Heterospio guiana, 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 : 27-30

Heterospio guiana new species

Figures 10–11

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Heterospio longissima: Hartman 1965: 163–164 (in part). Not Ehlers 1874, 1875.

Material examined. (10 specimens) Off Suriname (Dutch Guiana), coll. H.L. Sanders & R. R. Hessler, R / V Chain, Cruise 35, Sta. DR 33, 25 Apr 1963, AD, 07.867°N, 54.525°W to 07.917°N, 54.583°W, 520–550 m, holotype ( LACM-AHF Poly 13268) and 9 paratypes ( LACM-AHF Poly 13269) .

Description. All specimens incomplete. Holotype (LACM-AHF Poly 13268) an anterior fragment with 11 setigers, 7.34 mm long and 0.50 mm across thoracic segments; 10-setiger paratype 7.12 mm long, 0.65 mm wide ( Figs. 10B , 11A ); 11-setiger paratype 7.54 mm long, 0.35 mm wide. Juvenile anterior fragment with 11 setigers, 3.1 mm long and 0.1 mm wide. Body long, narrow, threadlike; available anterior fragments divided into thoracic region of nine setigers, with first eight crowded, followed by setiger 9, a longer transitional segment about three times length of setiger 8 ( Figs. 10A , 11A–B ). Transition from thoracic segments with defined dorso-lateral setal fascicles to abdominal segments at setiger 10 denoted by entirely different setal arrangement with setae arising from broad cincture-like fascicles with rows of setae mostly surrounding anterior margin. Color in alcohol light tan, pigment entirely absent.

Pre-setiger region triangular in shape, about as long as first three thoracic setigers ( Fig. 10A–C ). Prostomium rhomboid to triangular shaped dorsally, triangular shaped ventrally, anteriorly tapering to narrow rounded tip; eyespots absent, nuchal organs narrow slits along posterior margin. Peristomium with two dorsolateral lobes separated by groove from which dorsal tentacles arise; no tentacles present but scars evident in grooves. Ventral surface relatively smooth, not crossed by peristomial grooves; mouth arising at level of first peristomial ring, consisting of simple opening between 6–8 lateral lobes ( Fig. 10C ); proboscis partially emergent on a few specimens.

Branchiae or their stubs present on setigers 2–7 or 8 ( Fig. 10A ), not observed on setiger 9; when present, most branchiae long, thin, rounded in cross section, tapering to rounded tip; branchiae with narrow ciliated groove; internal blood vessel extends along entire length. Juveniles with branchiae observed only on setigers 2–4.

All parapodia biramous with setae near anterior edge of each segment. Thoracic setigers with dense fascicles in dorso-lateral locations on each segment ( Fig. 11A, C ); thoracic notosetae with numerous capillaries (ca. 50–60) in dense fascicles consisting of five or more curved setal rows; neurosetae similarly arranged with capillaries even more numerous (~75+) becoming thicker, almost spinous ( Figs. 10D , 11C ). Abdominal setigers from setiger 10 with setae arranged in long double rows almost entirely encircling body, with narrow dorsal, ventral, and lateral gaps approximating position of parapodia. Setiger 10 with all capillaries arranged in two rows; from setiger 11 anterior row of setae of noto- and neuropodia mostly thicker mucronate or subuluncinate spines ( Figs. 10E–F , 11D ), with posterior row consisting of thin capillaries ( Figs. 10G , 11D ); simple blunt-tipped spines not observed.

Posterior region not present among fragments.

Methyl Green staining. Posterior dorsal areas of prostomium and peristomial lobes retain stain; rest of body lacking distinct pattern.

Remarks. Heterospio guiana n. sp. most closely resembles the Iceland material described by Parapar et al. (2014) as H. longissima sensu Hartman and H. paulolanai n. sp. from off Brazil. However, as discussed above, Hartman’s material is described herein as two different species, both of which are different than the one described by Parapar et al. (2014). One difference between H. longissima sensu Parapar et al. and H. guiana n. sp. is that there are only seven pairs of branchiae on H. guiana n. sp. instead of eight; however, the missing pair may simply not be visible as scars or fully developed on the Suriname specimens. The main differences, however, between the two species are: (1) setiger 9 of H. guiana n. sp. is three times the length of setiger 8 instead of only twice the length, (2) dense fascicles of thick capillaries, which are most numerous on the neuropodia, occur on the thoracic parapodia of setigers 1–9 in H. guiana n. sp. rather than fewer capillaries in fan-shaped fascicles, and (3) abdominal setiger 10 of H. guiana n. sp. has encircling rows of capillaries whereas the Icelandic specimens have an anterior row of subuluncini and a posterior row of capillaries; subuluncini do not begin until setiger 11 on H. guiana n. sp.

Heterospio guiana n. sp. is also similar to H. paulolanai n. sp. The two species differ in that in H. guiana n. sp. setiger 9 is three times longer than setiger 8, branchiae occur on setigers 2–7, the mouth is a simple opening between 6–8 small lateral lobes, and setigers 11–12 have aristate spines in the anterior row of setae and capillaries in the second, whereas in H. paulolanai n. sp. setiger 9 is 2.5 times longer than setiger 8, branchiae occur on setigers 2–8, the mouth is a transverse slit between two large lateral lobes, setiger 11 has aristate spines and capillaries, and setiger 12 has acicular spines in the first setal row and subuluncini and capillaries in the second row.

Etymology. Named for the location of this species in the Guiana region of South America.

Distribution. Off northeastern South America, Suriname, in upper continental slope depths, 520– 550 m.

Figures

FIGURE 10. Heterospio guiana n. sp. A, anterior end (setiger 1–10), dorsal view; B, anterior end (setiger 1–5), dorsal view; C, anterior end, ventral view; D, neuropodial capillary, setiger 4; E–F, neuropodial subuluncini, setiger 12; G, neuropodial capillary setiger 12. A, C, paratype (LACM-AHF Poly 13268); B, D–G, holotype (LACM-AHF Poly 13269).

FIGURE 11. Heterospio guiana n. sp. A, anterior end, dorsal view; B, anterior end, left lateral view; C, setiger 4, anterior view; D, notopodial subuluncini and capillaries, setiger 12. A, holotype (LACM-AHF Poly 13268); B–D, paratype (LACM-AHF Poly 13269).