Libyodrilus crassisetus, Clausen, 2004

Clausen, Martha Weis, 2004, Description of seven new species of Libyodrilus Beddard from Cameroon, with a key to the species of the genus (Oligochaeta: Eudrilidae), Journal of Natural History 38 (15), pp. 1851-1880 : 1857-1859

Libyodrilus crassisetus n. sp.

(figures 6A, 7A, 9A, B)

Material examined

Type material. Cameroon, 19 miles from Djoum , 2 ‡ 40 ’ N, 12 ‡ 34 ’ E, Djoum- Sangmelima road, muddy soil near small stream, 25 January 1966, coll. M. W. Clausen (holotype: one clitellate, ZMUC OLI-1 ; paratypes: three clitellates, five aclitellates, ZMUC OLI-2 ). Only one clitellate and one aclitellate were complete .

External characters (figure 7A)

HOLOTYPE: length 105 mm, maximum diameter 4.5 mm, 206 segments; complete clitellate paratype 92 mm long, 3 mm wide, 184 segments. Variation in diameter in other paratypes 3.0– 4.5 mm. Annulation varying a little from specimen to specimen, sometimes difficult to see due to fixation. Segments 1–4 without annulation, 5–7 tetra-annulate, 8–13 multi-annulate, segments posterior to clitellum multi-annulate, annulation disappearing towards hind end. Annulation in clitellum not visible in some fixed specimens. Prostomium prolobous. Clitellum brownish red, rest of body without pigment. Setae uniform. Setal formula: aa: ab: bc: cd ~ 6:1.3:5.8:1, dd ~ two-thirds of body circumference at segment 10; 8:1:7:1, dd ~ two-thirds of body circumference at segment 30. No normal ventral setae, but penial setae present in segment 17. Setae of segments 15 and 16 and lateral setae of 17 not distinguishable exteriorly in some specimens. Clitellum annular, with up to 4 1/3 segments in segments 1/3 14, 14–1/3 18, replaced by genital swelling in posterior half of 17 (see below).

Dorsal pores absent. Nephridiopores not discernible.

Spermarial pore unpaired, m/v in setal zone of segment 13, ca 0.3-mm-long transverse slit surrounded by circular swelling about 1/2 aa in diameter.

Female pores paired, in segment 15, 3–4 cd dorsal to d just posterior to setal zone.

Male pores: euprostates opening separately into common, transverse slit, about 1.5-mm-long, situated mid-ventrally in 17 between setal zone and 17/18. Slit located on a small cone-shaped swelling reaching setal lines a (in some specimens between a and b) in posterior half of segment 17 (all clitellate specimens; in one aclitellate a little further extended, in two a little less). Penial sacs opening into the slit just in front of and slightly lateral to openings of euprostates.

Internal characters

First septum 4/5. Septa 4/5–10/11 with thick layer of muscular fibres, septa 11/12–12/13 less muscular, remaining ones thin. Pharynx extending to 4/5. No oesophageal gizzards, ventral oesophageal sacs or paired calciferous glands. Wall of oesophagus in 11 and 12 very richly supplied with blood from supra-oesophageal vessel. Intestine beginning in segment 19. Three intestinal gizzards, one in each of 23, 24 and 25. Thin-walled sections with four pouches (two dorsally and two ventrally) anterior to gizzards in 24 and 25. Median typhlosole present from segment 24 (not in the gizzards) gradually becoming less distinct from ca segment 135. Lateral typhlosole present from segment 26, extending to 33/34 or 34/35. Small yellow pouches on septa dorsal to dorsal vessel from 20/21 to about 123/124. Segment in which they disappear varies a little from specimen to specimen. The pouches are evaginations of the septa like those in Libyodrilus mekoensis (see Clausen, 1965: 284).

Dorsal blood vessel traceable to posterior face of 5/6, doubled (but united at septal insertions) in segments 13, 14–21, 22. Supra-oesophageal vessel large and clearly visible in 6–12. Hearts in segments 6–12. Subneural vessel dividing into two extra-oesophageal vessels in segment 16.

Excretory system holonephric.

Beginning proandric reduction. One pair of testes in 10. Funnels paired in 10, ca 2 mm in diameter, white with numerous plications and white iridescence. Funnels in 11 paired; reduced, ca 0.4 mm in diameter, without plications and iridescence. Thin testis sac extending from side to side, covering testes and funnels in 10. Two pairs of seminal vesicles, in 11 well developed and restricted to segment, in 12 reduced or absent. Two pairs of vasa deferentia. Some specimens with ducts coming from segment 10 thicker than ducts coming from segment 11 and with white iridescence. Vasa deferentia entering lateral side of euprostates ca 1 mm from ectal end.

Euprostates in clitellate specimens 2.8–4.0-mm-long and 1.3–1.4-mm-thick organs situated ventrolateral to gut in 18–20. In one specimen euprostates in 18 only flexed around lateral side of gut. Ectal part of each euprostate narrowing gradually and opening by narrow duct in body wall into common slit as described above.

Sacs of penial setae situated median to ectal end of euprostates. One penial seta in each sac. Each seta (figure 6A) slightly curved, gradually tapering towards ectal end, 1.2 mm long and with maximum width of 0.08 mm. Setae partly hollow; canal gradually tapering towards inner part of curve of seta and disappearing at ca one-third of length of seta from ectal end. Growth striation clearly visible.

Spermarium (figure 9A) consisting of a median dorsal sac with two branches emerging from anterior corners of sac and embracing oesophagus and nerve cord in segment 13. The two branches meet and fuse below nerve cord before continuing into body wall in narrow duct leading to spermarial pore. In two (one clitellate and one aclitellate) of six specimens the two branches fuse between nerve cord and oesophagus, thus forming two rings, one around nerve cord and one around oesophagus, with a short tube between the two rings. Dorsal sac extending from perioesophageal ring to 16/17. No diverticula behind perioesophageal ring. Receptaculum ovorum (ovisac) (figure 9B) of each side situated in pocket of septum 13/14. Each ovisac opening into ental part of oviduct, which has overgrown funnel in 13. Duct passing through 13/14, traversing segment 14, adhering to anterior face of 14/15, and disappearing into body wall in segment 15 at level of female pores. Each ovisac connecting ventrally with perioesophageal branch of that side by a short duct. Ovaries present on posterior face of 12/ 13 in young specimens without spermarium. No ovaries observed in adults.

Remarks

Libyodrilus crassisetus belongs, together with L. tenuisetus n. sp., L. platybrachyoncus n. sp. and L. kamerunensis Michaelsen, 1915 , to spermarial group I (table 1). It is distinguishable from the three other species in that group by size and shape of penial setae (figures 6A, G–H, E and 5B, respectively) and by the possession of yellow pouches. From L. kamerunensis and L. platybrachyoncus it is most readily recognizable by the shape of the genital swellings (see figure 7A, B, D). Distribution

Only known from the type locality in southern Cameroon, 19 miles from Djoum .

Etymology The name L. crassisetus refers to the stout penial setae of the species.