Pterodrilus leiteri Williams & Phillips, 2021

Williams, Bronwyn W. & Phillips, Anna J., 2021, A new species of Pterodrilus (Branchiobdellida: Clitellata) from the upper Yadkin-Pee Dee River Basin of North Carolina, Journal of Natural History 55 (23 - 24), pp. 1491-1498 : 1493-1496

Pterodrilus leiteri Williams & Phillips , sp. nov.

Figure 1 a-c.

Type Locality

Basin Creek below Longbottom Road (CR 1730), Wilkes County, North Carolina, USA.

Holotype

NCSM 28393 (adult), removed from Cambarus longulus Girard, 1852 ( NCSM 28420 ). Collected 6 November 2017 by B.W. Williams, P.G. Weaver, M.A. Perkins, and S.G. Anderson.

Paratypes

NCSM 28394 , 28403 , 28406 , 28409 , 28413 , 28419 (adults), N = 6 USNM 1658085–1658090 (adults), all recovered from Cambarus longulus ( NCSM 28420 ) . Collected at the type locality 6 November 2017 by B.W. Williams, P.G. Weaver, M.A. Perkins, and S.G. Anderson.

Additional material examined

NCSM 28395–28397, 28399–28402, 28404, 28405, 28408, 28412, 28415, 28417, 28418.

Diagnosis

Length about 0.90 mm, head slightly wider than segment 1, body terete slim, segments distinct, prominent transverse ridges segments 2–8, three pairs of twinned digitiform appendages segments 3–5, four unbranched appendages segment 8, supernumary muscles present; dorsal lip smooth, lateral lips absent, ventral lip median emargination; oral papillae present; jaws small, subrectangular, teeth small, dental formula 5/4; pharyngeal sulcus one pair; glandular atrium ovoid, length 0.5x segmental diameter, deferent lobes absent; prostate arising third from ectal end, length 0.6x glandular atrium, differentiated, ental bulb absent; muscular atrium terete, length 0.2x segment diameter; bursa ovoid, length 0.4x segment diameter, penial sheath ental 0.4, penis pyriform, protrusible; spermatheca length 1.2x segment diameter, duct tubular, length 0.4x organ, bulb tubular, length 0.6x organ, ental process absent.

Description

A single anterior nephridiopore opens dorso-medially on body segment 3, the vasa deferentia enter the glandular atrium entally, and the prostate gland arises from the ectal third of the glandular atrium. These characters, together with a dorsal ridge on segment 8 bearing digitiform projections, place the species in the genus Pterodrilus . Twenty-four adult specimens averaged 0.9 mm in length (SD ± 0.085 mm), ranging from 0.71 to 1.01 mm. The head is slightly wider than segment 1 and distinct from the slender terete body. Segments 2–8 have prominent transverse ridges across the dorsal and lateral surfaces, and all ridges contain supernumary muscles. Segments 3–5 each support one pair of dorsal unbranched, digitiform appendages separated medially. Segment 8 displays a pronounced dorso-lateral ridge with four unbranched digitiform dorsal appendages appearing in a fan-like arrangement ( Figure 1a ).

The peristomium comprises a dorsal lip with a smooth margin, no lateral lobes, and a ventral lip bearing a median emargination. Oral papillae, which surround the mouth, are indistinct. The jaws are small, spanning less than 0.2x the diameter of the head, and approximately equal in size. Both jaws are subrectangular and slightly concave, with sharply pointed teeth arrayed in a dental formula of 5/4 ( Figure 1b ). The pharynx has one pair of sulci, although a second smaller pair of sulci, just posterior to the jaws, may be discerned in a handful of the individuals examined.

The male reproductive organs – as observed in a lateral aspect – span nearly the entire diameter of segment 6 ( Figure 1c ). The glandular atrium displays a slightly flattened ovoid shape, with a length approximately 0.5x the diameter of the segment. The prostate gland is tubular, arising from the ectal third of the glandular atrium, and terminating at, or slightly past, the ental edge of the glandular atrium. The prostate gland contains highly vacuolated, i.e. ‘differentiated’ cells. The line of demarcation between these differentiated cells and those undifferentiated from the cells of the glandular atrium varies in several Pterodrilus species , namely Pterodrilus cedrus , Pterodrilus hobbsi , and Pterodrilus robinae , but was consistent in appearance in all 24 P. leiteri sp. nov. specimens examined. An ental bulb is absent. The muscular atrium is terete, with a length 0.2x segment diameter. The bursa is ovoid and 0.4x the segment diameter in length. The penial sheath is contained within the ental two-fifths of the bursa and surrounds the pyriform protrusible penis.

The spermatheca has a length approximately 1.2x that of the diameter of segment 5 ( Figure 1c ). The duct is 0.4x the total length of the organ. The bulb, 0.6x the total length of the organ, retains its tubular shape regardless of if sperm is present or absent. Given the length of the spermatheca, the ental end of the bulb is nearly always reflexed adjacent to the body wall. An ental process is absent.

Variations

A pair of twinned, unbranched, digitiform dorsal projections are typically displayed on segments 3, 4, and 5, but we observed one individual (NCSM 28409) on which a third short central digitiform projection was present on both segments 3 and 4. The dorsal projections on segments 3, 4, 5, and 8 vary in length, ranging from approximately 0.3 to nearly equal the diameter of the body. Although some degree of variation in this respect is expected, the extreme differences observed are likely due to the effects of fixation combined with varying positions of specimens in the mountant.

The reproductive organs in both segments 5 and 6 can be displaced when the gut is filled, often compressing laterally or pushed into the ventral portion of the body cavity; this is a phenomenon that has been observed among numerous branchiobdellidan species. Occasionally, the glandular atrium and prostate are rotated nearly 90° as result of this displacement, resulting in an ‘end on’ view, from the ental end of the two organs back to the ental end of the muscular atrium. In one specimen of P. leiteri sp. nov. (NCSM 28413), the muscular atrium, glandular atrium, and prostate were ‘backwards’ within segment 6, positioned as if mirrored along a vertical plane. As the organs show no sign of having been twisted, it appears that this may be an anomaly formed during development.

Microhabitat

Worms were observed on the host anterior cephalothorax – between the eyes and along the anterior edge of the carapace – and along the lateral margins of the ventral abdomen. We found small cocoons, likely referable to P. leiteri sp. nov., on the anterior cephalothorax only.

Distribution

Currently known only from the type locality.

Host

Cambarus longulus . N.B. Pterodrilus leiteri sp. nov. was not observed on any of the three additional host species that occurred at the type locality: Cambarus bartonii (Fabricius, 1798) , Cambarus johni Cooper, 2006 , and an undescribed member of the Cambarus species C complex (see Williams et al. 2019).

Other symbionts on the host

Branchiobdellidans: Bdellodrilus illuminatus ( Moore, 1894) , Cambarincola fallax Hoffman, 1963 , Pterodrilus alcicornus , Xironodrilus bashaviae Holt & Weigl, 1979 .

Etymology

The species epithet leiteri was formed to recognise the fictional American CIA operative Felix Leiter, whose unwavering support was always appreciated by his British counterpart, James Bond (and vice versa). The root word – masculine in the genitive singular and 2nd declension case – is Latinised according to Article 31.1.2 of the Code ( Ride et al. 1999).

Justification

Only three species in the genus Pterodrilus bear twinned dorsal unbranched digitiform projections anterior to segment 8: P. leiteri sp. nov., P. distichus , and P. robinae ; however, the former can be easily distinguished from the latter two species by the number and position of these projections. Pterodrilus distichus exhibits pairs of unbranched digitiform projections on segments 2 to 7, P. robinae on segments 4 and 5, and P. leiteri sp. nov. on segments 3 through 5. Pterodrilus leiteri sp. nov. can further be distinguished from P. robinae by dental formula (5/4 versus 3/2) and characteristics of the female reproductive structures in segment 5 and male reproductive structures in segment 6. The relative lengths of the spermathecal bulb and duct are consistently 0.6x and 0.4x, respectively, without an ental process, in P. leiteri sp. nov., whereas the spermathecal bulb and duct are 0.3x and 0.6x, respectively, with an ental process, in P. robinae .

Remarks

Gut contents consist primarily of algal material mixed with a clear, amorphous fluid, as observed both in live and fixed specimens. Diatoms are present in the gut of a few specimens. Stalked ciliates occurred on several worms, most frequently along the posterior region of the head or on the dorsal appendages.

Figures

Figure 1. Pterodrilus leiteri sp. nov. a. drawing of the holotype, scale bar = 0.1 mm; b. ventral view of the jaws, dorsal over ventral, with teeth pointing posteriorly, scale bar = 0.01 mm; c. male reproductive system and spermatheca in segments 6 (left) and 5 (right), respectively, holotype, scale bar = 0.1 mm.