Euthalenessa chacei, Pettibone, M. H., 1970

Pettibone, M. H., 1970, Revision of the genus Euthalenessa Darboux (Polychaeta: Sigalionidae), Smithsonian Contribution to Zoology 52 : 24-28

Euthalenessa chacei , new species

Figures 15, 16

Thalenessa oculata .-Treadwell, 1906, p. 1157 [Not Mcintosh, 1885.]

Thalenessa digitata .-Hartman, 1966, p. 178. [Not Mcintosh, 1885.]

Type-material.- Vicinity of Laysan Island , Hawaiian Islands , 114-238 meters, broken shells and corallines, Albatross Station 3936 , 16 May 1902 - holotype ( USNM 5469 ). The species is named for Dr. Fenner A. Chace, Jr., of die Smithsonian Institution, expressing in a small way my appreciation for his help in reviewing my polychaete manuscripts.

The holotype is incomplete, consisting of anterior and middle fragments, with a total length of 23 mm, width of 4 mm, including setae, and 52 segments. It was found occupying a white parchment-like tube encrusted with fragments of coral sand, foraminiferans, and shell fragments. Whether the tube was of its own making or secondarily occupied is not known. Perhaps it was commensal with a tube-living polychaete. The delicate condition of the body and elytra indicates a probable tube-dwelling existence for the species.

Description.-The body lacks color. The elytra are very delicate and transparent. They change in size and shape along the body. At first they are small, oval, then large, subrectangular, subreniform to subcordiform(Figure \5h-k). The first pair of elytra lack papillae. The anterior elytra have fringes of papillae extending along most of their lateral borders, with 8-11 papillae; more posteriorly, the papillae are confined to the anterior halves of the elytral borders with about 8 papillae. Most of the papillae are irregularly palmately or dichotomously branched, with 3 to 9 filaments per papilla.

The pharynx was not extended and was not examined.

The fused prostomium and tentacular segment are withdrawn within die anterior few setigers (Figure15a). The 2 pairs of pale eyes are moderately large and closely approximated, located on the anterior oval area of the prostomium; die anterior pair is larger than the posterior pair; die posterior two-thirds of the prostomium is covered dorsally by setigers 2-5. The ceratophore of the median antenna extends from a median area between the anterior pair of eyes, extending onto the dorsal sides of the tentacular parapodia, which are fused along their medial bases. The ceratophores of die lateral antennae, which are also fused to die dorsal sides of die tentacular parapodia, extend to die same level as die median ceratophore; the 3 free antennal styles are subequal in size, short, and subulate. The long, tapering palps, emerging between low inner and outer palpal sheaths, extend posteriorly to segment 16. The dorsal tentacular cirri are short and tapered; die ventral tentacular cirri are almost three times as long as the dorsal. The inner dorsal tentacular ridges are found on die distal fourth of die tentacular lobes, widi 2 groups of capillary setae emerging laterally from near both ends of die ridges; die setae are moderate in number. The bulbous facial tubercle is visible medial to die inner palpal sheaths; a pair of small labial ctenidia is found on the lateral lips.

The parapodia of sedgers 2-5 are gready modified, having well-developed noto- and neuropodial bracts (Figure 15b-g). The notopodial bracts encircle die spreading bundles of notosetae; die bracts have 2-3 anterior and single posterior stylodes. The neuropodial bracts consist of the following: (/) lower-anterior-ventral bracts, gready enlarged and flaring; they are largest on setigers 2 and 3, becoming shorter on setigers 4 and 5; (2) upper-anterior bracts, shorter and wider; the lower distal parts form distinct rounded lobes or ligules, directed inward; (3) lower-posterior bracts, subcorneal and directed upward; (4) upper-posterior bracts formed of digitiform stylodes in number of 4-5; on setiger 5, the lower stylode is much larger than the others, similar in size to die posterior-lower bract (Figure15/). Setiger 6 is transitional: the lower-anterior and upper-anterior bracts are shorter and truncate, with a notch between and with a short rounded ligule; the lower-posterior bract is small; die upper-posterior stylodes consist of a digitiform upper one and large rounded lower one - much larger than die lower-posterior bract. From setiger 7 on, die upper stylodes have disappeared and die posterior bract is continuous. The long slender compound neurosetae of the anterior setigers have multiarticulate blades with 6-9 articles; some shorter stouter ones have 2-4 articles; both types have bifid hooked tips; die stems are smoodi or have faint spinous rows (Figure 15c, g). 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 (Figure 15b, d).

The branchiae begin on setiger 7. The parapodial ctenidia are large, cup-shaped, 3 per parapodium. The parapodia of die anterior segments have small clubshaped notopodia and larger neuropodia (Figure I6a-c). The notopodial bracts have single subtrianguIar posterior and 1-2 anterior stylodes. The notosetae form rather small bundles; diey are slender, spinous, and taper to capillary tips. The neuropodial acicular lobes are enclosed in anterior and posterior bracts. The C-shaped posterior bracts are diagonally truncate and enclose the C-shaped row of neurosetae. The smaller lower-anterior bracts are truncate and enclose die lower diagonal row of neurosetae. The larger upper-anterior bracts are diagonally truncate, widi a more or less distinct rounded lobe or ligule on die lower border; die ligules are directed inward below die tips of die acicular lobes; die upper borders of die bracts curve around die upper diagonal row of neurosetae. The compound neurosetae are radier stout; die distal tips of the enlarged stems are smooth or have few faint spinous rows. Most of the neurosetae have short blades; some of upper neurosetae have longer 2-articled blades; some of the lower ones have 2- to 3-articled blades (Figure 16c). The ventral cirri are slender, tapering, extending to the distal tips of the neuropodia.

The parapodia of the middle region of the body differ in some respects (Figure 16d-g). The notopodia are similar, having only a single stylode on die acicular lobe. The neuropodia show marked changes. The posterior bracts are more elongate and diagonally truncate. The upper-anterior bracts are smaller and more or less fused widi die acicular lobes in die areas where die neurosetae are lacking; diis includes dieir lower ligules. The neurosetae are longer, dieir stems may have more numerous distinct spinous rows, and die blades are longer; die middle neurosetae are stouter, dieir blades having 2-3 articles; die upper neurosetae are more slender, dieir blades having 3-5 articles; die lower neurosetae are slender, dieir blades having 4-5 articles (Figure 16/). The ventral cirri are longer and extend beyond the distal tips of die neuropodia.

Distribution.-Hawaiian Islands. In 144 to 238 meters.

Remarks.-The holotype of E. chacei was previously identified by Treadwell (1906) as Thalenessa oculata Mcintosh . The record of T. digitata by Hartman(1966) is based on Treadwell's record.