Euthalenessa fimbriata (Mcintosh)

Pettibone, M. H., 1970, Revision of the genus Euthalenessa Darboux (Polychaeta: Sigalionidae), Smithsonian Contribution to Zoology 52 : 22-24

Euthalenessa fimbriata (Mcintosh)

Figure 14

Thalenessa fimbriata Mcintosh , 1885, p. 144, pi. 19: fig. 10, pi. 23: fig. 4, pi. 24: fig. 5, pi. 25: figs. 1,2, pi. 13A: fig. 13.

Euthalenessa fimbriata .-Darboux, 1900, p. 114.

Euthalenessa digitata .-Knox, 1960, p. 97 (part?). [Not Thalenessa digitata Mcintosh , 1885.]

Material Examined.- Off Port Jackson , Australia, 55-64 meters, hard bottom, Challenger Expedition, Station 163B , 3 June 1874 - holotype of Thalenessa fimbriata ( BMNH 1885: 12: 1: 112 ) .

Type-material.-The holotype consists of a small incomplete specimen, now in 6 fragments, with a total length of about 34 mm, width, including setae, 4 mm, and 77 segments.

Description.-The body has reddish brown, somewhat banded coloration. The elytra are pigmented along their medial and posterior margins. At first they are small and circular, then larger, subtriangular to subreniform (Figure 14 j, k). The 1st pair of elytra lack papillae. The anterior elytra have fringes of papillae extending along most of their lateral borders, with about 15 papillae; more posteriorly, the papillae are confined to the anterior halves of the lateral borders, witil about 13 papillae. The papillae are irregularly dichotomously branched, with 4 to 14 filaments per papilla.

The pharynx was not extended and was not examined.

The fused prostomium and tentacular segment are withdrawn within the anterior few setigers (Figure 14a). The 2 pairs of eyes are located on the anterior oval area of the prostomium, forming bulging ocular lobes; the anterior pair of eyes are elongated, much larger than the posterior pair; the posterior two-thirds of the prostomium is covered dorsally by the anterior segments. The ceratophore of the median antenna extends as a narrow column between the anterior pair of eyes, continuing onto the dorsal bases of the fused tentacular parapodia. The ceratophores of the lateral antennae extend beyond the median ceratophore, where they are also fused to the dorsal sides of the tentacular parapodia; the 3 free antennal styles are subequal in size, short, and subulate. The palps are long, finely tapered, and smooth (information according to Mcintosh; the palps are now missing). The dorsal tentacular cirri are short and tapered; the ventral tentacular cirri are about twice as long as the dorsal. The inner dorsal tentacular ridges extend onto the distal halves of the tentacular lobes; setae are few or nearly absent. The bulbous facial tubercle is visible ventrally, medial to the inner palpal sheadis. A single pair of labial ctenidia is present on the lateral lips.

The parapodia of setigers 2-5 are greatly modified, with well-developed notopodial and neuropodial bracts (Figure 14&-d). The notopodial bracts encircle the compact bundles of notosetae; they are variously slashed, with 2-3 anterior and 1-3 posterior stylodes. The neuropodial bracts include the following: (/) lower-anterior-ventral bracts, greatly elongated and flaring; they are largest on setigers 2 and 3, becoming shorter on setigers 4 and 5; (2) upper-anterior bracts, shorter and wider; their lower distal parts form distinct rounded lobes or ligules, directed inward; (3) lower-posterior bracts, subcorneal, directed upward; and (4) upper-posterior bracts, formed of 5-7 stylodes; on setiger 5, there are 3 upper digitiform stylodes and a lower large subcorneal one. On the following transitional setigers, die lower-anterior and upper-anterior bracts become shorter and truncate, with a notch between; the lower lobes or ligules of die upper-anterior bracts become more prominent; the lower-posterior bracts become smaller, subcorneal; the upper-posterior stylodes are fewer in number - a single one in addition to a large bifid lobe on setiger 6. By setiger 7, die stylodes have disappeared and die posterior bract is continuous, with a shallow distal notch. The long slender compound neurosetae of the anterior setigers have multiarticulate blades, widi 7-10 articles; some of the neurosetae are stouter, with short blades; die stems are smooth or have few spinous rows (Figure 14<r). The dorsal cirri on setiger 3 are short, subulate, borne on short cirrophores. Small ctenidia encircle die elytriphores of setiger 2 and die dorsal cirri of setiger 3.

The branchiae begin on setiger 4. The parapodial ctenidia are large, cup-shaped, 3 per parapodium. The parapodia of the anterior segments have small clubshaped notopodia and large neuropodia (Figure 14eg). The notopodial bracts have a single posterior and 2-3 anterior stylodes. The notosetae form rather small bundles; they are slender, spinous, tapering to capillary tips. The neuropodial acicular lobes are enclosed in anterior and posterior bracts. The C-shaped posterior bracts are diagonally truncate and encircle the C-shaped row of neurosetae. The small lower-anterior bracts are truncate and enclose the lower diagonal row of neurosetae. The larger upper-anterior bracts are rounded, with prominent digitiform lobes or ligules on their lower borders; the upper borders of the bracts curve around the upper diagonal row of neurosetae. The compound neurosetae are relatively slender; the distal tips of the enlarged stems have few faint spinous rows; the blades are short to longer, with 1-2 articles; some of the upper and lower groups are more slender, with longer 3-articled blades (Figure 14g). The ventral cirri are slender, tapering, extending to the distal tips of the neuropodia.

The parapodia of the middle and posterior regions of the body differ in some respects (Figure 14A, "'). The notopodia are similar, having a single posterior stylode and 2-3 anterior stylodes. The neuropodia show marked changes, however. The posterior bracts are more elongate and diagonally truncate. The upper-anterior bracts are smaller and more or less fused with the acicular lobes in the areas where the neurosetae are lacking; the lower ligules are conspicuous, appearing as oval lobes below the tips of the acicular lobes. The neurosetae are longer; their stems have more distinct spinous rows; the blades of the middle neurosetae are shorter to longer, with 1-3 articles; those of the upper and lower series have longer blades, with 4 articles (Figure 14 Í). The ventral cirri are longer, extending beyond the distal tips of the neuropodia.

Distribution.-Off Australia, New Zealand? In 55 to 64 meters.

Remarks.-Knox (1960) referred E. fimbriata to E. digitata . Based on reexamination of the type-specimens, they are herein considered to be distinct species. At least some of Knox's records of E. digitata from the Chatham Islands, New Zealand, in 55 to 283.5 meters, probably refer rather to E. fimbriata . The elytral papillae suggest this: the majority of the specimens were stated to have elytral papillae with more than 12 ramifications; this agrees with E. fimbriata but not with E. digitata . Knox did not describe the blades of the neurosetae.