Diplotrema oaxacana, Fragoso & Rojas, 2019

Fragoso, Carlos & Rojas, Patricia, 2019, More new Diplotrema earthworm species from southern Mexico (Annelida, Crassiclitellata, Acanthodrilidae, Acanthodrilinae), Zootaxa 4688 (4), pp. 483-502 : 485-489

Diplotrema oaxacana sp. nov.

( Figures 1, 2, 3, 4)

urn:lsid:zoobank.org:act:122E50F7-E656-473F-A7D9-E9

Diplotrema zilchi ( Graff, 1957) , sensu Fragoso 1993: 37, 2001: 163, 2007: 122, Fragoso et al. 1995: 111; non Graff.

Localities and material. Mexico, Oaxaca state: 1) Highway 175 on the road to Tuxtepec, 23 km from Oaxaca city, close to deviation to the village of Santa Catarina Ixtepeji, municipality of Santa Catarina Ixtepeji , pine-oak for- est on an west slope of 45°, at 0–20 cm soil depth, 17°13’42.3’’N, 96°34’25.2’’W, 2460 m asl, one clitellate adult 08/30/1991, C. Fragoso and P. Rojas; 2) Highway 175 on the road to Tuxtepec, 18 km after the town of Guelatao, municipality of San Juan Atepec, pine-oak forest at 0–10 cm soil depth, 17°24’19.12’’N, 96°30’46.47’’W, 2740 m asl, three clitellate adults 08/30/1991, C. Fragoso and P. Rojas. ( Fig. 10) .

Holotype. Clitellate adult from locality 1: IEOL 3103 .

Paratypes. Three entire clitellate adults from locality 2: IEOL 3102 , 3262 and 4846 .

Description. External. Length 25–37 mm (average 30.6, n=4); holotype 30 mm. Width, middle body: 1.33– 1.55 mm (average=1.42, n=4); holotype 1.4 mm. Number of segments 74–81 (average=78, n=4); holotype 74 segments. Secondary annulation characterized by several furrows: before clitellum one presetal and one or two postsetal; after clitellum two presetal and two or three postsetal. Middle segments 2.4–3.2 times wider than long ( Fig. 1A,B); last segments 2.3–3.8 times wider than long. Pigment absent. Prostomium open epilobous ( Fig. 1D). Setae eight per segment, visible from 2; closely paired throughout ( Fig. 1A,B)). Setal formula (averages, n=4) (aa:ab: bc:cd:dd) at 10: 6.9:1:7.5:0.8:29 and 1.15 dd =1/2 C; at 30: 9.8:1:7.7:1.1:26.9 and 0.92 dd =1/2 C; ten segments before anus: 7.6:1:5.6:1:23 and 1 dd =1/2 C.

Very thin (width 6.17, 6.25 μm) and long (2.5, 3.0 mm) paired hair-like penial setae (a and b) in 17 and 19; they are smooth, without any ornamentation ( Fig. 4B), curved in some of their extension, and with the distal part irregularly undulated ( Fig. 4C). In some individuals these setae were externally visible ( Fig. 1A); internally each seta a and b contained within long follicles that are attached to lateral-dorsal body wall ( Fig. 2B). Bundles of 17 and 19 run independently until segment 20, where they are fixed together by connective tissue. Genital (spermathecal or copulatory) setae present in segments 8 and 9. They are slightly curved, with irregular notch ornamentation limited to ectal half and with a lanceolate non-ornamented apex ( Fig. 4A). Both setae a and b with similar shape and dimensions (length: 296–319 μm; width: 6.55–8.7 μm).

Clitellum saddle shaped in 1/2 13, 14–17, 3/4 18 (4 to 5 segments); orange to vermilion color, reaching slightly outside B ( Fig. 1 A–C). Dorsal pores present, first functional pore in 10/11 (2 ind.) or 11/12 (1 ind.); in 9/10 visible in two individuals, but closed. Paired minute spermathecal pores difficult to see externally in the majority of individuals (but visible in the holotype, Fig. 1A) and located in AB of 7/8 and 8/9. Female pores in 14, presetal, in or slightly outside B. Two pairs of prostatic pores in A or AB of segments 17 and 19, joined by almost straight and faint seminal grooves which run slightly outside AB ( Fig. 1A,B). Male pores not seen, probably within seminal grooves and, as deduced from male gonoduct, opening in segment 18. Genital marks as swellings and papillae. Paired swellings in AB or slightly outside B in segments 8 and 9 (in one individual also in 7), indicating the presence of genital setae. Number and location of single and paired papillae variable according to individuals, but all ovoid or quadrangular shaped and with a smaller and central tumescence. Holotype with ovoid mid-ventral papillae in 11/12 and with quadrangular, paired, almost fused papillae in 12/13, 16/17, 19/20 and 20/21 and extending in B–B ( Fig. 1A); B–B body wall of 20 and 21 slightly thickened. In the other examined individuals, midventral papillae in 9/10, 10/11 or 10/11, 13/14, 14/15 and 15/16 with single or paired central tumescences; paired non-united papillae extending in A–A or B–B in some of intersegments 15/16 – 20/21 ( Fig. 1B,C).

Internal. Septa 5/6 thin and membranous; 6/7–9/10 slightly muscular; 10/11, 11/12 more muscular; 12/13, 13/14 clearly muscular in the holotype, and thinner in paratypes; all former septa funnel shaped. One large gizzard in 5, square or cylindrical shaped. Gizzard dimensions (length by width): 0.92 by 0.86 mm (holotype), 0.81 by 0.84 mm, and 0.92 by 0.69 mm. Esophagus tubular, without dilatations; in 8–11 presence of internal lamellae, the ventral pair more conspicuous than the lateral pairs; in segments 12 and 13 lumen highly occluded by lamellae, representing 16% of esophagus diameter. Intestine starting in 13/14 (holotype and one paratype) or 14/15 (two paratypes). Laminar, dorsal typhlosole starting abruptly in 15, reaching maximal size after one or two segments, ending 21 (holotype; segment 53, covering 38 segments) or 24 segments (segments 54, 56, 57; covering 39, 41, 42 segments, respectively) before anus.

Dorsal vessel visible throughout; in two individuals apparently double over the intestine ( Fig. 2A). Supraesophageal vessel visible in segments 11–12. Lateral hearts in 10; latero-esophageal hearts in 11 and 12. Ventral vessel present. Ventro-lateral infra- esophageal vessels conspicuous in segments 7–12 (paratype IEOL 3262) or 16–18 (IEOL 3102). Nephridial system holoic, avesiculate, exonephric, apparently stomate and parietal; in segments anterior to 10 closer to ventral midline ( Fig. 2B). Nephrostomes and nephropores not seen. Male apparatus holandric. Iridiscent male funnels and testes in 10 and 11; funnels larger in 11; in one individual testes and funnels connected by abundant coagulum. Male gonoduct double, straight, running on body wall of segments 13–18 and slightly outside B, entering body wall in 17 or the equator of 18. Two pairs of acinous, dorso-lateral seminal vesicles in 11 and 12 (11 <12). Two pairs of coiled tubular prostates in 17 and 19 ( Fig. 2B), limited to the respective segments or extending one segment forwards and one backwards; muscular ducts transversely located in 17 and 19; glandular parts of prostates two times thicker and three-four times longer than the muscular duct.

Paired shrub ovaries and female funnels in 13. Ovules clearly seen; female funnels ventral, near to 13/14, and not very close to mid-ventral line. Paired spermathecae in 8 and 9, opening in 7/8 and 8/9 respectively, and fixed by connective tissue to the floor and septa; ampulla joining duct at right angle, diverticulum joining duct along the same axis ( Fig. 3). Ampullae of posterior segment (s. 9) ( Fig. 3B,F) wider and less or equally elongate than anterior ones (s. 8) ( Fig. 3A,C,D,E); diverticulum of about equal length as ampulla or longer (1.3, 1.9, 2.8 times). Maximal total length of spermatheca: 0.82, 0.87 mm (paratype IEOL 3102; Fig. 3A,B) and 0.93 mm (paratype IEOL 3262; Fig. 3F).

Etymology. The name of the species refers to the Mexican state where all individuals of this new species were found.

Remarks. D. oaxacana sp. nov. is separated from all neotropical Diplotrema species ( Table 1 of Fragoso & Rojas 2018) by the presence of spermathecal setae in combination with an ampulla that is transversally connected. By this last character the new species relates to D. chajulensis , D. jenniferae , D. murchiei and D. oxcutzcabensis , being separated from all by the presence of spermathecal setae. D. oaxacana sp. nov. clearly differs from other species with spermathecal setae ( D. papillata and D. ulrici ) by the location and number of seminal vesicles (two pairs in segments 11 and 12 in D. oaxacana sp. nov. vs. two pairs in 9 and 12 in D. papillata and one pair in 11 in D. ulrici ). The present type material of the new species has previously been identified as Diplotrema zilchi ( Graff, 1957) by Fragoso (1993, 2001, 2007) and Fragoso et al. (1995), based on the elongate diverticulum longer than the ampulla; both species, however, are separated by the genital setae (present in D. oaxacana sp. nov. vs. absent in D. zilchi ), the shape of penial setae (hair-like with undulated distal regions vs. straight with a thorny distal region) and the beginning of typhlosole (in segment 15 vs. segment 20). Hence, D. zilchi remains a singleton species restricted to the southwestern mountains of El Salvador.