Main Content
< Top page

The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Inanidrilus

Inanidrilus Erseus, 1979 (ref. ID; 5973)

Family Tubificidae: Subfamily Phallodrilinae (ref. ID; 5973)

ref. ID; 5973

Emended definition

Hair setae absent. Ventral setae of XI highly modified into penial setae, one pair at each side; the two setae within the hair morphologically different. Male pores paired in XI. Spermathecal pores paired or unpaired in X. Coelomocytes, if present, small and sparse, not of the "Rhyacodriline type". Alimentary canal absent. Vasa deferentia joining ental, apical ends of spindle-shaped, muscular atria. Penes absent. One compact prostate gland attached by stalk to ectal part of each atrium. Spermathecae paired, or unpaired, slender and with muscular duct. Sperm not as spermatozeugmata in spermathecae. (ref. ID; 5973)

Remarks

It appears likely that Inanidrilus is closely related to another group of gutless Phallodrilinae, viz. the complex including Phallodrilus leukodermatus Giere, 1979, and a number of new species that will be treated by Erseus elsewhere. Inanidrilus and this complex have the same number (two pairs), and pricipally the same arrangement, of penial setae. The penial setae of P. leukodermatus may well represent an ancestral setae and the more highly modified and differentiated setae of Inanidrilus, a derived state. Inanidrilus is kept as a separate genus as it possesses only one prostate per atrium, as opposed to Phallodrilus which has two prostates per atrium. It is possible to assess that the functional importance of the anisomorph setation in Inanidrilus, even without knowing the actual phylgenetic relationships with other phallodrilines. The hooked, shorter setae are almost certainly used as hooks for mutual holding of concopulatants. This interpretation is plausible for most types of penial setae occurring among the Phallodrilinae, including, of course, P. leukodermatus. The longer, more or less blade-shaped setae of the Inanidrilus species are probably used to transfer sperm into the spermathecae of the mate. Similar penial setae are also known from other members of the Phallodrilinae: many species within Adelodrilus Cook, 1969 (Erseus 1978, 1979) and Phallodrilus extremus Erseus, 1979 (Erseus 1979). (ref. ID; 5973)

Type species

Inanidrilus bulbosus Erseus, 1979 (ref. ID; 5973)
  1. Inanidrilus bonomii Erseus, 1984 (ref. ID; 6618)
  2. Inanidrilus bulbosus Erseus, 1979 (ref. ID; 5973)
  3. Inanidrilus falcifer Erseus & Baker, 1982 (ref. ID; 5973 original paper)
  4. Inanidrilus mexicanus Erseus & Baker, 1982 (ref. ID; 5973 original paper)

Inanidrilus bonomii Erseus, 1984 (ref. ID; 6618)

Descriptions

Marine species. (ref. ID; 6618)

Inanidrilus falcifer Erseus & Baker, 1982 (ref. ID; 5973 original paper)

Descriptions

Length more than 1.8 mm, more than 18 segments (no complete specimens available). Diameter at XI in whole-mounted, slightly compressed specimens: 0.10-0.13 mm. Prostomium rounded triangular, slightly longer than wide. Mouth absent. Secondary annulations 6 per segment immediately posterior clitellum. Clitellum extending over 1/2X-XII in holotype, poorly developed in paratypes. Somatic setae bifid, with upper tooth thinner and slightly shorter than lower, and generally with an inconspicuous ligament connecting tip of lower tooth with setal shaft. Bifids 25-35 µm long, 1.0-1.5 µm diameter at node, 2-3 per bundle anteriorly, 2 (exceptionally 1) per bundle in segments posterior to clitellum. Ventral setae of XI modified into penial bundles, each containing two sickle-shaped setae. Smaller seta about 55 µm long, diameter (3.5-4 µm) uniform, ectally bearing a small hook. Other penial seta 85-95 µm long, entally 3-4 µm diameter and round in cross section; however, middle to ectal part of this seta flat and slightly twisted, most ectal part forming extremely thin blade (up to 5 µm wide), which protrudes through male pore. Male pores paired, located in line with ventral setae, posteriorly in XI. Spermathecal pore paired, located in line with ventral setae, anteriorly in X, near intersegmental furrow IX/X. Alimentary canal absent. Chloragogen cells present along nerve cord and main blood vessel. Male genitalia (all structures paired): vas deferens 6-7 µm diameter, about 230-250 µm long, with thick layer of circular muscles along most of its length, only most ental section devoid of (visible) muscles; vas deferens entering apical end of spindle-shaped, slightly curved atrium; atrium 45-55 µm long, 12-13 µm diameter, with thin outer layer of muscles, and inner ciliated epithelium that does not appear to be granulated; atrium opening into small copulatory sac, which also contains ends of penial setae; a large prostate gland attached by short stalk to posterior wall of atrium, slightly ectal to middle of atrium. Spermathecae paired, each consisting of long muscular duct, and globular to pear-shaped, thin-walled ampulla. Spermathecal duct 95-105 µm long, 7-16 µm diameter, with roundish ectal swelling, 18-24 µm diameter. Spermatheca ampulla 29-32 µm long, 20-25 µm diameter, and containing a ring of sperm. (ref. ID; 5973)

Remarks

The characteristic shape of the penial setae distingushies Inanidrills falcifer sp. nov. from both its congeners, I. mexicanus sp. nov. and I. bulbosus. The atria of I. falcifer are smaller and more inconspicuous than those of the other two species. Inanidrilus falcifer has paired spermathecae, as has I. mexicanus, but the structure of these organs differs considerably between the species; the muscular duct accounts for a greater proportion of the total spermathecal length in L. falcifer than it does in I. mexicanus. (ref. ID; 5973)

Habitat

Silty subtidal sands in coral reefs (6 m). (ref. ID; 5973)

Type locality

SW of Holetown, St. James, Caribbean side Barbados, patch of silty sand with coral rubbles, 6 m (collected by C. Erseus: October 25, 1979). (ref. ID; 5973)

Examined materials

  • Holotype: USNM71521, a whole-mounted specimen. (ref. ID; 5973)
  • Paratypes: USNM71522, two whole-mounted specimens; one from type locality, and one from Bellairs Reef (off Coral Reef Club), St. James, Barbados, patch of silty sand, 6 m (October 25, 1979). (ref. ID; 5973)

    Inanidrilus mexicanus Erseus & Baker, 1982 (ref. ID; 5973 original paper)

    Descriptions

    Length (fixed specimens) 6.8-9.8 mm, 47-52 segments. Diameter at XI in whole-mounted, slightly compressed specimens: 0.13-0.19 mm. Prostomium pointed, slightly longer than wide. Mouth and anus absent. Secondary annulations conspicuous, 7-9 (generally 8) per segment in middle and posterior regions of body. Clitellum very poorly developed, but epidermis forming a glandular(?) pad ventrally and anteriorly in XII (i.e. immediately posterior to male pores). Somatic setae bifid, with teeth blunt, equally long and wide. Bifids about 30 µm long, about 1.5 µm in diameter at node, 2, sometimes 3 per bundle throughout body. Ventral setae of XI modified into penial bundles, each of which contains two sickle-shaped, very conspicuous setae; smaller 105-120 µm long, entally 10-12 µm diameter, ectally much narrower, strongly curved, with small ectal hook. Other penial seta 150-170 µm long, entally extremely wide (up to 20-21 µm), ectally narrower and strongly curved. Ectal end of this seta may appear very slender and pointed, but is actually elongate leaf-shaped, with extremely thin edges, and a thicker central "vein", which is continuous with rest of seta. Both penial setae protrude into a complex, thin-walled copulatory sac, the shape of which difficult to observe and which is probably highly variable. Male pores paired, more or less lateral on paired ventral protuberances in posterior part of XI. Spermathecal pores paired, located in lateral lines, anteriorly in X, near intersegmental furrow IX/X. Alimentary canal absent. Chloragogen cells present all along nerve cord and main blood vessel. Male genitalia (all structures paired): vas deferens 9-10 µm diameter along most to its length, more than 400 µm long; muscular linig present along whole vas deferens, but especially well developed (forming a thick muff of circular muscles) in short region close to sperm funnel; atrium slender, 95-160 µm long, 20-22 µm diameter, with distinct outer layer of (longitudinal) muscles, and ciliated and granulated inner epithelium; atrium opening into thin-walled copulatory sac; prostate gland large, oval, attached by muscular stalk to ectal part of atrium. Spermathecae paired, very slender, each consisting of an outer heavily muscular duct (23-28 µm diameter), a middle bulbous portion (28-35 µm diameter) between duct proper and ampulla, and an inner oblong ampulla (17-24 µm diameter) with granulated inner epithelium. Total length of spermathecae 170-215 µm. In the available material, spermatozoa absent, or very few and scattered in spermathecal ampulla. (ref. ID; 5973)

    Remarks

    This new species has male efferent ducts similar to those of Inanidrilus bulbosus. However, the two species are easily distinguished by means of (i) the morphology of their penial setae (the larger penial seta is hairlike and about 500 µm long in I. bulbosus; cf. Erseus 1979, Fig.1), and (ii) the number and morphology of their spermathecae (I. bulbosus has an unpaired, middorsal spermatheca, with a very long, coiled duct without a middle bulbous portion). (ref. ID; 5973)

    Habitat

    Subtidal, very fine sand (mostly carbonate). (ref. ID; 5973)

    Type locality

    SE of Sanibel Island, San Carlos Bay, W coast of Florida, 26 degrees 16'30"N, 82 degrees 38'00"W, 25.9 m, sediment 23.74% silt-clay, 85.93% carbonate (collected by personnel of Mote Marine Laboratory, November 6, 1980). (ref. ID; 5973)

    Examined materials

  • Holotype: USNM71519, a whole-mounted, fully mature specimen. (ref. ID; 5973)
  • Paratypes: USNM71520, three whole-mounted specimens (two fully, one partially mature) from type locality. (ref. ID; 5973)
  • Other material examined: