Hesione helenensis Salazar-Vallejo 2018, n. sp.

Hesione helenensis n. sp.

(Fig. 20)

urn:lsid:zoobank.org:act: F44B445E-71C8-493B-B59F-2B193435A522

TYPE MATERIAL. — South Atlantic Ocean. Holotype, USNM 33148, and one paratype, USNM 1479052, Saint Helena Island, James Bay, IV.1964, A. Loveridge coll. [paratype 39 mm long, 4 mm wide; slightly distorted; anterior end compressed; dorsal cirrostyles swollen basally, multiarticulated; chaetal lobes markedly contracted, invaginated into neuropodia; acicular lobes barely seen, rounded, upper tine 3-4 times longer than lower one; ventral cirri basally swollen, longer than neuropodia, slightly articulated; posterior end truncate; anus with about 6 anal papillae].

ETYMOLOGY. — The species name is an adjective derived from Saint Helena island, and as in some other similar names, the last vowel in the proper name is suppressed, and the suffix - ensis is added to indicate its current distribution.

DISTRIBUTION. — Only known from Saint Helena island, in subtidal rocky bottoms.

DIAGNOSIS. — Hesione with prostomium slightly curved laterally; parapodia with dorsal cirri basally swollen, dorsal cirrophore twice as long as wide; larger acicula blackish; acicular lobe single, short, massive, blunt, upper tine 3 times longer than lower one; neurochaetal blades bidentate, 4-6 times as long as wide; subdistal tooth smaller; guards approaching distal tooth.

DESCRIPTION

Holotype, USNM 33148, complete, subcylindrical, tapered posteriorly, without pigmentation (Fig. 20A) in ethanol; most cirri and many neurochaetal blades broken; left parapodium of chaetiger 9 removed (kept in vial). Body 39 mm long, 4 mm wide.

Prostomium slightly as wide as long, anterior margin projected anteriorly, lateral margins rounded, posterior margin with a shallow cleft, about 1/5 as long as prostomial length, longitudinal depression slight (Fig. 20B). Antennae minute, left one visible, fusiform, 2-3 times as long as wide, about as long as interocular distance. Eyes brownish, anterior ones larger and more separated than posterior ones.

Tentacular cirri long, thin, broken, longest one (incomplete) reaches chaetiger 3. Lateral cushions low, smooth, barely projected, most divided into 2 or 3 regions.

Parapodia with chaetal lobes about as long as wide, truncate; dorsal cirri with cirrophores about twice as long as wide (Fig. 20C); cirrostyles basally swollen, annulated, articulated medially and distally, as long as body width (tips lost). Ventral cirri with cirrostyles basally swollen, surpassing chaetal lobe, darker than parapodia (if observed in compound microscope preparations).

Neuraciculae blackish, tapered, only one visible. Acicular lobe double, upper tine blunt, as long as wide, 4 times longer than lower tine blunt (Fig. 20C [insets]).

Neurochaetae about 20 per bundle (Fig. 20D), blades bidentate, 4-6 times as long as wide, decreasing in size ventrally, each with smaller subdistal teeth, and guards (most broken) reaching subdistal teeth (Fig. 20D [insets]).

Posterior region tapered into a blunt cone, dorsal surface rugose (Fig. 20E); pygidium smooth, anus with 7 blunt papillae.

Pharynx partially exposed, anterior margin slightly eroded, dorsal papilla not seen. Oocytes not seen.

REMARKS

Hesione helenensis n. sp. resembles Northeastern Atlantic or Mediterranean specimens of H. pantherina Risso, 1826, and it could be confused with it. However, as indicated in the key below, H. helenensis n. sp. resembles H. praetexta Ehlers, 1887 reinstated. The main difference is that in H. helenensis n. sp. dorsal and ventral cirrostyles are basally swollen, and this feature is unique for the genus, and present throughout the body, although in posterior chaetigers ventral cirrostyles are less markedly swollen. Further, these swollen areas appear darker when parapodia are mounted and observed in the compound microscope.