Trichodrilus, Claparede, 1862

Fend, Steven & Rodriguez, Pilar, 2024, Two new species of Trichodrilus (Annelida, Clitellata, Lumbriculidae) from Pacific drainages, western USA, Zootaxa 5551 (1), pp. 141-156 : 151

Undetermined Trichodrilus species from North America

( Figure 5 )

We have seen poorly preserved individuals of what appear to be additional undescribed Trichodrilus species from other regions in North America. None of these can be clearly attributed to a described species, but as many details are not visible in the few available specimens, they are not erected as new species here.

Material examined: New Mexico, Sandoval Co., East Fork Jemez River at New Mexico Highway 4, approximately N35.83, W106.64, 14 Jun 1998, 2 slide-mounted specimens: 1 mature, dissected; 1 partially-mature, sagittally sectioned .

North Carolina, Hertford Co., Chinkapin Creek at SR1432, N36.2531, W76.8494, 15 Feb 2011, 1 whole mount. 1 Mar 2011, 1 whole mount. Nash Co. , Tar River at NC 581, N35.880, W78.090, 9 Oct 2014, 1 whole mount. 22 Sep 2014, 2 whole mounts.

Descriptive notes: The species from the Jemez River, New Mexico has spermathecae paired in XI only, posterior vasa deferentia forming a loop in XI, and narrow, club-shaped atria with small, inconspicuous penes ( Fig. 5A ). Atrial length is more than 2 times the width, the ampullar muscle layer is very thin, up to 2 μm ( Table 2 ), and vasa deferentia join the ampulla medially. Lateral blood vessels were not seen in posterior segments. The male duct resembles that of Trichodrilus humptulips sp. nov., although that species differs in having two spermathecal segments, XI and XII. Using the key of Rodriguez & Giani (1994), the Jemez River morphotype belongs to Group I, a group of species having spermathecae in XI only, simple-pointed chaetae, and elongate atria. Although Group I species may be weakly separated by characters with high variability, only T. gordeevi Popchenko, 1976 and T. itchaensis Sokolskaya, 1973 have the posterior vasa deferentia entering XI. The atrial muscle layer of the Jemez River species appears much thinner than the 40–50 μm described for T. itchaensis ( Sokolskaya 1973) . The cylindrical atrium with vasa deferentia entering laterally contrasts with the elongate-pyriform atria, with vasa deferentia entering apically, described for T. gordeevi (Fig. 17 in Timm & Popchenko 1978).

Specimens from two sites in North Carolina (southeastern USA) may represent a single additional species, despite apparent differences in atrial morphology. Worms from both sites have paired spermathecae in both XI and XII, posterior vasa deferentia forming a loop in XI, and multiple, unbranched lateral blood vessel pairs in posterior segments ( Fig. 5 D, E ). Although atria in both morphotypes are petiolate, they differ in size and shape: atrial ampullae of two specimens from the Tar River ( Fig. 5B ) are narrowly ovate (about 105 by 65 μm), whereas ampullae of two specimens from Chinkapin Creek ( Fig. 5C ) are nearly spherical (about 160 by 130 μm). One of the Tar River specimens appears to have a short " type 2" penis, formed by the extruded lining of the atrial duct, and also has a ring of small, petiolate glands surrounding the spermathecal pores ( Fig. 5B ). These characters were not seen in the other specimens, possibly due to poor preservation or orientation. Using the key of Rodriguez & Giani (1994), both of these morphotypes belong to Group II on the basis of reproductive structures. Trichodrilus Group II includes several European species that can be difficult to distinguish, due to high character variability, although only four of those species have prominent lateral blood vessels in posterior segments. This character has not previously been observed in North American Trichodrilus species, although at least 12 European species (including T. allobrogum ) have been described with multiple pairs of lateral blood vessels in posterior segments ( Rodriguez & Giani 1994).

Seven Palearctic Trichodrilus species have two spermathecal segments and lateral blood vessels in posterior segments, but most differ from the North Carolina species in key characters. Trichodrilus capilliformis Rodriguez & Giani, 1994 has hair-like dorsal chaetae, T. leruthi Hrabĕ, 1937 has a penial bulb and tubular atria, T. aporophorus Popchenko, 1976 has branched lateral blood vessels, T. cantabrigiensis lacks the post-septal loop of the posterior vas deferens, T. macroporophorus Hrabě, 1954 has distinct, large male porophores and thick (20 µm) atrial musculature, and T. intermedius has long tubular atria with the wide vasa deferentia entering apically (see Table 1 ). Trichodrilus allobrogum appears to be the most similar species in general morphology of the male duct, although it was described as having a thicker (5–10 μm) atrial muscle layer ( Table 2 ) and the short penis and accessory glands at the spermathecal pores (seen in one of the North Carolina specimens) have not been described in T. allobrogum . Trichodrilus allobrogum is a relatively widespread European species, occurring in surface waters ( Hrabĕ 1937), and was provisionally recorded as " Trichodrilus allobrogum Claparède (?)" from Illinois by Kindred (1918). That record has been considered doubtful, as Kindred was unable to see several key characters (including blood vessels, atrial morphology, and posterior male funnels and vasa deferentia) in the single specimen. Kindred compared his specimen with the three accepted congeners at the time of that publication: T. allobrogum , T. pragensis and T. sanguineus (Bretscher) (the latter now Stylodrilus , see Achurra et al. 2015). Two other species with the same reproductive pattern, but not mentioned by Kindred, were placed in other genera at the time: T. cantabrigiensis ( Beddard, 1908) (as Phreatothrix ), and T. intermedius ( Fauvel, 1903) (as Trichodriloides ). Although Kindred considered it difficult to positively attribute that specimen, it is far more difficult to compare his description with more recent treatments of the genus [19 species in Cook (1971a), 34 in Rodriguez & Giani (1994)]. As the specimen appeared to be incomplete, its identity could not be confirmed by Cook (1971b). The only other North American record noted by Cook (1971b) was an incompletely mature specimen, which could not be identified to species.

Figures

FIGURE 5. Undetermined Trichodrilus species. A. Specimen from Jemez River, New Mexico, reproductive organs in X– XII. B. Specimen from Tar River, North Carolina, reproductive organs in X–XII. C. Specimen from Chinkapin Creek, North Carolina, atrium. D–E Specimens from North Carolina, lateral blood vessels in posterior segments; (D) dorsal view (Tar River), (E) lateral view (Chinkapin Creek).