Petroscolex centenarius Csuzdi, Szederjesi & Sherlock

Csuzdi, Csaba, Rota, Emilia, Szederjesi, Tímea, Sherlock, Emma, Brown, George G., Chang, Chih-Han, Cosin, Dario Diaz, Fragoso, Carlos, Jamieson, Barrie G. M., Hong, Yong, James, Samuel W., Paoletti, Maurizio G., Pavlícek, Tomás, Plisko, Danuta, Pop, Victor V. & Shen, Huei-Ping, 2019, Description of a new Central African earthworm, Petroscolex centenarius gen et sp. nov. (Crassiclitellata, Eudrilidae), celebrating the 100 th birthday of Pietro Omodeo, Zootaxa 4674 (5), pp. 501-508 : 504-507

Petroscolex centenarius Csuzdi, Szederjesi & Sherlock , sp. nov.

( Figures 2 , 3 )

Holotype. NHMUK 1997.1594 clitellate adult. DR Congo, Kivu, Irangi. Leg. Gazana N’Doli, 20.02.1973.

Paratypes. HNHM AF/3555 1 ex. clitellate adult , NHMUK 1997.1595 1 ex. clitellate adult broken in two pieces. Locality and date same as of the Holotype. NHMUK 1997.1548 – 1549 1 ex. clitellate adult, 1 ex. juvenile, HNHM AF/3539 1 ex. clitellate adult, DR Congo, Kivu, Irangi. Leg. Gazana N’Doli, 08.03.1973. NHMUK 1997.1526 – 1529 1 ex. clitellate adult, 1 ex. aclitellate adult, 2 ex. juvenile, NHMUK ANEA 2019.7368 1 ex. clitellate adult, HNHM AF/5754 1 ex. clitellate adult, DR Congo, Kivu, Irangi. Leg. Gazana N’Doli, 09.03.1973. NHMUK 1997.1530 1 ex. aclitellate adult, DR Congo, Kivu, Irangi. Leg. Gazana N’Doli, 07.06.1973 .

Etymology. The specific epithet refers to the 100th birthday of Prof. Pietro Omodeo.

Description. Holotype: Preserved length 160 mm, diameter after clitellum 5 mm, segment number 196. Paratypes: 150–190 mm in length, 4–5 mm in diameter. Segment number 153–206, anteclitellar segments frequently multiannulate, segments ii–xi carinate. Colour preserved brownish, alive unknown. Head epilobous 1/2 open, dorsal pores lacking. Setae: ab distant cd paired, setal ratio after clitellum aa:ab:bc:cd:dd = 4:3:3.6:1:12. Nephridial pores begin on segment ii, aligned somewhat dorsal to setal line c.

Clitellum annular on segments ½xiii–½xvii. Prostatic pore midventral on a spherical papilla in xiii, near to the 12/13 intersegmental furrow which sometimes emerges as a penis-like organ. Female pores small dots on xiv, close to the intersegmental furrow 14/15 just below setal line d. Spermathecal pore single midventral on xviii ( Fig. 2 A–C).

Internal characters: Muscular gizzard in vi, large, cylindrical. Septa 7/8–10/11 moderately, 11/12 slightly thickened. Calciferous glands paired in xiv, large mouflon-horn shaped. Small chylus-sacs in ix, x, xi. Dorsal blood vessel simple throughout. Hearts in x–xi, moniliform. Nephridial system holoic with thin biramous nephridial bladders. Typhlosole lacking.

Proandric. Testes and sperm funnels in x enclosed in a coiled sperm-reservoir. Seminal vesicles large in xi. Ovaries in xiii enclosed in an ovarian capsule pendant from septum 12/13. This ovarian capsule laterally continuing in a short, hardly recognizable ovarian duct joining the fertilisation chamber and bearing a pendant ovisac. From the fertilisation chamber a straight oviduct leads to the female pore in xiv. The ovarian capsule medially communicates on both sides with a delicate ovo-spermathecal duct running alongside the bursa copulatrix and joining apically to the pear-shaped, highly muscular spermathecal atrium ( Fig. 3A ). This atrium opens midventrally on segment xviii. The left and right ovarian apparatus connected by a small intercommunicating duct running above the intestine ( Fig. 3A ).

Prostates a pair of long spiral tubes, joining the bursa copulatrix (copulation pouch) via a common Y-shaped duct. Bursa copulatrix situated above the spermathecal atrium and completely covers it dorsally. Bursa copulatrix highly muscular, somewhat spindle-shaped, oriented headwards and opening (through the prostatic pore) on a penislike protuberance on xiii (usually retracted). The two male ducts run backward along both sides of this copulatory pouch, and join to it subapically near each other ( Fig. 3B ). Penial setae lacking.

Discussion. Eudrilidae is the only earthworm family with internal fertilisation ( Clausen 1965; Jamieson 1967; Sims 1969), which requires intercommunication of the ovarial and spermathecal systems resulting in a common ovo-spermathecal apparatus. This ovo-spermathecal apparatus is highly variable among different taxa both in its structure and external opening ( Sims 1987).

The external opening of the spermatheca, usually located near the front of the clitellum, is frequently shifted back: for example, in Beddardiella Michaelsen, 1910 (spermathecal pore at 16/17), Keffia Clausen, 1963 (in xix), or in Parapolytoreutus Segun, 1980 (as far back as segment 22/23). Sometimes it shows wide variation even inside a genus: for example, in Buettneriodrilus aequatorialis Michaelsen, 1935 the spermathecal pore is in 12/13, while in Buettneriodrilus armatus (Michaelsen, 1913) it is in segment xix ( Zicsi & Csuzdi 1986; Sims 1987). The position of the prostate pores is less variable; in the genera within the family described to date, it can be found in xvii, 17/18 or in xviii. Petroscolex gen. nov. is the first genus in Eudrilidae with prostatic pore in xiii, anterior to the clitellum.

The new genus is also unique in the position of calciferous glands in xiv, not xii or xiii as in other species of the subfamily. Sims (1987) distinguished two groups of genera based on this character, one group with calciferous glands in xii, distributed in West Africa, and another one with calciferous glands in xiii, distributed across tropical Africa. Petroscolex gen. nov. with its calciferous glands in segment xiv is more similar to the latter group because all the genera with backward shifted spermathecal pores possess calciferous glands in xiii. The distribution of the new genus supports this as well, the type locality Irangi, Kivu is at the eastern border of the Congo-basin.

A third peculiarity of the new species is the proandric condition of the testes. In Eudrilidae the male apparatus is mostly holandric, although a few genera show metandric reduction: Metascolex Michaelsen, 1903 , Polytoreutus Michaelsen, 1890 or Okudrilus Csuzdi & Sherlock, 2015 . Petroscolex gen. nov. is the first eudrilid genus with proandric reduction.

Figures

FIGURE 2. Petroscolex centenarius sp. nov., photographs of type material. A. Holotype, complete worm, ventral view. B. Details of A, enlarged. C. Paratype NHMUK 1997.1595, ventral view, anterior body end. pe = penis (=everted bursa copulatrix); prp = prostatic pore; stp = spermathecal pore. Scale bar = 1 mm.

FIGURE 3. Petroscolex centenarius sp. nov., reproductive organs. A. Ovo-spermathecal system. B. Prostates with bursa copulatrix. Note that the structure shown in B is situated dorsally of that shown in A. bc = bursa copulatrix; fc = fertilisation chamber; icd = intercommunicating duct; md = male duct; od = oviduct; os = ovisac; ov = ovarium; ovd = ovo-spermathecal duct; pr = prostate; spa = spermathecal atrium.