Eupolymnia regnans Chamberlin, 1919

Figures 2 D, E, 3A–E

Eupolymnia regnans Chamberlin,1919a: 433, 434, plate 43, Figures 1–3.

Polymnia regnans: Monro 1933: 1072, 1073, Figure 19a, b; Fauchald 1977:56.

Material examined. Syntype, MCZ 2395, Panama Expedition, USFC Albatross, 13 March 1891, coll. Agassiz, location unknown.

Description. Syntype broken in five pieces, measuring altogether around 160 mm in length, with about 157 segments. No pigmentation present after fixation; eyespots not seen. Broad tentacular ridge with several rows of long tentacles. Lips well developed; upper lip large and surrounding most of mouth, lower lip longer, folded, and restricted to ventral side of mouth (Figure 3 B, D). Peristomium forming dorsal ring inserted below prostomium. Three pairs of branchiae on segments 2–4 (now partly detached from body), with first pair largest and decreasing slightly in size from 1st to 3rd pair (Figure 3 A, C); branchiae arranged in a longitudinal row (not evident in Figure 3 C), with each main stalk, long, broad, about half length of entire branchia, and with numerous short compact distal branches. Three pairs of small, pointed lateral lobes on segments 2–4, all similar in size, arranged obliquely ventro-dorsally (Figure 3 E). Eighteen glandular ventral pads from segment 2 onwards, divided horizontally into 2; pads becoming gradually narrower posteriorly (Figure 3 B, D). Rounded nephridial papillae located ventral to notopodia, visible on segments 3–5 only (Figure 3 E). Notopodia cylindrical and long, on segments 4–21. Notochaetae smooth narrow-winged capillaries arranged in 2 irregular rows, showing dorso-ventral increase in length, graded in length within fascicle. Neuropodia from segment 5 (Figure 3 E); uncini arranged in single rows on segments 5–10, subsequently in two rows, arranged face to face, on all remaining chaetigers with notopodia. Uncini decreasing in size posteriorly, with one row of teeth above main fang, small or inconspicuous in some uncini (dental formula MF:1:1–0), and dorsal button situated mid way along between prow and base of main fang pointing towards prow (Figure 2 D). Neuropodia from segment 22 with short tori and dorsal rounded papilla; avicular uncini arranged in single rows to pygidium, with pointed dorsal button mid way along between prow and base of main fang pointing towards prow; dental formula MF:1, with the secondary tooth clearly separated from main fang (Figure 2 E). Some uncini have a knob on this secondary tooth (Figure 2 E). Pygidium as a wide rim surrounding anus.

Remarks. The original description is brief and inadequately illustrated so the only known syntype is redescribed here. Some slight differences between this and the original description can be noticed. Eyespots mentioned by Chamberlin (1919a) are not visible on the syntype, probably due to the effect of the fixation or long term storage. Lateral lobes were not described in the original description although they are present on the syntype as small, pointed lobes, similar in size on all three segments and arranged obliquely. Nephridial papillae are only visible on segments 3–5, although Chamberlin (1919a) described them as present on segments 3–8; this difference is probably due to the poor condition of the syntype, especially on the tegument of these segments. The length of the handle of the posterior uncini resembles that described by Chamberlin but is not as long as recorded by Monro (1933).

Eupolymnia regnans is characterised by having 18 ventral pads whereas other Eupolymnia species have 14 or 15 ventral pads. In addition, the uncini have only one secondary tooth per row above the main fang with two rows in anterior and one in posterior segments, while all other species have more than one tooth per row.