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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Rhynchonema

Rhynchonema Cobb, 1920 (ref. ID; 3571)

Monhysterida Filipjev, 1929: Family Monhysteridae De Man, 1876: Subfamily Rhynchonematinae De Coninck, 1965 (ref. ID; 3571)

Family Monhysteridae (ref. ID; 7629)

ref. ID; 3571

Type species

Rhynchonema cinctum Cobb, 1920 (ref. ID; 3571)
  1. Rhynchonema amakusanum Aryuthaka, 1989 (ref. ID; 1765 original paper)
  2. Rhynchonema brevituba Gerlach, 1953 (ref. ID; 3571)
  3. Rhynchonema cinctum Cobb, 1920 (ref. ID; 3571)
  4. Rhynchonema deconincki Vitiello, 1967 (ref. ID; 3571)
  5. Rhynchonema dispar Gourbault, 1982 (ref. ID; 1765)
  6. Rhynchonema fossum Lorenzen, 1975 (ref. ID; 1765)
  7. Rhynchonema gerlachi Vitiello, 1967 (ref. ID; 3571)
  8. Rhynchonema hirsutum Hopper, 1961 (ref. ID; 3571)
  9. Rhynchonema impar Lorenzen, 1975 (ref. ID; 1765)
  10. Rhynchonema kikuchii Aryuthaka, 1989 (ref. ID; 1765 original paper)
  11. Rhynchonema longituba Gerlach, 1953 (ref. ID; 3571)
  12. Rhynchonema lyngei (Allgen, 1940) (ref. ID; 3282 redescribed paper) or (Allgen, 1940) Gerlach, 1953 (ref. ID; 3571)
    Syn; Leptolaimus lyngei Allgen, 1940 (ref. ID; 3571)
  13. Rhynchonema ornatum Lorenzen, 1975 (ref. ID; 1765)
  14. Rhynchonema scutatum Lorenzen, 1971 (ref. ID; 7629 original paper) or 1972 (ref. ID; 3571)
  15. Rhynchonema subsetosum Murphy, 1964 (ref. ID; 3571)
  16. Rhynchonema tremendum Lorenzen, 1975 (ref. ID; 1765)
  17. Rhynchonema wieseri Hopper, 1961 (ref. ID; 3571)

Rhynchonema amakusanum Aryuthaka, 1989 (ref. ID; 1765 original paper)

Diagnosis

In contrast to R. kikuchii n. sp., the variation of body measurements is rather normal. This species is probably most closely related to R. ornatum Lorenzen, 1975 as suggested by the presence of lateral longitudinal ridges (not present in other Rhynchonema species), the shape of the anterior end, the size of amphids and the shape of the spicules. In contrast to R. amakusanum n. sp., in R. ornatum. The number of annules anterior to the amphids is 33 instead of 24-29, the body is longer and slenderer, and longitudinal ridges nearly invisible in females (clearly visible in R. amakusanum n. sp.). (ref. ID; 1765)

Descriptions

This species is commonly found in Amakusa, south Japan, not only in the low tide zone beach, but also in the seagrass bed. However, its occurrence was restricted to the sediment, and was never found on the seagrass leaves. (ref. ID; 1765)
  • Male: The general form of the specimens is similar to R. kikuchii n. sp., but the body is stouter. The cuticle is strongly annulated and provided with two rows of lateral longitudinal ridges on each side of the body. Annules and ridges project forwardly in anterior part and backwardly in the posterior part of the body. The reversal of orientation occurs at about 47-50% of body length. The ridges are especially prominent between the region of the nerve ring and anus. The head bears 6 cephalic setae of 4-6 µm length (about 1.2-1.6 times of head diameter). The stoma is about 50-57 µm long. The amphids are constantly located at the end of the stoma. The amphids are circular and of similar size in both sexes (6 µm length and 5 µm width). 26-28 annules lie between the anterior end and anterior edge of amphids. The pharynx expands a little bit at its posterior end. The small cardia protrudes into the cylindrical intestine. 12 rows (2 subdorsal, 2 subventral and 4 rows at each lateral side) of 7-15 µm long somatic setae occur on the body-surface. The testes are paired and opposed with the anterior one lying to the left and posterior to the right side of the intestine. The spicules are of equal size, curved, 27-30 µm long, and surrounded by the gubernaculum which bears a median cuticularized projection (3.8-4.2 µm long) and a pair of symmetrical apophyses. The annules in the anal region are slightly inflated. The tail is conical, ventrally curved and bears a terminal spinneret. Two caudal glands are clearly visible. (ref. ID; 1765)
  • Female: The general form is similar to the male specimens. Body length and body width are seemingly larger than in males. The length of stoma is about 50-61 µm. There are 24-29 annules in front of the anterior edge of amphids. The rows of lateral ridge occur similarly in male. The reproductive system is monodelphic, prodelphic and outstretched and reaches the vulva which is a common shape at 68-73% of body length. The ovary lies to the left of the intestine. (ref. ID; 1765)

    Rhynchonema kikuchii Aryuthaka, 1989 (ref. ID; 1765 original paper)

    Diagnosis

    Previously, asymmetry of spicules in Rhynchonema has been known from R. tremendum Lorenzen, 1975, R. impar Lorenzen, 1975, R. fossum Lorenzen, 1975 and R. dispar Gourbault, 1982. In all cases, the right spicule is larger than the left one; R. kikuchii n. sp. is distinguished from the four mentioned species by the different shape of the spicules. (ref. ID; 1765)

    Descriptions

    This species found in the sand of intertidal zone in Amakusa, south Japan. (ref. ID; 1765)
  • Male: Body is elongated, slender and sharply tapers is front of the amphids. The cuticle is strongly annulate; the annules are anteriorly orientated in the anterior part, and posteriorly in the posterior part of the body. The position of the reversal of orientation appears at about 54-60% of the body length, the reversal point of the dorsal side being a little posterior to that of ventral side. The body annules are decorated with one or two rows of vacuoles. Eight rows of 4-17 µm long somatic setae are present. They do not appear to be arranged in pairs, but are slightly staggered over the entire body-surface. The head bears six cephalic setae of 3 µm length, which correspond to about one head diameter. The lip region is weakly outlined, but in some specimens, there seem to be 6 lips. 32-37 annules lie between anterior end of body and anterior edge of amphid. The amphids are located just behind the base of stoma. The body diameter at the base of stoma is about 2.4 times of the width of head. The oval shaped amphids, 8-10 µm length and 6-8 µm width, are about 1.5 times longer and 1.4 times wider than those of the females (6-7 µm length and 4-6 µm width). They occupy about 84(77-88)% of the corresponding body diameter. The pharynx is cylindrical and expands a little in its posterior region. The small cardia protrudes slightly into the cylindrical intestine. The tip of the anterior testis is located at 46-51% of the body length to the left of the intestine, while the posterior one is to the right. The structure of the testes is not clear. The spicules are asymmetric. The right one is always bigger and longer than left one, having a recurved bow-like shape and a thick wall which is bent at the proximal end. The left one is notably slenderer, shorter and slightly bent in its distal part. The gubernaculum is also asymmetric and has a cuticularized postero-dorsal apophysis. Only two caudal glands are clearly observed. The tail is conical, ventrally curved, and the spinneret is terminally located. (ref. ID; 1765)
  • Female: The size of the body, structure and measurements of the various parts of the body and general form are very similar to male specimens. In contrast to males, the amphids are smaller, and the tail is slightly shorter. The reproductive system is monodelphic, prodelphic and outstretched. The reproductive system (average 126 µm long) begins anteriorly at 41-43% of body length, lies to the left of the intestine and reaches the vulva at 68-70% of the body length. The vulva is covered with a single flap. (ref. ID; 1765)

    Etymology

    This species is dedicated to Prof. Taiji Kikuchi who gave Aryuthaka the opportunity to extend his study and discover this species in Japan. (ref. ID; 1765)