Saxipendium implicatum (Holland et al. 2012)
Holotype: 36°51' N, 125°33'W, off the central California coast at a depth of 3034 m, in sediment ponds near hard substrate.
[Osborn et al. 2012]
Holotype: 36°51' N, 125°33'W, off the central California coast at a depth of 3034 m, in sediment ponds near hard substrate.
[Osborn et al. 2012]
External description: The color of the proboscis, collar, and the pharyngeal/esophageal region of the trunk is medium orange, whereas the intestinal region of the trunk is beige with a slightly black tint. The length-to-width ratio of the dome-shaped proboscis of S. implicatum is significantly smaller than that of the arrow-shaped proboscis of S. coronatum. Tracts of gonads, visible through the body wall, ran on either side of the trunk. When the worms were entirely exposed on the sea floor, the posterior end was typically seen resting on a tangled mass of the animal's own fecal strand. The 2-mm diameter fecal strand was round in cross-section and about the same color as the surrounding sediment.
Proboscis and Collar: The proboscis is covered with an epidermis of relatively few mucus cells and a sparse meshwork of connective tissue and muscle cells. In the proboscis stalk, the general nervous system is thickened into two proboscis nerves, one on either side of the midline. The collar epidermis includes abundant mucus cells. About midway between the limits of the collar, large muscles appear that insert on the proboscis skeleton. The dorsal collar nerve is incompletely invaginated from the worm's surface, which means the invagination is closed only over for a few hundred micrometers. The main part of the proboscis skeleton is shaped like a crown with projecting spikes and divides the stomochord into sections. This coronate shape of the proboscis skeleton is a peculiarity shared by S. coronatum and S. implicatum.
Pharyngeal/Esophageal region: The posterior horns of the proboscis skeleton are present on either side of the pharynx (unusual for most enteropneusts). The pharynx communicates with the exterior via gill slits. Nerve cords run along the entire length of the trunk. In the esophageal region of the trunk, the endodermal lining is relatively thick and contains moderately abundant mucus cells. The esophageal lumen communicates with the exterior via esophageal canals.
Gonads: Gonads run along the pharyngeal and esophageal region of the trunk just beneath the epidermis. The holotype is a female with numerous ovaries. Each immature ovary contains several small oocytes and non-germinal cells with granular contents. In more mature ovaries, a single large oocyte is present without any detectable non-germinal cells. The diameter of the largest oocytes is approximately 700 μm. Presumably S. implicatum is gonochoric, although male specimens have yet to be collected.
Intestinal region: Posterior to the esophagus commences the intestine, which comprises a very long hepatic region and a short post-hepatic region. The paucity of mesodermal cells along most of the trunk gives the body of the living worm a rather flabby appearance. Along the length of the hepatic intestine, dark brown granules fill most of the endodermal cells and impart a darkish color to the gut. The contents of the lumen of the hepatic intestine are mostly unidentifiable, except for occasional pieces of sponges, echinoderms, diatoms, and foraminiferans, but no mineralized sediment.
[Holland et al. 2012]
Type species: Saxipendium coronatum [Woodwick & Sensenbaugh 1985]
58 observed worms were associated with sediments that had collected in isolated depressions on the surface of ancient lava, and 34 were on mud or among sedimentary rock outcrops. 21 of the worms observed were fully exposed on the sea floor, whereas the other 71 showed only their anterior ends, which protruded out of soft substratum or from behind rock outcrops. The geographic range of S. implicatum appears to be restricted to the Davidson, Guide, and Taney Seamounts region in the eastern Pacific offshore of Central California.
The geographic range of S. implicatumappears to be restricted to the Davidson, Guide, and Taney Seamounts regionin the eastern Pacific offshore of Central CaliforniaThe geographic range of S. implicatumappears to be restricted to the Davidson, Guide, and Taney Seamounts regionin the eastern Pacific offshore of Central California.
[Holland et al. 2012]
Morphologically, Saxipendium implicatum has two unusual features.
1.) The dorsal nerve cord runs for most of its length along the bottom of a shallow invagination that remains open on the side of the collar. The nerve is only briefly covered by a narrow bridge of muscles and epidermis at the extreme posterior extremity of the collar. S. coronatum exhibits no such peculiarity [Woodwick & Sensenbaugh 1985].
2.) The horns of the proboscis skeleton extend posteriorly into the most anterior region of the trunk. S. implicatum is the first species in which the horns have been found to penetrate into the anterior extremity of the trunk.
[Holland et al. 2012]
Holotype: ~22 cm long
Proboscis: 1.3 cm long by 1.2 cm wide
Collar: .6 cm long by 1.4 cm wide
Other observed, uncollected worms: 23 cm, 26 cm, 35 cm
[Holland et al. 2012]
Saxipendium implicatum is a harrimaniid acorn worm found in the deep sea at a depth of ~3000 m off the central California coast, characterized by its contorted fecal strand, medium orange body color, and incompletely invaginated dorsal collar nerve.
[Holland et al. 2012]