; B, first seven setigers of holotype, dorsal view; C, first four setigers of holotype, ventral view; D, three large neuropodial spinous-like capillaries from anterior row of setiger 11; E, thin neuropodial capillary from second row of setiger 11. A–B. holotype (LACM-AHF Poly 13321); C–E, paratype (LACM-AHF Poly 13285).