Sathodrilus tetrodonta (Pierantoni, 1906) Gelder, 2024

Gelder, Stuart R., 2024, A reevaluation and redescription of the branchiobdellidan Sathodrilus tetrodonta (Pierantoni, 1906) new comb. (Annelida: Clitellata), Zootaxa 5403 (1), pp. 130-140 : 134-136

Redescription of Sathodrilus tetrodonta (Pierantoni, 1906) n. comb.

( Figure 2A–F )

Branchiobdella tetrodonta Pierantoni, 1906c: 3 , Tav. 5, Figs. 6–8; Pierantoni 1912: 16, Fig. 9A, B; Ellis 1912: 485; Hall 1914: 190; Goodnight 1939: 12, 1940a: 28, 1940b: 170; Holt 1967: 6; Gelder 1996: 659; Timm 1991: 328.

Sathodrilus attenuatus Holt, 1981: 849 ; Kim et al. 1996: 208; Winnepenninckx et al. 1998: 891; Timm 1999: 75; Gelder & Siddall 2001: 217; Siddall et al. 2001: 348; Martin et al. 2000: 357; Martin 2001: 1090; Gelder et al. 2002: 457; Kawai et al. 2004: 863; Gelder 2005: 156; Ohtaka et al. 2005: 152; Bely 2006: 509; Kaygorodova & Sherbakov 2006: 1391; Ohtaka 2007: 484; Rousset et al. 2008: 449; Ohtaka 2010: 465; Nakata et al. 2010: 167; Gelder et al. 2012: 319; Kobayashi 2012: 93; Williams et al. 2013: 32; Gelder & Williams 2015: 553, 2016: 632; Larson & Williams 2016: 438; Gelder 2016: 244; Vedia et al. 2016: 55; Longshaw 2016: 210; Gelder 2019: 490; Gelder 2020: 151; Williams & Weaver 2021: 65; Kitano et al. 2022: 48; Shida & Kawai 2022: 25; Yamauchi & Kawai 2022: 61; Hoshino et al. 2023: 102.

Type material. Pierantoni (1906c: 3) described “ Branchiobdella tetrodonta ” from specimens removed from Astacus klamathensis Stimpson, 1857 (= Pacifastacus leniusculus ( Dana, 1852)) that had been collected from the “fiume Klamath (California)” [Klamath River, California]. However, he neither designated any type specimens, nor stated which institution received the syntypes. Attempts to find any syntypes in alcohol in the NHMW ( Holt 1967: 7, Gelder unpub. data, Subchev & Gelder 2010) as well as other European Museums ( Subchev 2014) have all been unsuccessful.

Sathodrilus attenuatus , holotype ( USNM 65227 ) and 32 paratypes ( USNM 100445a-i ) taken from Pacifastacus (Pacifastacus) leniusculus klamathensis ( Stimpson, 1857) from Elk Creek, about 12.6 miles south of Cottage Grove, Douglas County, Oregon, 11 July 1960 ( Holt 1981: 849).

Etymology. Branchiobdella tetrodonta Pierantoni, 1906c: 3 . No etymology was given, but the species name is an elision of the Greek ‘ tessares ’, meaning ‘four’, and the Greek genitive masculine noun ‘ odontos ’, meaning ‘tooth’ ( Brown 1956), in reference to the worm’s four-tooth jaw. The Latinized prefix ‘ tetra- ’ joins the root ‘ odontus ’, but in this case the ‘- us ’ ending has been changed to ‘- a ’. As Pierantoni’s intention on its form is not known, it must be treated as a noun in apposition, with the original spelling retained according to Art. 31.2.2 ( ICZN 1999).

Description. Specimens are small to medium sized branchiobdellidans, slim in appearance with the body increasing in diameter from segment 1 to a maximum in segment 7. The head is slender and slightly greater in diameter than segment 1 ( Fig. 2D ). The mean body length of adult type specimens is 2.4 mm (n = 29, range 2.0 to 3.1 mm). Peristomium consists of smooth dorsal and ventral lips and is separated from the head by a sulcus with a second shallow sulcus midway along the head. Small, indistinct oral papillae surround the mouth. The jaws are small, yellow to light brown, very similar in size and shape, and triangular in lateral view but rectangular in a frontal view. The teeth are narrow and conical forming a straight line, with a dental formula of 4/4 ( Fig. 2E ). The outer teeth are slightly longer (about 5.0 μm long) than the inner ones (about 4.6 μm long) resulting in their tips forming a visual concave line. A pharyngeal sulcus is present in the organ’s mid region. The slim body is devoid of dorsal segmental ridges, but shallow sulci indicate segments and annuli. Lateral glands on segments 8 and 9 are present, but extensions are absent. The anterior pair of nephridial tubes meet mid-dorsally in a common bulb. These are difficult to see in preserved specimens but easy in live material as the bulb constantly fills with urine and discharges it to the exterior through a nephridial pore about every 30 seconds. The clitellum over segments 5, 6 and 7 is thin. The male reproductive system consists of two pairs of testes, one in each of segments 5 and 6. A pair of sperm funnels are located in each segment and each funnel is connected to a vas efferens that join together in their respective segments to form a vas deferens ( Fig. 2F ). The vas deferens in segment 5 passes into segment 6 where both vasa deferentia enter the glandular atrium independently. The glandular atrium and associated organs are displaced laterally by the gut and fill about half of the ventral segment’s coelom. The glandular atrium length is 0.5x the segment diameter with the two vasa deferentia entering two prominent deferent bulbs giving the organ a Y-shape appearance. The prostate gland is composed of undifferentiated gland cells with an ental bulb; the gland arises from the dorsal glandular atrium about 0.2x from its ectal end and extends to the confluence of the deferent ducts. The ectal end of the atrium transitions into the muscular atrium, about 0.1x segment diameter long, before passing into the subspherical muscular bursa. The muscular atrium transitions into an eversible penis located in the dorsal third of the bursa. In the retracted position the penis is not easy to see but looks like a compressed spring. Ventral to the penis is the bursal atrium with an internal horizontal sulcus that connects to a vertical folded tube which opens externally through the genital pore. The spermatheca is club-shaped, about 0.9x the segment diameter, with an ovoid glandular spermathecal bulb, 0.6x the organ’s length with the remaining 0.4x being the muscular spermathecal duct.

Variations. When the peristomium is not rounded due to contraction, a median emargination is visible in the ventral lip. The width of the head relative to segment 1 varies from about equal to much less and reflects the specimen’s state of extension or contraction on death. The dental formula is usually 4/4 although 5/4 arrangements have been found ( Holt 1981: 849). The arrangement of teeth in Fig. 2B and ventral jaw in Fig. 2E show the outer teeth are slightly longer than the inner two; however, as the jaw position deviates from a frontal view this arrangement will be more difficult or impossible to see. The male organs have the same shape and relative size to each other and point either anteriorly or posteriorly. They occupy either the left or right side of the segment and range in size from filling half ( Fig. 2F ) to the whole side of segment 6. An ental bulb may be visible in the prostate gland. Holt (1981: 851) notes the absence of an ental bulb, but an examination of the holotype and many other preserved and live specimens (Gelder unpub. obs.) revealed one was present. The length of the prostate gland appears to be shorter in some specimens when compared to that of the glandular atrium, but this is likely an artifact due to compression during slide mounting. The muscular atrium ranges from slim tubular to terete. While the length of the spermatheca is constant, the bulb can appear to be slim and ovoid when empty to subspherical when full of sperm. Its position is usually dorso-lateral to the gut, but it can be displaced ventro-laterally making it difficult to see.

Diagnosis. Length 2.2 to 3.1 mm, head width slightly wider than segment 1, body slim terete, segments indistinct; dorsal lip smooth, ventral lip median emargination; oral papillae present; jaws’ size similar, small, shape rectangular, teeth small narrow conical, dental formula 4/4; pharyngeal sulcus one; glandular atrium tubular, length 0.6x segment diameter, deferent lobes prominent (organ Y-shaped); prostate gland tubular, arises at ectal third of glandular atrium, length 0.4x the latter, undifferentiated cells, ental bulb present; muscular atrium tubular, length 0.2x segment diameter; bursa subspherical, penis eversible, in ectal 0.3 of bursa; spermatheca club-shaped, length 0.9x segment diameter, bulb ovoid length 0.6x organ, duct tubular length 0.4x organ, ental process absent.

Distribution—endemic. Type location is the Klamath River, California ( Pierantoni 1906c: 3), while Holt (1981: 851) reported specimens being examined from locations in Benton, Douglas, Lincoln, Marion, Polk counties, Oregon, and Gray’s Harbor and Wahkiakum counties, Washington State, and Lake Tahoe, California ( Gelder, 2005); however, its range was stated as “Streams of the Cascade and Coastal Ranges in Oregon and Washington to the headwater streams of the Snake River in Wyoming ” ( Holt 1981: 851). Observations on live material were made in Lincoln County, Oregon (Gelder, unpub. data) and eastern Shasta County, California (Maria J. Ellis, unpub. data).

Distribution—exotic. As a result of commercial translocations of P. leniusculus to Japan: Hokkaido Prefecture ( Kawai et al. 2004: 863; Ohtaka et al. 2005: 152; Ohtaka 2007: 484; Ohtaka 2010: 465; Yamauchi & Kawai 2022: 52), Fukushima Prefecture ( Kawai et al. 2004: 863), Gunma Prefecture ( Hoshino et al. 2023), Ishikawa Prefecture ( Ohtaka et al. 2005: 152), and Niigata Prefecture ( Shida & Kawai 2022: 25).

Host. Pacifastacus leniusculus ( Dana, 1852) .

Habitat. Live specimens are pink, often forming aggregates on the ventral cephalothorax and carapace with occasional observations on the ventral abdomen. Hosts with S. tetrodonta were often found with cohabiting Cambarincola okadai ( Yamaguchi, 1934) and Xironogiton victoriensis Gelder & Hall, 1990 (Gelder unpub. obs.), and Cambarincola gracilis Robinson, 1954 , Magmatodrilus obscurus ( Goodnight, 1940a) , and Xironogiton victoriensis Gelder & Hall, 1990 (Maria J. Ellis, unpub. data).

Figures

FIGURE 2. Sathodrilus tetrodonta. A. Whole worm lateral view; B. Frontal view of jaws; C. Genital segments 5–6. D. Whole mount lateral view of a paratype (USNM 100445c), scale bar = 0.2 mm; E. Dorsal oblique view of jaws of a paratype (USNM 100445d), scale bar = 10.0 μm; F. Lateral view of genital organs in segments 5 and 6 in a paratype (USNM 100445c), scale bar = 50.0 μm.A–C, from Pierantoni (1906c: Tav. 5) A = Fig. 6, B = Fig. 8, C = Fig. 7, modified by Gelder; D–G, drawings of or from paratypes by Gelder (unpub. obs.). Abbreviations: at, glandular atrium; b, bursa; dl, deferent lobe; eb, ental bulb; ga, glandular atrium; ma, muscular atrium; p, prostate gland; pm, male pore [= genital pore]; sp, developing spermatozoa; spd, sperm duct; spb, spermathecal bulb; spd, spermathecal duct; spf, sperm funnel; spt, spermatheca; t, testis; vd, vas deferens; ve, vas efferens. Note: In Fig. 2C, testes are shown only in segment 5, one sperm funnel, two vas efferens are shown merging into the vas deferens which enters the glandular atrium. Figure 2F is based on a paratype (USNM 100445c) with the sperm funnels and vas efferens added for completeness from other paratypes where they were visible.