Cheliplana, de Beauchamp, 1927

Gobert, Stefan, Diez, Yander L., Monnens, Marlies, Reygel, Patrick, Van Steenkiste, Niels W. L., Leander, Brian S. & Artois, Tom, 2021, A revision of the genus Cheliplana de Beauchamp, 1927 (Rhabdocoela: Schizorhynchia), with the description of six new species, Zootaxa 4970 (3), pp. 453-494 : 490-492

Brunet (1968) provided an identification key to the species of Cheliplana . Here, we give an updated identification key that should enable the recognition of different species in the field. Hence, our key relies almost exclusively on characters that can be observed on live specimens using a simple microscope setup and it avoids characters only observable on histologically stained serial sections.

1. Each proboscis hook consisting of a long proximal part and a branched tip........................................ 2

- Each proboscis hook a simple, curved hook................................................................ 4

2. Only one seminal vesicle. Epidermis covered by glands resembling warts................................ C. verrucosa

- Two seminal vesicles. Epidermis not as such................................................................ 3

3. Branched part of the proboscis hooks consisting of a pair of solid thorns................................. C. paradoxa

- Branched part of the proboscis hooks consisting of three slender spines................................. C. tridigitata

4. Copulatory organ with a stylet. A cirrus, armed or unarmed, may be present....................................... 5

- Copulatory organ with an unarmed or armed cirrus, never with a stylet........................................... 8

5. Copulatory organ with a complex, broad stylet combined with a cirrus. Cirrus with a striated appearance: striation running diagonally in the proximal part of the stylet and longitudinally over the medial and distal parts of the cirrus...... C. boadeni

- Copulatory organ not as such............................................................................ 6

6. Stylet a relatively long (~43 μm), simple, slightly curved needle, running centrally through the armed cirrus..... C. stylifera

- Stylet very short (~ 10 µm), wide and tube-like. No armed cirrus present.......................................... 7

7. Two seminal vesicles present, one of which of normal build, the other elongate and surrounded by a thick layer of longitudinal muscle. No sclerotised spermatic ducts present.................................................. C. uruguayensis

- Only one seminal vesicle present. A sclerotised spermatic duct connects ovary and bursa........................ C. targa

8. Cirrus unarmed....................................................................................... 9

- Cirrus armed with (small) spines........................................................................ 14

9. Cirrus very long (> 100 µm)............................................................................ 10

- Cirrus much shorter (<50 µm).......................................................................... 12

10. Cirrus winding, without sclerotised longitudinal folds....................................................... 11

- Cirrus not winding. Long, sclerotised folds are present............................................... C. vaginalis

11. Cirrus with a distal sclerotised cap or papilla....................................................... C. terminalis

- Cirrus without a distal sclerotised cap................................................................ C. asica

12. One of the seminal vesicles atrophied, without any connection to the testis and not containing sperm, the other one functional..................................................................................... C. spuriaseminalis

- Both seminal vesicles identical or not, but always functional and containing sperm................................ 13

13. Cirrus with longitudinal ridges, visible as small stripes. Cirrus slightly curved at the proximal end. Vagina externa elongated and not divided into several compartments........................................................ C. rubescens

- Cirrus lacking longitudinal ridges. Cirrus curved slightly distally. Vagina externa long, with a strongly developed musculature and proximally subdivided into three compartments................................................ C. hypergyna

14. One or more accessory cirri present apart from the cirrus itself................................................ 15

- No accessory cirri present............................................................................. 17

15. One accessory cirrus, entirely armed with small spines. Three sclerotic spermatic ducts present............. C. deverticula

- More than one accessory cirrus......................................................................... 16

16. Two elongate accessory cirri, each armed with small spines on one side only, the other side unarmed............ C. textilis

- Three relatively large accessory cirri present. All accessory cirri armed with fine spines covering the entire inner surface................................................................................................. C. curini

17. Ejaculatory duct (including the cirrus) long to very long, with a smooth, sclerotised wall. Spiny part restricted to the distal end, often only to a small distal portion that is widened.......................................................... 18

- Ejaculatory duct shorter and/or armed with spines over its entire length......................................... 23

18. Only a single seminal vesicle present..................................................................... 19

- Two seminal vesicles present........................................................................... 20

19. Seminal vesicle completely caudal, with copulatory bulb oriented forwards.............................. C. gibarenha

- Combination of traits not as described above......................................................... C. schilkei

20. Ejaculatory duct relatively long, with a simple bend......................................................... 21

- Ejaculatory duct very long, with many bends or coiled....................................................... 22

21. Spiny part of the cirrus with strong spines, restricted to the most distal tip................................. C. hiemalis

- Spiny part of the cirrus longer and in two parts: a longer proximal part covered with small spines and a shorter distal part that is widened and covered by larger spines....................................................... C. subproximalis

22. Occurs around the Galápagos archipelago.......................................................... C. pacifica

- Occurs in the Black Sea area.................................................................... C. euxeinos

23. Ejaculatory duct widened in some places and distally forming a wound cirrus. Proximal part of the cirrus showing small spines; distal part armed with spines that increase in size towards the distal end. Distal point of the cirrus surrounded by a sclerotised cap................................................................................................ 24

- Female system without visible cap-shaped structure. Cirrus not as described above................................ 25

24. Obvious, sperm-containing structure occurring alongside the ovary. Short sclerotised cap surrounding the cirrus.................................................................................................... C. curvocirro

- Without such an obvious, sperm-containing structure. Long, urn-shaped sclerotised cap surrounding the cirrus.............................................................................................. C. curacaoensis n. sp.

25. Cirrus consisting of three distinct regions: a proximal part with very fine spines, a median region consisting of a ring of large hooks set in sclerotised ‘pockets’ and a relatively wide distal part with fine spines of up to 8 µm long.................. 26

- Cirrus not as described above........................................................................... 28

26. Proximal cirrus region very short (~ 20 µm) and shorter than the distal part....................................... 27

- Cirrus with a long proximal part, ~ 55 µm long. A pair of seminal vesicles present............................ C. setosa

27. Only a single seminal vesicle present.............................................................. C. evdonini

- Two seminal vesicles present............................................................ C. hawaiiensis n. sp.

28. Only a single seminal vesicle present..................................................................... 29

- Two seminal vesicles present........................................................................... 31

29. Cirrus very short, ‘cup-shaped’. A thinly sclerotised penis papilla is present............................ C. mauii n. sp.

- Cirrus not as described above........................................................................... 30

30. Cirrus consisting of three regions: a tubular part, armed with fine hooks; a distal part with larger spines; between these a girdle of spines set onto sclerotised plates with a cross-section of ~ 3 µm ....................................... C. marcusi

- Cirrus not with three clearly defined zones, slightly curved. The entire cirrus armed with slender, densely packed spines................................................................................................ C. remanei

31. Cirrus conspicuously wide and short, at most three times as long as it is wide..................................... 32

- Cirrus not conspicuously wide and/or short. Cirrus at least three times as long as wide.............................. 36

32. Cirrus asymmetrically armed, with a crescent-shaped curve distally...................................... C. pusilla

- Cirrus not as described above........................................................................... 33

33. Cirrus pear-shaped, with its widest part proximally.................................................. C. piriformis

- Cirrus not pear-shaped................................................................................ 34

34. Armed part of the cirrus with 5–7-µm-long spines distally. Distally, the cirrus transitions into an unarmed channel of roughly the same length as the cirrus, ending in a small, non-sclerotised penis papilla..................................... 35

- Cirrus not as described above, but rather barrel-shaped, with spines of 1.5–2 µm long. Ejaculatory duct slightly widened, directly proximal to the cirrus. Walls of this expansion possibly to some degree sclerotised................ C. microcirrus

35. Entire copulatory bulb measuring ~ 250 µm, with an internal seminal vesicle, consisting of a single part. Cirrus with spines of uniform length, organised in a large number of longitudinal rows..................................... C. gemmifera

- Entire copulatory bulb ~ 80 µm long. Internal seminal vesicle present and consisting of two separate lobes. Hard ring-like structures are present in the ejaculatory duct. Cirrus spines organised in 7–8 longitudinal rows. Spines 10–14 µm long proximally and 5–7 µm distally.......................................................................... C. mamkaevi

36. Male atrium with a blindly ending diverticulum. Prostatic vesicle emptying virtually directly into the cirrus. Cirrus measuring 45–50 μm, with the distal end surrounded by a sclerotised papilla........................................ C. pileola

- Male atrium without diverticle. Cirrus not as described above................................................. 37

37. Cirrus consisting of a rigid, tubular proximal part and a shorter distal, crescent-shaped region, armed with both fine and larger, lamellar spines....................................................................... C. asinaraensis n. sp.

- Cirrus not as described above........................................................................... 38

38. Cirrus rod-shaped, ~30-µm-long and uniform in width. Proboscis with a sclerotised base proximal to the hook supports................................................................................................. C. firmata

- Cirrus not as described above........................................................................... 39

39. Proximally to the armed cirrus, the ejaculatory duct is sclerotised to form a fine, sclerotised tube. Cirrus 20–25 µm long, with spines measuring 2–3 µm. Distal cirrus end consisting of a sclerotised tube of ~ 12 µm, surrounded by a cap or papilla........................................................................................... C. barringtonensis

- Cirrus and ejaculatory duct not as described above.......................................................... 40

40. Cirrus curved or sinusoidal............................................................................. 41

- Cirrus straight, without curves.......................................................................... 45

41. Vagina not obvious on live specimens. Tail never elongated................................................... 42

- Posterior third of the body sometimes elongated into a long tail. Vagina clearly visible on live specimens. Bursa connected to the ovary via three sclerotised spermatic ducts............................................................. 44

42. Cirrus with a highly distinct curve or loop................................................................. 43

- Cirrus sinusoidal........................................................................... C. vestibularis

43. Cirrus slender and very long, showing a distinct loop. Copulatory bulb showing transverse ridges or stripes................................................................................................... C. longissima n. sp.

- Cirrus with a characteristic U-bend in the distal half. Distalmost part of the cirrus somewhat widened...... C. cubana n. sp.

44. Two functional seminal vesicles................................................................. C. varicauda

- One functional seminal vesicle, sometimes a second, smaller, blindly ending seminal vesicle present.......... C. sarnensis

45. Cirrus ~ 55 µm long and completely armed. Spines’ size decreasing towards the distal end. A pair of incompletely fused testes present alongside the pharynx................................................................. C. orthocirra

- Cirrus 45–75 µm long, not as described above............................................................. 46

46. Cirrus with spines of varying thickness and length: proximal spines very short, medial spines long, distal spines short again. Extreme distal end of the cirrus thinly sclerotised and folded over to form a short penis papilla.............. C. canariensis

- Cirrus not as described above, cirrus spines all equal in size................................................... 47

47. Testes clearly paired, on opposite sides of the pharynx and with a connection anterior to the pharynx. Cirrus ~ 45 µm long and asymmetrically armed: spines increasing in length toward the distal end on one side, spines decreasing in length toward the distal end on the other side.................................................................... C. californica

- Only one testis present. Cirrus not as described above........................................................ 48

48. Cirrus ~ 75 µm long. Distal part of the cirrus unarmed and evertable to form a small penis papilla............ C. elkhornica

- Cirrus ~ 25 µm long........................................................................ C. santiaguera