Desmoscolex Claparède, 1863

Rho, H. S., Kim, W. & Chang, C. Y., 2007, Description of two new free-living marine nematode species of the subgenus Desmolorenzenia (Desmoscolecida, genus Desmoscolex) from Korea, Journal of Natural History 41 (5 - 8), pp. 313-326 : 319-323

Genus Desmoscolex Claparède, 1863

Subgenus Desmolorenzenia Freudenhammer, 1975 Desmoscolex (Desmolorenzenia) pedunculus sp. nov.

( Figures 4–6 )

Type material

Holotype male ( RIT701 ) and one paratype female ( RIT702 ), mounted in glycerine on H-S slide, are deposited in the nematode collection of the Royal Belgian Institute of Natural Sciences, Brussels, Belgium. Two paratypes (one male and one female) (DB30005, 30006) are deposited in the nematode collection of the Department of Biology , Daegu University , Korea. Another two paratypes (one male and one juvenile) (SNU10011, 10012) are kept in the first author’s (H. S. Rho) research collection at the School of Biological Sciences , Seoul National University, Korea.

Type locality

Geumjin, Youngdeok (36 u 219560 N, 129 u 239400 E), collected on 26 September 1998 by H. S. Rho and J. W. Choi.

Type habitats

The nematodes were obtained from shallow subtidal invertebrates (sponges, bryozoans, and polychaetes), which were collected from depths of 3 to 5 m by scuba diving.

Etymology

The specific name, pedunculus , refers to the well-developed peduncles of insertion of both subdorsal and subventral somatic setae.

Measurements

Holotype male: L5290; hd521; cs519; sd 1518; sd 3517; sd 7513; sd 9513; sd 13515; sd 16515; sd 17523; sv 2511; sv 4512; sv 6512; sv 8514; sv 10514; sv 12513; sv 14515; sv 15513; ph559; t562; tmr539; tmrw516; mbd552; mbde547; spic526; gub57; a55.7; b54.9; c54.7.

Paratype male (n 51): L5470; hd523; cs524; sd 1522; sd 3521; sd 5521; sd 7520; sd 9520; sd 11520; sd 13520; sd 16519; sd 17526; sv 2513; sv 4515; sv 6516; sv 8517; sv 10514; sv 12517; sv 14516; ph595; t588; tmr553; tmrw521; mbd553; mbde547; spic529; gub58; c55.3.

Paratype females (n 53): L5355–420 (398); hd523–25; cs515–18; sd 1517; sd 3515 – 16; sd 5513 –16; sd 7515 –17; sd 9517 –19; sd 11517 –19; sd 13517 –18; sd 16516 –21; sd 17524 –27; sv 2513 –14; sv 4513; sv 6513 –15; sv 8513; sv 10515; sv 12515; sv 14513 –15; sv 15515; ph573–75; t564–74; tmr543–50; tmrw524–26; mbd555–65; mbde545–58; V%550; a56.5–6.9; b54.9–5.6; c55.6.

Description

Males. Body small, ventrally curved, slightly tapered anteriorly and posteriorly; cuticle with 17 broad desmens ( Figures 4A , 5A, B ). Desmen quadricomoid with inversion in orientation at level of desmen 14 ( Figure 6B–D ). Each desmen covered with layer of secretion and finely granular foreign material.

Somatic setae ( Figure 4A ) arranged according to typical desmoscolecid setal pattern: nine pairs of subdorsal somatic setae on desmens 1, 3, 5, 7, 9, 11, 13, 16, 17; eight pairs of subventral somatic setae on desmens 2, 4, 6, 8, 10, 12, 14, 15. Subdorsal somatic setae ( Figure 4A, B ) gradually becoming finer to an open tip, with fine mid-central canal, longer than subventral somatic setae, and inserted on peduncle. Anteriormost and posteriormost pair of subdorsal somatic setae slightly elongate compared to other setae. Subventral somatic setae ( Figure 4A ) small and relatively slender, inserted on peduncle; cylindrical basal part broad, with fine mid-central canal, tapered to open tip. Subventral somatic setae all about same length, except for those on desmen 14, which are slightly longer.

Head globular, wider than long, anteriorly tapered and truncated, and posteriorly with more or less cylindrical neck-region ( Figures 4A, B , 5A , 6A ). Cephalic cuticle completely covered with thin layer of fine granular desmos, except in amphideal zone. Labial region ( Figures 4B , 5C, D ) hexagonal, offset with separate lips. Circle of six minute, papilliform labial sensilla situated near edge of oral aperture ( Figure 5C ). Specialized cephalic tubercles situated between cephalic tubercles and labial sensilla. Elliptical cephalic tubercles arranged in single crown near labial sensilla. Outer margin of lip region surrounded by well-developed cephalic ridge. Cephalic setae ( Figure 4A, B ) tapering distally, 19 mm in length, shorter than head width. Cephalic setae jointed distally, i.e. finer distal part socketed into broad, cylindrical basal part near the tip of setae ( Figures 4B, E , 5C, D ), inserted on peduncles just anterior to mid-head. Amphideal fovea ( Figure 4B ) rounded, largely covering head laterally, situated at level of mid-head.

Digestive system typical of Desmolorenzenia . Buccal opening with minute buccal cavity. Oesophagus 59 mm long, posteriorly extending to level of posterior margin of desmen 3 ( Figure 4A ); intestine dorsal to reproductive system. Ocelli not observed. Reproductive system typical of Desmoscolecidae : single outstretched testis, extending up to level between desmens 6 and 7 ( Figure 4A ). Ejaculatory glands not observed. Spicules relatively short (26 mm long) ( Figure 4A, C ), nearly straight; blade tapering caudally to pointed tip, proximally provided with well-developed offset capitulum. Gubernaculum thin, troughshaped, 6 mm long, adjacent to tip of spicules. Cloacal tube broad, clearly protruding from medioventral body wall in desmen 15 ( Figure 4A, C ).

Tail with two desmens ( Figure 4A ). End ring 39 mm long, about 2.4 times longer than wide, consisting of broad cylindrical anterior part extending up to insertion of terminal subdorsal somatic setae, and ventrally bent terminal part, tapering towards well-developed naked spinneret. End ring, with exception of terminal spinneret, totally covered with desmos. Caudal glands not observed.

Females. Similar to males in most respects ( Figure 4D ). Body cuticle ( Figure 4E ) with 17 desmens. Somatic setae ( Figure 4D ) arranged according to typical desmoscolecid setal pattern: nine pairs of subdorsal setae on desmens 1, 3, 5, 7, 9, 11, 13, 16, 17; eight pairs of subventral setae on desmens 2, 4, 6, 8, 10, 12, 14, 15. Amphideal fovea ( Figure 4E ) rounded (14 mm long), largely covering head laterally, situated on anterior part of head capsule. Reproductive system didelphic–amphidelphic with both branches outstretched, situated ventrally to intestine, between desmens 7 and 13. Vulva situated between desmens 10 and 11 ( Figure 4D ). Anal tube not protruded at all, situated between desmens 15 and 16 ( Figure 4D ). Tail with two desmens ( Figure 4D ). End ring 50 mm long, about 1.9 times longer than wide.

Diagnosis

Desmoscolex (Desmolorenzenia) pedunculus sp. nov. is mainly characterized by the following combination of characters: (1) presence of 17 desmens with inversing desmen 14 and typical desmoscolecid setal pattern (nine pairs of subdorsal somatic setae and eight pairs of subventral somatic setae); (2) globular head with well-developed lip region, provided with six minute labial sensilla; (3) hexagonal cephalic ridge and numerous cephalic tubercles surrounding lip region; (4) cephalic setae jointed at their distal part; (5) presence of peduncle for both subdorsal and subventral somatic setae; and (6) end ring with broad, cylindrical anterior part, extending up to insertion of posteriormost subdorsal somatic setae, and ventrally bent terminal part tapering towards a well-developed naked spinneret.

For differential diagnosis, see Discussion.

Figures

Figure 4. Desmoscolex (Desmolorenzenia) pedunculus sp. nov. (A–C) Holotype male: (A) habitus (subdorsal setae on desmens 5 and 11 left side are broken off); (B) head region, right side in surface view; (C) copulatory apparatus, left side in optical section. (D, E) Allotype female: (D) habitus; (E) head region, left side in surface view. Scale bars: 50 mm (A, D); 20 mm (B, E); 10 mm (C).

Figure 5. Desmoscolex (Desmolorenzenia) pedunculus sp. nov., paratype male (SEM micrographs). (A) Habitus, lateral view; (B) habitus, oblique lateral view; (C) head, en face view; (D) head region, right side. Scale bars: 60 mm (A); 40 mm (B); 10 mm (C, D).

Figure 6. Desmoscolex (Desmolorenzenia) pedunculus sp. nov., paratype male (SEM micrographs). (A) Head region, right side; (B) detail of body wall at the level of desmens 4–6, right side; (C) detail of body wall at the level of desmens 13–15, right side; (D) posterior body region, right side. Scale bars: 10 mm (A); 20 mm (B, C); 30 mm (D).