Paracanthonchus macrodon ( Ditlevsen, 1918 )

Lee, Hyo Jin, Jung, Jongwoo & Rho, Hyun Soo, 2016, Two unrecorded marine nematode species of Paracanthonchus (Nematoda: Cyatholaimidae) from the East Sea of Korea, Journal of Species Research 5 (3), pp. 503-513 : 507-510

1. Paracanthonchus macrodon ( Ditlevsen, 1918)

ǖậṻṄṵệ (ṳAE)

Cyatholaimus macrodon Ditlevsen, 1918, p. 200 , figs. 6­8.

Paracanthonchus macrodon : Micoletzky, 1924, p. 138; Kito, 1978, p. 258, fig. 6.

Material examined. 5♂♂ and 3$$, Bugu­ri , Uljingun , Gyeongsangbuk­do, Korea (37°06′21.39″N, 129° 22′37.42″E), collected on 9 July 2014 by Hyo Jin Lee ; Jugwang­myeon , Goseong­gun, Gangwon­do, Korea (38°19′41.65″N, 128°31′45.63″E), collected on 2 Oct. 2014. The specimens are kept in the collection of the author. All are mounted in anhydrous glycerin between two coverslips on H­S slides, sealed with nail polish .

Measurements. See Table 1 for detailed measurements and morphometric ratios.

Description. Males: Body length 2,282 ­2,557 μm long, cylindrical, slightly tapering anterior ( Figs. 1A , 3A ). Maximum body diameter 87­104 μm. Cuticle marked homogeneously, closely arranged in transverse rows of fine punctations, starting at level of cephalic setae. Space of rows relatively narrow at mid­body region, slightly larg­ er and broader at extremities. Cuticle pore about 2 μm wide, distributed throughout body ( Figs. 1C , 3D ). Between amphideal fovea and never ring region arranged at about six rows within 10 μm; in middle of body about seven to eight rows within same distance. Lateral modified punctuations appeared throughout body, but more distinct and numerous in pharyngeal and tail region. Head with inner circle of six labial papillae about 3 μm long and outer circle of 10 (6 + 4) cephalic setae, four shorter cephalic setae 8.7­10.8 μm and six longer setae 12.3­16.1 μm, 34-44% of head diameter. Buccal cavity with prominent large dorsal tooth and two minute subventral teeth ( Figs. 1C , 3B ). Amphideal fovea ventrally wound spiral with 3.75 turns, about 32­35% of head diameter. Amphideal fovea height equal to eight to ten punctuation rows ( Figs. 1C , 3C ). Ocelli absent. Esophagus cylindrical, 359­403 μm long, slightly broadened at its base. No distinct cardia. Nerve ring encircling pharynx, situated at 46­51% of pharynx length from anterior end. Excretory pore opening located at 100.2­119.8 μm from anterior end, small ventral gland located in esophagus end ( Fig. 1B ). Cervical setae 6.7­9.5 μm long, and a few somatic setae sparsely distributed throughout body along subdorsal and subventral. Tail rather plumped, conical, with swollen tip, 178­205 μm long, about 2.4- 2.6 times of anal body diameter. Three long and stout post­cloacal setae present, anterior two setae longer than backmost setae. Cell bodies of three caudal glands situated in proximal third, subventral and subdorsal setae situated at tail region ( Figs. 1F , 3H ). Reproduction system diorchic. Spicules paired, arcuate, slightly bent at middle part and tapering distally. Gubernaculum paired, slightly shorter than spicules. Proximal portion rather sharp, and distal one­third broadening with massively enlarged distally L­shaped, distal end plate about 16­20 μm wide, with numerous cusps, and three or four large cusps ( Figs. 1E, 1F , 3E, 3G ). Six precloacal supplestretched. Vulva 1,026 ­1,179 μm from anterior end, situated at 46­48% of total body length ( Fig. 2E ). Tail short anal body diameter ( Fig. 2C ).

Remark. In 1918, Ditlevsen reported the species Cyatholaimus macrodon Ditlevsen, 1918 from Oresund in Danish belt Sea. Thereafter, Micoletzky erected the genus Paracanthonchus with 5 species including P a r a c a n t h o n c h u s m a c ro d o n (D i t l e v s e n, 1 9 1 8). Paracanthonchus macrodon has been previously report­ ed from Europe, America and Japan Sea. The present Korean specimens were discovered from the seagrass bed of intertidal rocky shore of the East Sea, Korea. Paracanthonchus macrodon is distinguished from its congeners in having the cuticular differentiation, strongly dilated gubernaculum with numerous cusps, presence of three post­cloacal setae, and arrangement of six (4 + 2) precloacal supplement. The present specimens resemble P. hartogi Inglis, 1970 , P. parahartogi Decraemer and Coomans, 1978 , P. stekohveni Wieser, 1954 and P. sunesoni (Allgen, 1942) , mainly in possessing six precloacal supplements and a more or less pronounced L­shaped gubernaculum with a large, spiny distal part in lateral view. Paracanthonchus macrodon is clearly distinguished from P. stekhoveni and P. sunesoni by arrangement of precloacal suppelements. Distance of among the four precloacal supplements is almost equal in P. stekhoveni and P. sunesoni , but distance of anteriormost and second supplement is longer than other adjacent supplements in P. macrodon . Paracanthonchus hartogi has a fine striation cuticle without lateral differentiation, whereas P. macrodon has fine punctuations and lateral differentiation. Moreover, P. macrodon has long and stout three postcloacal setae, but P. parahartogi dosen’t have postcloacal setae. The present Korean specimens are very similar with the original description by Ditlevsen 1918, except for position of the excretory pore (100.2­119.8 μm vs. 18 μm from anterior end), turns of amphideal fovea (3.75 vs. 2.5 turns) and number of precloacal supplements (six vs. four). The Korean specimens are closely related to P. macrodon reported from subtidal zone in the coasts of Oshoro, Japan by Kito (1978) in general features. However, Korean specimens are not accorded by distance of among anterior four precloacal supplements (50 μm, 26 μm, 25 μm vs. 35 μm, 11 μm, 24 μm respectively).

Figures

Fig. 1. Paracanthonchus macrodon, male, lateral view.A, total body; B, anterior body region; C, fine punctations of cuticle region; D, head region; E, spicules with gubernaculum; F, tail region; G, cloacal region. Scale bars:A=100μm, B, F, G=50μm, C-E=20μm.

Fig. 3. Paracanthonchus macrodon, DIC photomicrographs, male, lateral view. A, habitus; B, head region; C, amphideal fovea; D, cuticle on the anterior region; E, spicule with gubernaculums; F, pre­cloacal supplement; G, post­cloacal setae; H, tail region. Scale bars: A=100 μm, B-H=10μm.

Fig. 2. Paracanthonchus macrodon, female, lateral view.A, total body; B, head region; C, tail region; D, anterior body region; E, reproductive system. Scale bars:A=100μm, B, C=20 μm, D, E=50 μm.