Ritteria ambigua, Deland & Cameron & Rao & Ritter & Bullock, 2010
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publication ID |
https://doi.org/ 10.11646/zootaxa.2408.1.1 |
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publication LSID |
lsid:zoobank.org:pub:9BBB84BB-239C-41EA-9CFC-682449F96281 |
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persistent identifier |
https://treatment.plazi.org/id/101A87CA-FF95-FFBA-DBA6-FEE9FF2FFC9B |
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treatment provided by |
Felipe |
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scientific name |
Ritteria ambigua |
| status |
n. gen. et n. sp. |
Ritteria ambigua View in CoL n. gen. et n. sp.
( Figs 2G View FIGURE 2 ; 8A–G View FIGURE 8 )
Material examined. A single anterior fragment was collected by Dr W. K. Fisher at Station 4508 of the Albatross expedition, off Point Pinos, California (36°38' N, 121°56' W), on May 20, 1904 in soft green mud at a depth of 600 to 700 meters. This specimen, accession no. NMNH 58885 View Materials , is here designated holotype GoogleMaps and 1132793 is the paratype.
External features ( Fig. 2G View FIGURE 2 ). Total length unknown; in preserved material from a single specimen proboscis is short, being ca. 3 mm long and 4 mm wide, collar extremely short and broad, being ca. 2 mm long dorsally, 2.7 mm ventrally and ca. 4.5 mm wide Branchial region between 10–15 mm long. Collar with expanded rim at posterior edge. Two pairs of genital ridges present on dorsolateral sides, commencing immediately behind collar, with gill pores situated along lateral grooves formed by these ridges. A small ventral muscular ridge present, hepatic lobes absent. In living material proboscis is coral red, collar is deep vermilion to poppy red, posterior margin of collar and trunk are bright orange.
Internal features. Circular-muscle-fiber layer of proboscis thinner than nerve-fiber layer, amounting to only 3 or 4 fibers in thickness. Nerve-fiber layer thickened along middorsal groove into cord-like structure ( Fig. 8A View FIGURE 8 ). Longitudinal muscle fibers not split into radial bundles or grouped into circular rings but uniformly scattered ( Fig. 8A View FIGURE 8 ). Proboscis coelomic cavity commencing along with anterior tip of proboscis complex. Stomochord large and conspicuous with broad lumen at tip and no lumen through middle region. Ventrolateral diverticula of lumen fused, while the lumen in neck is broken and frequently obliterated. Walls of stomochord in this region laminated by strand-like extensions from body of skeleton ( Fig. 8A View FIGURE 8 ) and here appears broken down into several bits by these strands ( Fig. 8F View FIGURE 8 ). These extensions of collagenous material give skeletal plate a distinctive coronate form that closely resembles that of Saxipendium coronatum . Just before joining buccal epithelium, central part of neck of stomochord acquires distinct lumen. Ventral proboscis septum runs along midventral line of stomochord, stopping short of its tip, dorsal septum absent. Proboscis skeleton quite massive, with large broad keel and wide plate ( Fig. 8F View FIGURE 8 ). Normally formed left proboscis pore present, opening into anterior neuropore by a left vesicle ( Fig. 8F View FIGURE 8 ).
Collar lacking dorsal and ventral septa. A single dorsal root emerging from collar nerve cord in posterior third of collar ( Fig. 8H View FIGURE 8 ). Perihaemal diverticula ( Fig. 8C,H View FIGURE 8 ) confined to collar, extending only up to level of opening of stomochord into buccal cavity. Collar longitudinal muscles well developed, forming triangular bundles on each side of collar lumen ( Fig. 8C View FIGURE 8 ). No peribuccal diverticula. Collar canals short, horizontal, with dorsal infolding as in Ptychoderidae ( Fig. 8D,G View FIGURE 8 ). Skeletal cornua extending to posterior extremity of collar but confined to dorsolateral aspect throughout ( Fig. 8C,D View FIGURE 8 ). Ventral longitudinal muscles poorly developed, not forming bundles or ridges.
Branchial portion of pharynx equal in size to ventral portion. Gonads arranged in two pairs of dorsolateral ridges ( Fig. 8E View FIGURE 8 ) but not forming wings. Branchial openings in form of pores arranged along groove formed between the two genital ridges on either side. Consequently, unlike in Stereobalanus , branchial basket not visible from outside. Instead, branchial sacs ( Fig. 8E View FIGURE 8 ) opening out by branchial pores situated dorsolaterally. Ventral longitudinal musculature forming a small ridge on ventral surface of trunk. Presence of intestinal pores not determinable.
Remarks. From the above description it can be seen that this species does not fit into any of the other genera of the family. In the possession of dorsal gonads it resembles Harrimania and Stereobalanus , but these genera are characterized by proboscis muscles arranged in radial plates. Stereobalanus shares not only the dorsal and lateral gonads but also the apparent degeneration of the neck region of the stomochord. Among other features, the well-developed proboscis pore, and collar canals are enough to distinguish Ritteria from Stereobalanus . The differences from other genera are even more numerous.
The resemblances of Ritteria to other enteropneusts are rather varied, but, as usual in this group, cannot all signify close relationship. The similarities between Ritteria and Harrimania , and between Ritteria and Stereobalanus , are respectively suggestive of a common trend toward the degeneration of several organs while increasing the emphasis on gonads. Although not conforming to the familial characters, Ritteria even resembles the Ptychoderidae in the relatively spacious cardiac vesicle and the extent of the ventral septum of the proboscis.
While not putting undue weight on these similarities, by no means unique in this group, we find the situation suggestive of the trivial name ambigua .
The defining characters of Ritteria ambigua are listed below:
A. Short proboscis and collar.
B. Longitudinal musculature of the proboscis is uniformly scattered.
C. Proboscis skeleton plate is coronate with extensions of collagen through the stomochord walls.
D. Only the ventral mesentery of the proboscis is present (no mesentery in the collar and trunk).
E. Left proboscis pore opening into an anterior neuropore.
F. Degeneration of the proboscis neck.
G. Presence of a nerve root in the collar nerve cord.
H. Well-developed horizontal collar canals with a dorsal infolding.
I. Two pairs of dorsolateral genital ridges starting immediately behind the collar.
No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.
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