Comprehensive Description

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General Description

Live specimens are yellow to red in colour. Adult live specimens from Santa Cruz Basin formed a red, moving ‘carpet’ on the surface of the whale bones and the associated sediments. In the San Diego Trough, specimens formed an undulating carpet on the sediments surrounding the skeleton. The specimens from the Santa Cruz Basin faded to a yellow-white colour when preserved. The length is up to 40mm, with 91 segments. The body shape is elongated with a slight tapering at the posterior and anterior ends. There are long cirri and well developed parapodia that give a shaggy and ruffled look.

The prostomium is reduced and ventrally displaced, but is not visible dorsally. Minute digitiform paired antennae are inserted anteroventrally. Median antenna, eyes, caruncle, and a pronounced nuchal organ are absent. The palps are small, spherical, and are inserted ventrally, directly anterior to the mouth. There are elongated ciliary patches present posteriorly and ventrally on the prostomium. The retracted proboscis is visible through the epidermis and terminates posteriorly in segment 5–6. The feeding apparatus were retrieved from segment 5 in a dissected small specimen from the San Diego Trough only. The feeding apparatus are hyaline, fragile, and resembles two stylets attached to each other at the base, with a length of 200 mm. They are not visible through the epidermis. Feeding apparatus were not found in large specimens.

Segment 1 is reduced, with chaetae and aciculae being absent. There are dorsal tentacular cirri that are fusiform, and directed forward, partially fused with segment 2. Segments are biramous with dorsal and ventral cirri, and there are dorsal and ventral single aciculae from segment 2. The parapodial lobes of segment 2 are reduced, with tentacular cirri that are directed forward and chaetal fascicles that are inserted directly on the segment. The noto- and neuropodia are well-developed from segment 3 onwards.

The notopodia have dense ciliary patches on the front and back sides. The dorsal cirrus is inserted distally, and the cirrophore is weakly developed. Notochaetae 10–22 are round spines, inserted distally on the notopodia, and are partly surround the dorsal cirrus. There are different shaped notochaetae in large and small specimens.

The notochaetae in large specimens have an external longitudinal striation, fine frays on the convex side of the distal half, whilst serration is absent. They have a length <500 um, a width <50 um, and are internally chambered.

The notochaetae in small specimens have an external fine longitudinal striation, and are serrated, with minute denticles that alternate in two directions. They have a length <275 um, a width <7.5 um, and are internally chambered.

The neuropodium in the mid-body segments are slightly longer than the notopodium, with ventral cirrus inserted basally, posteriorly directed, fusiform in short with a short cirrophore. Ciliary patches are present but are fewer than in the notopodium. A single neuroacicula is present and extends to end of acicular lobe. The acicular prechaetal lobe is pronounced and pointed. The neurochaetae are compound unidentate falcigers, with bifid heterogomph shafts that are chambered, and are inserted distally in two loosely defined groups; the upper 3–4 with long slender finely serrated blades, and the lower blades are gradually shorter and wider.

There is one transverse row of ciliary patches ventrally on each segment.

The pygidium is rounded, reduced, and posteriorly flattened. The pygidial cirri are paired, a single pygidial projection is absent, and the anus is terminal.

(Dahlgren et al., 2004).


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