Lacandodrilus paludosus Fragoso & Rojas, 2023

Fragoso, Carlos & Rojas, Patricia, 2023, A new semiaquatic worm (Annelida, Oligochaeta) from southeastern Mexican tropical rain forests, Zootaxa 5255 (1), pp. 136-156 : 139-147

Lacandodrilus paludosus Fragoso & Rojas sp. nov.

Figures (1, 2, 3, 4, 5, 6,7)

Localities and material. Mexico, Chiapas, Chajul village, municipality of Marques de Comillas, 1 km south of town, close to the water tank. A patch of small palms ( Bactris balanoidea and B. trichofila ) within a tropical rain forest over semi-inundated gley soils at 30–40 cm depth, 16°06'24"N, 90°55'24"W, 190 m asl ( Figure 8 ), one clitellate adult, three non-clitellate adults, two juveniles 12/30/1982, C. Fragoso.

Holotype. Fragmented clitellate adult: IEOL 3190 .

Paratypes. Three entire semi-adults with some internal genitalia: IEOL 2312 , 6565 , 6567 ; two juveniles : IEOL 6566 , 6568 .

Description. External. Dimensions: Length 50, 50, 58 mm (average= 53, n=3), holotype 28 mm (fragmented, only anterior half; Fig 1A ). Width, middle body: 0.46, 0.50, 0.64, 0.64 mm (average= 0.56, n= 4); holotype = 0.48 mm. Number of segments: 208, 225, 248 (average= 227, n= 3). Furrows: One pre- and one post-setal along all the body; in some individuals up to two pre- and two post-setal in some segments. Pigment: Absent. Prostomium; Prolobic. Setae: Eight per segment, present from segment 2 ( Fig. 1A ); closely paired throughout. Setae of preclitellar segments, conspicuous and with replacements. Setae a and b of preclitellar segments measuring 130–150 µm length, almost straight, slightly bent distally and with a slight nodulus close to its basal end; apex smooth and without ornamentations ( Fig 2A, 2B ). Setae a,b of segments 11 and 12 larger, but with the same shape of anterior ones; replacement setae measuring 64, 93 µm ( Fig. 2A, 2B ); seta c (112 µm) and d smaller than seta a and b. After clitellum all setae similar (slightly curved and without ornamentations) measuring 105 –117 microns. Setal formula (averages, n=6, relative to ab; d’d’ absolute) (aa:ab:bc:cd:dd) at 10: 3.7:1:4.7:0.9:9.2 and 0.54 d’d’ =1/2C (= cd dorsal); at 30: 5.7:1:5.3:1:14.2 and 0.7 d’d’ =1/2C (= cd slightly dorsal); ten segments before anus (only entire individuals): 2.9:1:2.4:1:14.4 and 1.2 d’d’ =1/2C (= cd ventral).

Clitellum: Annular, from ½ 12 – ½ 16, very thin ( Fig. 1A ). Dorsal pores: absent. Spermathecal pores: not visible. Female pores: In 14, presetal in AB. Male pores: In two aclitellate individuals (Paratypes IEOL 6565, 6567; Fig 1C, 1D ) it was observed from the outside, a thin band running throughout segment 11 in BC, which is assumed that corresponds to the gonoduct from male funnels of 10. In these two individuals and in the clitellate holotype (3190) ( Figs 1B, 1C, 1D ) a more thick, clearly visible and slightly undulating band of cream color was also observed extending throughout segments 12 – ¾ 13, in BC, which corresponds to male gonoducts from the male funnels of 10 and 11, that run together. If male pores are located at the end of this duct, then they are in segment 13, postsetal and in BC. Genital marks: None, only setae ab of segment 15 enclosed within small and barely visible protuberances (seen only in the clitellate holotype). Nephridial pores: not visible. Lateral bands: In all non clitellated individuals (paratypes IEOL 2312, 6565, 6566, 6567, 6568) lateral bands were observed in BC close to C, from segments 2 or 3 to segments 14, 16 or 20; in one individual they enclosed CD and were observed in more posterior segments. They are seen as depressions of external cuticle, and probably correspond to longitudinal muscle layers.

Internal ( Fig. 3A, B ). Septa: All thin and membranous. Septal glands: In segments 5, 6, 7, 8 and 9 (in 10 incipient) a kind of paired glands were observed in dorsolateral walls, attached to corresponding posterior septum ( Fig. 3B , 4A, 4B ). They were profusely mixed with lateral vascular commissures. Gizzard, Caeca and Typhlosole: Absent. Esophagus: Moniliform, with the same structure along all the body; even that no distinction in the transition to intestine was observed, in one individual and from segment 11 backwards there was an increase in length of the digestive tract in each segment ( Fig. 3B ).

Dorsal vessel: Single, visible throughout ( Fig. 3B , 4 , 5 ); in one individual size increases from segment 14 backwards.Vascular commissures: Long and contorted vessels are observed in segments 5?, 6–11; they are embedded with septal glands ( Fig. 5A ). Ventral vessel: Present. Nephridia: Ventral holonephridia observed from segment 11 backwards. They are covered by a granular peritoneal layer that gives them an ovoid, flat appearance ( Fig. 5B, C, D ); this ovoid portion is free, floating in the coelom, and not attached to septa. Nephridia gradually increase in size and from segment 15 they attain its maximal size. They are exonephric ( Fig. 5C ) (opening in ab) and probably open (stomate), even though nephrostomes were not seen. Testicles and male funnels: Holandric. Iridescent male funnels in 10 and 11; those of 11 bigger than those of 10 ( Fig 3B , 6A ); testes not seen. Both funnels are enclosed by seminal vesicles. Male gonoduct: A gonoduct that comes from male funnels of s. 10 enters the body wall in 11, very close to 10/11; a second gonoduct coming from s. 11 funnels, enters the body wall in 12, very close to 11/12. Both male conducts run intraparietal over segments 11, 12 and 3/4 of segment 13 (deduced from the external observed, undulating cream band) ( Fig. 1 B, C, D ). Accordingly, the male pore would be in 13, postsetal and in BC.

Seminal vesicles: In the clitellate holotype (IEOL 3190) and one semiadult paratype (IEOL 6565), there is one pair of sausage-shaped vesicles in segment 11; these vesicles contain male funnels, project in posterior direction from segment 12 until segments 18 or 20 and run dorso-lateral of the digestive tract, completely covering it ( Fig 3A ). In segment 10 there is another pair of vesicles that also contain male funnels, that run in anterior direction before they turn over 180° and which, apparently, are limited to the following segment 11. In a semiadult, we observed dense seminal coagulum in segments 11 and 12 that could be incipient seminal vesicles; they completely covered the esophagus. Genital glands: Two pairs of lobulate, rosette-shaped glands lie internally on the ventral body wall of segments 13 and 14 ( Fig 3 , 6 ), the anterior being the larger one. They are composed of several short lobules almost fixed to the ventral wall; they could be the equivalent of prostatic glands found in other crassiclitellate worms. We were unable to see any intraparietal connection with male gonoduct. They are superficially like the septal glands present in the anterior segments. No tubular, atrium-like glands were present.

Ovaries and female funnels: Large ovaries in segment 13 projecting from the ventral portion of 12/13 at AB row level, and extending over the entire segment ( Fig 6B , 7A ). No strings of oocytes or mature ovules were observed. In one individual the ovaries presented a large neck with a kind of developing eggs in the distal part. Female funnels on the ventral wall of segment 13 very close to 13/14, in AB, and with a duct opening in segment 14 before seta ab. Ovisacs: Apparently the septum 13/14 is modified as dorsolateral paired sacs that contain the corresponding seminal vesicles of 11, and that extends backwards until segments 18 or 20 ( Fig. 3A ). No oocytes were observed within the posterior end of these membranous sacs. Spermathecae: One pair of spermathecae without diverticulum in segment 10 ( Fig. 3A , 7B ) opening ventrally in 9/10, at AB. In the holotype the left spermatheca was empty. Conversely, the right spermatheca presented iridescence near the union with duct ( Fig 7B ) and was completely covered by the seminal vesicles and fixed to male funnels. The duct of this spermatheca turned out 180° to connect with a sausage-shaped ampulla. Width and length of ampulla was twofold and shorter than, respectively, width and length of duct. Total length of spermathecae was 580 µm (probably more, as the duct was not complete), 370 µm of this corresponding to ampulla, and 210 µm to duct.

Etymology: The name refers to the swampy habitat of the species.

Ecology: This species, considered as gen.nov.sp.nov.4 by Fragoso & Lavelle (1987), inhabited only the swampy gley soils of tropical rain forest at the Lacandon region. It was found at 40 cm depth in flooded, sandy soils, characterized by its acidity (pH=4.5), and low values of organic matter (0.9%), Ca (2.32 meq/ 100g) and Mg (0.72 meq/ 100g), and with an increase of clay in deep strata. The site was dominated by the palms Bactris balanoidea and Bactris trichofila . All the individuals were found in a single sample in the month of December. Abundance and biomass at the entire forest were very low, less than one individual by square meter ( Fragoso & Lavelle 1987); however, if only samples taken in gley soils are considered, the average abundance is higher (1.6 ind/m2).

Figures

FIGURE 1. Lacandodrilus paludosus gen. et sp. nov. External. Anterior region. Holotype IEOL 3190 A. Ventral view, segments 1–18. B. Ventral view, segments 11–14. C. Paratype IEOL 6567, ventro-lateral view of segments 10–15. D. Paratype IEOL 6565, lateral view of segments 10–15. Arrows indicate the external band that corresponds to internal male gonoducts. Letters indicate the corresponding ventral (a, b) or lateral (c, d) setae. Scale 0.5 mm.

FIGURE 2. Lacandodrilus paludosus gen. et sp. nov. A. Holotype IEOL 3190, setae a with a replacement seta from segment 12. B. Paratype IEOL 6567, seta a with a replacement seta from segment 9. Scale 50 µm.

FIGURE 3. Lacandodrilus paludosus gen. et sp. nov. Internal.Anterior region, dorsal view. A. Holotype IEOL 3190, segments 1–24. B. Paratype IEOL 6565, segments 3–16. dv= dorsal vessel, es= esophagus, gg= genital glands, mf= male funnels, np= nephridia, ov= ovisac, sg= septal glands, sp= spermatheca, sv= seminal vesicles. Scale 1 mm.

FIGURE 4. Lacandodrilus paludosus gen. et sp. nov. Internal. Anterior region, dorsal view. Paratype IEOL 6568, segments 4–10. dv= dorsal vessel, es= esophagus, lc= lateral commisures, sg= septal glands. Scale 0.5 mm.

FIGURE 5. Lacandodrilus paludosus gen. et sp. nov. Internal. A. Holotype IEOL 3190. Dorsal and left side view of segments 9 and 10 (scale 100 µm). B. Paratype IEOL 6568. Dorsal view of segments 15–19 (scale 200 µm). C. Paratype IEOL 6568. Nephiridium in situ of segment 24, right side (scale 100 µm). D. Paratype IEOL 6567. Extracted nephridium of segment 30 (scale 100 µm). dv= dorsal vessel, es= esophagus, gpl= granular peritoneal layer of nephridium, lc= lateral commisures, mf= male funnels, mt= muscular tube of nephridium, nc= nerve cord, nep= nephridia, sc= seminal coagulum, sg= septal glands.

FIGURE 6. Lacandodrilus paludosus gen. et sp. nov. Internal, dorsal view. A. Paratype IEOL 6565, segments 9–13. B. Holotype IEOL 3190, segments 11–14. dv= dorsal vessel, es= esophagus, ff= female funnel, gg= genital glands, mf= male funnels, ovr= ovarium, sg= septal glands, sv= seminal vesicles. Scale 0.5 mm.

FIGURE 7. Lacandodrilus paludosus gen. et sp. nov. A. Paratype IEOL 2312. Internal, dorsal view of segments 11–14, showing the ovaria after removal of esophagus. dv= dorsal vessel, ff= female funnel, nc= nerve cord, nep= nephridia, ovr= ovarium, B. Holotype IEOL 3190, right spermathecae, lateral view. amp= ampulla, du= duct, mf= part of male funnel and seminal coagulum. Scale 100 µm.

FIGURE 8. Geographical location and type of vegetation (patch of palm trees) where Lacandodrilus paludosus gen. et sp. nov. was found.