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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Deontostoma

Deontostoma Filipjev, 1916 (ref. ID; 3570)

Enoplida Filijev, 1929: Family Leptosomatidae Filipjev, 1916: Subfamily Thoracostomatinae De Coninck, 1965 (ref. ID; 3570)

Leptosomatidae (ref. ID; 7791)

ref. ID; 3570

Type species

Thoracostoma arcticum Ssaweljev, 1912, designated by Filipjev, 1916 (ref. ID; 3570)
  1. Deontostoma anchorilobatum (Allgen, 1947) Platonova, 1962 (ref. ID; 3570)
    Syn; Thoracostoma anchorilobatum Allgen, 1947 (ref. ID; 3570)
  2. Deontostoma angustifissulatum (Mawson, 1956) (ref. ID; 7791)
  3. Deontostoma antarcticum (Linstow, 1891) Filipjev, 1916 (ref. ID; 7791) or (Linstow, 1892) Filipjev, 1916 (ref. ID; 3570)
    Syn; Leptosomatum antarcticum Linstow, 1892 (ref. ID; 3570); Thoracostoma polare Cobb, 1914 (ref. ID; 3570)
  4. Deontostoma arcticum (Ssaweljev, 1912) Filipjev, 1916 (ref. ID; 3570)
    Syn; Thoracostoma arcticum Ssaweljev, 1912 (ref. ID; 3570); Thoracostoma elongatum Ditlevsen, 1926 (ref. ID; 3570)
  5. Deontostoma aucklandiae (Ditlevsen, 1921) Platonova, 1962 (ref. ID; 3570)
    Syn; Thoracostoma aucklandiae Ditlevsen, 1921 (ref. ID; 3570)
  6. Deontostoma brunni (Wieser, 1956) (ref. ID; 7791)
  7. Deontostoma californicum Steiner & Albin, 1933 (ref. ID; 3570, 7791)
  8. Deontostoma demani (Mawson, 1956) Hope, 1967 (ref. ID; 3570)
    Syn; Thoracostoma demani Mawson, 1956 (ref. ID; 3570)
  9. Deontostoma karachiense (Timm, 1959) Hope, 1967 (ref. ID; 3570)
    Syn; Thoracostoma karachiense Timm, 1959 (ref. ID; 3570)
  10. Deontostoma jae (Inglis, 1964) (ref. ID; 7791)
  11. Deontostoma lobatum (Steiner, 1916) Platonova, 1962 (ref. ID; 3570)
    Syn; Thoracostoma lobatum Steiner, 1916 (ref. ID; 3570)
  12. Deontostoma magnificum (Timm, 1951) Platonova, 1962 (ref. ID; 3570)
    Syn; Thoracostoma magnificum Timm, 1951 (ref. ID; 3570); Thoracostoma pacificum Murphy, 1965 (ref. ID; 3570)
  13. Deontostoma montredonense (Marion, 1870) Filipjev, 1916 (ref. ID; 3570)
    Syn; Thoracostoma montredonense Marion, 1870 (ref. ID; 3570)
  14. Deontostoma papillatum (Linstow, 1903) Filipjev, 1916 (ref. ID; 3570)
    Syn; Leptosomatum papillatum Linstow, 1903 (ref. ID; 3570)
  15. Deontostoma polare (Cobb, 1914) (ref. ID; 7791)
  16. Deontostoma timmerchioi Hope, 1974 (ref. ID; 7791)
  17. Deontostoma washingtonense (Murphy, 1965) Hope, 1967 (ref. ID; 3570)
    Syn; Thoracostoma washingtonense Murphy, 1965 (ref. ID; 3570)

Deontostoma timmerchioi Hope, 1974 (ref. ID; 7791)

Descriptions

Marine nematode. Body unusually large, gradually tapered anteriorly from near midbody region; head truncate, tail bluntly conical. Cuticle smooth. Head with usual arrangement of six labial papillae and 10 cephalic setae. Short cervical setae in lateral, subdorsal, and subventral longitudinal rows from near cephalic suture to region of ocelli. Posterior to this, setae irregularly distributed over body surface. Tail with one to several subterminal setae. Cephalic capsule without prominent anterior lobes or tropis and with usual six posterior lobes. Each posterior lobe broad and usually anchor-shaped with anteriorly directed tines. Posterior margin of each lobe truncate or rounded, with notches and/or incisions. Intralobar lacunae often present and irregular in size and shape; seldom more than two per lobe. Amphid circular to oval with faintly perceptible walls. Stoma triradiate (closed) to triangular (open). Orifice of stoma enclosed by one dorsal and two subventral microlabia (Hope 1967) set off by shallow grooves. Each microlabium bearing one pair of acutely-conical, anteriorly directed odontia. Odontia of each subventral pair separated at their bases; interval between tips of each member of paired subventral odontia 17-19 µm. Each member of paired odontia on dorsal microlabia broadly joined at their bases; tips of these odontia directed ventrally as well as anteriorly; tips separated by interval of 10-11 µm in two specimens measured. Dorsal wall of stoma with single onchium near level of amphids. Esophagus conical and with paired ocelli; each ocellus comprised of spherical lens-like structure and reddish-brown cyathiform pigment spot. Dorsal gland orifice a short distance anterior to ocelli. Tail bluntly conical and tapered almost entirely on dorsal side in males. Terminus with caudal gland pore. Caudal glands outstretched and extending anterior to rectum. (ref. ID; 7791)
  • Males: As in general description. Subventral supplements in one longitudinal series on each subventral side of body. Each series consisting of setae extending anteriorly from just posterior to the cloacal vent to where gradually replaced by papillae in shallow depressions on short transverse ridges of cuticle. Cuticular swelling not internally differentiated, that is, without closely pakced rod-like structures present in D. californicum Steiner & Albin, 1933. Longitudinal series of setae very slightly arched ventrally at level of cloacal vent. Canal of ventromedian supplement surrounded by intracuticular, transversely oval disc. Spicula scimitar-shaped; moderately arched, especially in anterior portion. Capitulum not enlarged or otherwise distinct from calomus; calomus slightly arched toward venter. Lamina anteriorly wide and tapered to posterior tip; velum extending over slightly more than anterior half of lamina. Gubernaculum duplicate; corpus of each half consisting of parallel bars fused at each end. Ventral end of corpus bearing several distinct transverse striations. Corpus with anteriorly directed crus; crus slender and without distal hook. Male reproductive system diorchic; testes opposed. (ref. ID; 7791)
  • Females: As in general description. Reproductive system amphidelphic and reflexed. (ref. ID; 7791)

    Remarks

    The species of Deontostoma can be grouped according to the numbers, shape, and orientation of odontia, which are teeth located on the medial surface of the lips. In one major group, the odontia seem to have migrated from the dorsolateral corners of the stoma to a more central position on the dorsal lip. In this case, their bases appear to have fused to produce a bifid or two-lobed protrusion. This structure, termed the cordiform piece by de Man (1904), may consist of blunt lobes, as in the case of D. antarcticum (von Linstow, 1891) Filipjev, 1916, or of pointed tooth-like structures, as in the case of the species just described. In having pointed odontia, D. timmerchioi is similar to Deontostoma angustifissulatum (Mawson, 1956) n. comb., D. brunni (Wieser, 1956) n. comb., and D. jae (Inglis, 1964) n. comb. However, the tips of the dorsal odontia of D. timmerchioi are directed anteriorly and ventrally, while in D. brunni they are directed anteriorly and laterally, and in D. angustifissulatum and D. jae, as well as D. antarcticum, they are directed laterally. The odontia of the subventral lips also vary. In D. timmerchioi, D. angustifissulatum, D. jae and D. brunni each member of each pair is similar in size and shape. In D. antarcticum, the ventral odontium of each pair is a relatively large, blunt lobe, directed ventromedially, while the dorsal member of each pair is relatively small, acute, and dorsomedially directed. Deontostoma timmerchioi also differs from D. brunni by the larger ratio of the distance between the anterior margin of the head and the posterior margin of the cephalic capsule, to the head width at the level of the posterior margin of the cephalic capsule. The head is also more truncate than in D. brunni, and males of D. brunni are reported devoid of papilloid subventral supplements, whereas they are present in D. timmerchioi. Other interspecific differences may lie in the structure of the ventromedian supplements, spicula, and gubernaculum; but these structures have to been adequately described and illustrated, except for D. antarcticum by de Man (1904). In that species, the lamina is not as wide nor as abruptly set off from the calomus, and the lamina does not taper posteriorly so much nor so uniformly as it does in D. timmerchioi. The gubernaculum is quite similar in these two species, except that the anterior end of the crus is bent in D. antarcticum. Although the identity of Deontostoma polare (Cobb, 1914) remains doubtful, it must be given consideration here, since its type locality is at Cape Royds Station on Ross Island approximately 22 miles from the type locality of D. timmerchioi. While Cobb's description and single illustration of the head do not supply information concerning the relevent taxonomic characters used for this genus today, it seems unlikely that his specimens are conspecific with D. timmerchioi. This conclusion rests mainly with the great disparity in their over-all lengths. Deontostoma timmerchioi males are 39.2-44.9(42.1+/-1.9) mm, and the females are 31.2-46.8(40.8+/-6.0) mm, while Cobb's adult specimens were 19.0 and 19.3 mm long. Wieser (1953) and Mawson (1958) have regarded D. polare as a synonym of D. antarcticum. This seems very possible since D. antarcticum was also present in Viglierchio's collection from nearby McMurdo Station. The lengths of these specimens were between 17 and 18 mm. (ref. ID; 7791)
  • Ventromedian Supplement. During the course of obtaining light and scanning electron micrographs for the above taxonomic description, detailed information concerning the ventromedian supplement was acquired. In the absence of sufficient specimens of D. timmerchioi to be spared for the preparation of histological sections, additional information was extrapolated from a study of such preparations of Deontostoma californicum Steiner & Albin, 1933. Technique used in making sections of the latter species has been described elsewhere (Hope 1969). As indicated in the taxonomic description, this structure lies on the ventral body surface a short distance anterior to the cloacal vent and is present in males of most members of Leptosomatidae. Most previous observations of this organ are limited to whole mount preparations, with the animal viewed laterally for taxonomic study. From such studies the ventromedian supplement is believed to consist of cells associated with a canal through the cuticle and of intracuticular modifications surrounding the canal. In Deontostoma timmerchioi the canal is lined with a very light refractive layer of cuticle. The lining varies in thickness and seems to have a seam on the anterior surface. A cylinder of apparently homogenous cuticle surrounds the canal lining. A cylinder of apparently homogenous cuticle surrounds the canal lining and extends from the inner surface of the cuticle to the external surface where, in a ventral view of the body, it appears as a narrow granular ring. The canal and cylinder are, in turn, located within a disc-shaped region of the middle and possibly the internal layers of cuticle. At its inner margin, nearest the cylinder, the disc occupies nearly the full width of the cuticle, excluding the external layer; but the thickness of the disc diminishes at its outer perimeter. This disc may be recognized, when viewed from the ventral surface, by its finely granular appearance. The canal and cylinder are also circumscribed by an oval field of minute striae in the external layer of cuticle. These striae extend to the surface as demonstrated by scanning electron micrographs. The lumen of the canal at the exterior is closed by the cortical layer of the cuticle, except for a pore, near the limits of resolution for the light microscope, located just posterior to the center of the underlying canal. At the opening of the pore, there is a minute organ which seems to be the end of a trough or tube. A tube-like structure, visible with the light microscope, also extends from the external layer of the cuticle, through the canal and then passes anteriorly from the internal end of the canal into the hypodermis to the left of the sagittal plane. Histological sections through the region of the ventromedian supplement of Deontostoma californicum have confirmed the presence of a tube-like structure. It passes from the supplement into the hypodermis as a narrow tube with relatively well-defined walls and, after short distance, begins to increase in diameter. At this point there appears to be a dilation of the lumen of the tube enveloping what may be a filament. From this point appears that the tube-like structure has continuity with the process of a cell. The cell process extends anteriorly, slightly to the left of the sagittal plane, to about the level of the anterior end of the retracted spicula. There it turns dorsally, passing along the left lateral surface of the ventral nerve cord. Finally, it merges with a cell 16.4 µm in diameter, having a nucleus 12.2 µm in diameter. A basophilic fiber extends throughout the length of the cell process which, together with the light staining properties of the cytoplasm, makes it distinguishable from hypodermal tissue. The cell is closely associated with numerous cells comprising a ganglion of the ventral nerve cord. (ref. ID; 7791)

    Habitat

    From interspicular spaces of living sponge, Rosella antarctica antarctica Schulze & Kickpatrick, 1940, at 57 m depth. (ref. ID; 7791)

    Type locality

    McMurdo Station, off Hut Point, Ross Island, Antarctica. (ref. ID; 7791)

    Type specimens

    Holotype (Male): USNM No.50584. Allotype (Female): USNM No.50585. Paratypes: Males USNM Nos.50586-50591, Females USNM Nos.50592-50602, Juveniles USNM Nos.50603-50604. (ref. ID; 7791)