taxonID	type	description	language	source
B57CCF07FFBFFF9727870665526FFD09.taxon	description	(FIG. 1) Etymology: The species epithet refers to the word ‘ tillicum’ which means ‘ people, family, tribe and relatives’ in the Chinook jargon of the Pacific Northwest. Type locality: Clover Point, Victoria, British Columbia, Canada (48 ° 24 ′ 12 ″ N, 123 ° 21 ′ 03 ″ W), algae in rocky lower intertidal (02 / 09 / 2015; 03 / 03 / 2016). Type material: Twelve whole mounts, one of which is designated as the holotype (SMNH Type- 8918); the others are paratypes (BBM MI 4021 – MI 4031). Other material: Observations on about 20 live animals. 18 S rRNA (GenBank accession # MF 321753), 28 S rRNA (GenBank accession # MF 321762). Diagnosis: Species of Trigonostomum with 80 - to 92 - μ m-long stylet. Stylet composed of a stylet proper that makes a 90 ° proximal turn, and a mantle consisting of two heteromorph plates with a terminal hook. Distal end of the stylet proper pointed. Bursal appendage 230 – 300 μ m long, consisting of a coiled tube that distally splits into six finer tubes. Finer tubes swollen to vesicles just before the distal end. Description: Live animals between 1.1 and 1.9 mm long. With lenticular eyes of which the reniform pigment zone is often divided into two parts. General appearance typical of species of Trigonostomum with a ciliated epidermis full of rhabdites, adenal rhabdite tracks in the caudal part on both sides of the body, an apical tuft of sensory bristles, a rostral integumental invagination (‘ proboscis’) and a forwardly inclined pharynx with a long prepharyngeal tube in the first body half. Paired gonads behind the pharynx. Large oval testes and seminal vesicles. The latter join and proximally enter the globular prostate vesicle in the rear end of the body. Two types of prostate secretion, a coarse-grained and a fine-grained one, fill the prostate vesicle. Extracapsular parts of the coarse-grained prostate glands were observed in live animals. The sclerotized parts of the male copulatory organ are nearly identical to the one in T. vanmecheleni. The stylet measures 80 – 92 μ m (x = 84 μ m; n = 11; non-axial: 68 – 78 μ m) and consist of (1) a 74 - to 80 - μ m-long (x = 76 μ m; n = 11) and 4 - to 6 - μ m-wide (x = 5 μ m; n = 11) stylet proper that is proximally curved over 90 ° and distally straight with a pointed tip; and (2) a half-open mantle consisting of two heteromorph plates with hooked tips that surround the straight part of the stylet on each side (Fig. 1 B – D). The proximal part of the stylet proper is funnel-shaped and connects to the plates through a system of ridges that fringe the proximal rim of the funnel. The larger plate is 43 – 51 μ m long (x = 47 μ m; n = 11) and 10 – 12 μ m wide (x = 11 μ m; n = 11), while the more slender plate is 38 – 45 μ m long (( x = 42 μ m; n = 11) and 2 – 5 μ m wide (x = 3 μ m; n = 11). The proximal bases of the plates resemble a panhandle. On one side the plate bases connect to the stylet base and on the other side they connect to each other to encompass the stylet proper. The distal part of the plates ends in a hook pointing away from the stylet base. The vitellaria extend dorsally on both sides of the body from behind the pharynx to the ovaries. The large female bursa is elongated and anteriorly provided with a sclerotized bursal appendage. This sclerotized appendage is a coiled, 230 - to 300 - μ m-long tube (x = 261 μ m; n = 10) that is funnel-shaped proximally and distally splits into six slender tubes with a swollen vesicle-like part just before the distal end (Fig. 1 E – G). In some specimens, these six tubes seem to be grouped in two units of three tubes for the first proximal part. Although difficult to observe in the squeezed whole mounts, the appendage seems to make two coils from the proximal funnel to the distal tubes. Discussion: This species clearly belongs to the genus Trigonostomum because of the rostral integumental invagination (‘ proboscis’), the forwardly inclined pharynx, and the construction of the male and female genital system in general and of the stylet and bursal appendage in particular. The stylet is typical for the species group 1 B (stylet with a proximal turn of 90 – 180 °) as defined by Willems et al. (2004 b). Furthermore, based on the morphology of the sclerotized structures, this species is almost identical to T. vanmecheleni from the Italian Adriatic. The latter species belongs to the T. lilliei species group as designated and discussed by Artois et al. (2013) which now comprises four morphologically similar species: T. lilliei (von Graff, 1911 b) Meixner, 1924; T. prytherchi Kepner et al., 1941; T. vanmecheleni and T. tillicum sp. nov. A thorough re-examination of the type material of T. vanmecheleni revealed the stylets to be almost identical to these of the new species from British Columbia. The only notable difference is the size of the stylet, which is about 1 / 3 larger in T. tillicum sp. nov. Artois et al. (2013) describe a spur-like structure on the base of the funnel-like proximal opening of the stylet proper in T. vanmecheleni, which we think corresponds to a protruding ridge on the funnel rim as also observed in T. tillicum sp. nov. The bursal appendages of both species form a coiled tube that splits into six smaller tubes, but is twice as long in T. tillicum sp. nov. as in T. vanmecheleni. In addition, the six smaller tubes consistently display vesicle-like enlargements in T. tillicum sp. nov., which are absent in T. vanmecheleni. Based on the above-mentioned differences and the disjunct geographical distribution, we assign the specimens from British Columbia to a new species. In doing so, we follow Artois et al. (2013) who argue that the morphology of the bursal appendage is a good diagnostic feature within the T. lilliei group. It is nevertheless clear that all species of this group are very closely related, which raises interesting questions on the biogeography of this group given the disjunct localities of these species in the Northwestern Atlantic (T. lilliei, T. prytherchi), Southwestern Atlantic (T. lilliei), Adriatic (T. vanmecheleni), Southwestern Pacific (T. prytherchi) and Northeastern Pacific (T. tillicum sp. nov.). A thorough integrative taxonomic analysis including molecular data from the previously described species will be necessary in the future for a better understanding of species boundaries and diagnostic characters within this group.	en	Van Steenkiste, Niels W. L., Leander, Brian S. (2018): Molecular phylogeny of trigonostomine turbellarians (Platyhelminthes: Rhabdocoela: Trigonostomidae), including four new species from the Northeast Pacific Ocean. Zoological Journal of the Linnean Society 182: 237-257
B57CCF07FFBDFF9627D901BE51F8F9FD.taxon	description	(FIG. 2)	en	Van Steenkiste, Niels W. L., Leander, Brian S. (2018): Molecular phylogeny of trigonostomine turbellarians (Platyhelminthes: Rhabdocoela: Trigonostomidae), including four new species from the Northeast Pacific Ocean. Zoological Journal of the Linnean Society 182: 237-257
B57CCF07FFBDFF9627D901BE51F8F9FD.taxon	description	Known distribution: Northeast Pacific Ocean: California (Karling, 1986). Material: Observations on about 15 live animals. Ten whole mounts (BBM MI 4032 – MI 4041). 18 S rRNA (GenBank accession # MF 321754), 28 S rRNA (GenBank accession # MF 321763). Remarks: Animals about 0.6 – 1.0 mm long. Specimens from Victoria and Calvert Island often with a parenchymatous brownish coloration (Fig. 2 A). General appearance typical of species of Trigonostomum, but larger and plumper than T. tillicum sp. nov. also found at the Victoria locality. Rostral integumental invagination (‘ proboscis’) and forwardly inclined pharynx in the first third of the body. Epidermis packed with oblong to slightly falcate rhabdites and rostral sensory bristles. Internal organization similar to other species of Trigonostomum with paired testes, and paired seminal vesicles entering the prostate vesicle. Bursal canal slightly sclerotized, extremely long and narrow, and partly curled and twisted (Fig. 2 D). Its distal part is somewhat broadened with a constriction right before entering the large oval bursa (arrow in Fig. 2 D). The latter is provided with a sclerotized bursal appendage. Paired ovaries and vitellaria. Stylet and bursal appendage as described by Karling (1986) and Willems et al. (2004 b) (Fig. 2 B – D). The spiral stylets of the specimens from British Columbia and Washington measure 748 – 896 μ m (x = 807 μ m; n = 10) and have five to six coils. In several specimens, the flexible spiral is partly unwound missing one to two full coils. This results in most specimens having five full coils and an unwound part corresponding to roughly one coil. In two specimens from Bamfield only four full coils were counted with one and two unwound sections, respectively. A third specimen from Bamfield has exactly five coils. The bursal appendage measures 75 – 101 μ m (x = 90 μ m; n = 10) (Fig. 2 D). In some specimens, the distal ends of the tubes are slightly funnel-shaped instead of straight. Our measurements for the stylet and bursal appendage are consistent with those for the Californian specimens (683 – 853 and 80 – 106 μ m, respectively; Willems et al., 2004 b). Karling (1986) considered the Californian specimens of T. tori to be representatives of T. setigerum; the latter taxon formerly included all populations with two or more stylet coils. Willems et al. (2004 b) analysed the stylet morphology of all representatives of Trigonostomum from species group 2 (i. e. with a proximal mantle rim closely adhering to the proximal rim of the stylet and enveloping the stylet over its entire length, diverging distally into two spiny plates with a terminal hook) and concluded that the number of stylet coils is constant in different populations. Consequently, Willems et al. (2004 b) split T. setigerum into a number of different species, keeping populations with two coils in T. setigerum and erecting T. australis Willems et al., 2004 b, for the populations with three coils from Queensland and New South Wales, T. galapagoensis (Ehlers & Ax, 1974) Willems et al., 2004 b, for the population with four coils from the Galapagos and T. tori for the population with five coils from California. Willems et al. (2004 b) report that care should be taken when counting the number of coils depending on the angle the stylet is observed from and also mention the occurrence of unwound sections in the longer stylets of the Pacific species. Although it is clear that both these issues are also present in the specimens from British Columbia and Washington, all our specimens have at least five coils when including the unwound portions. In addition to the number of coils, also the size of the stylet and the bursal appendage, and its distribution in the Northeastern Pacific are consistent with the stylet morphology and distribution of T. tori. Therefore, we assign the populations from British Columbia and Washington to this species.	en	Van Steenkiste, Niels W. L., Leander, Brian S. (2018): Molecular phylogeny of trigonostomine turbellarians (Platyhelminthes: Rhabdocoela: Trigonostomidae), including four new species from the Northeast Pacific Ocean. Zoological Journal of the Linnean Society 182: 237-257
B57CCF07FFBCFF96266905A050D4FB71.taxon	diagnosis	New diagnosis: Trigonostominae with afferent system differentiated into a bursa and a sclerotized bursal appendage. Bursa usually with slender bursal canal. Bursal appendage very variable, consisting of a funnel-shaped tube, two slender tubes or a combination of both, with or without a sclerotized ring, sometimes partly protruding into the bursa. Sclerotized parts of the male copulatory organ consisting of a proximally curved stylet proper connected to an accessory mantle at its base. Mantle differentiated into one or several pieces, either plates, tubes, or a combination of both. Accessory mantle either partly sheathing the stylet proper or completely separate from it. Type species: Ceratopera gracilis (von Graff, 1882) Den Hartog, 1964. Remarks: The genus Messoplana is suppressed based on the results of our phylogenetic analysis and the ambiguity of the morphological characters differentiating the representatives of Messoplana and Ceratopera sensu Den Hartog (see discussion C. complicata sp. nov.). All species of Messoplana are transferred to Ceratopera, which now has 26 valid species. A new diagnosis for Ceratopera is provided.	en	Van Steenkiste, Niels W. L., Leander, Brian S. (2018): Molecular phylogeny of trigonostomine turbellarians (Platyhelminthes: Rhabdocoela: Trigonostomidae), including four new species from the Northeast Pacific Ocean. Zoological Journal of the Linnean Society 182: 237-257
B57CCF07FFBCFF9824EF060A517AFDEB.taxon	description	(FIG. 3) Etymology: The species epithet refers to Cascadia, the Pacific Northwest of North America. Type locality: Clover Point, Victoria, British Columbia, Canada (48 ° 24 ′ 12 ″ N, 123 ° 21 ′ 03 ″ W), algae in rocky lower intertidal (16 / 03 / 2015). Type material: One whole mount which is designated as the holotype (SMNH Type- 8919). Other material: Observations on a live animal. Diagnosis: Species of Ceratopera with a 158 - μ m-long stylet. Stylet composed of a stylet proper that makes a 90 ° proximal turn, and a mantle consisting of a proximal girdle bearing two 100 - μ m-long, plate-like tubes with pointed tips. Distal end of the stylet proper pointed. Plate-like tubes provided with a ridge of which at least one has a combed edge. Bursal appendage 91 μ m long, with broad base and spirally curled funnel that distally splits into two short insemination tubes. Description: Animal 1.2 mm long with eyes and some parenchymatous brownish coloration (Fig. 3 A). General appearance much plumper than the more typical fusiform C. axi found at the same locality (Figs 3 A, 4 A). Pharynx slightly anterior to the midpoint of the body. Epidermis packed with oblong rhabdites. Rhabdite tracks present in the anterior body half. Internal organization identical to C. axi with paired testes posterior to the pharynx, paired seminal vesicles entering the prostate vesicle, an elongated bursa with a sclerotized bursal appendage, paired ovaries and vitellaria. The sclerotized parts of the male copulatory organ measure 158 μ m (non-axial: 117 μ m) and consist of (1) a 158 - μ m-long stylet proper that is proximally curved over 90 ° and distally straight with a pointed tip; and (2) a mantle modified into a proximal girdle that modifies into two 100 - μ m-long, plate-like tubes with pointed tips (Fig. 3 B, C). The girdle connects to and surrounds the proximal curved part of the stylet. The distal tubes run adjacent to the stylet and bear a ridge of which at least one has a combed edge (arrow in Fig. 3 B, C). The bursal appendage is typical of Ceratopera and consists of a broad, striated proximal base and a spirally curled, more sclerotized funnel that distally splits into two short insemination tubes (Fig. 3 D, E). The spiral length of the bursal appendage measures 91 μ m. Discussion: This species closely resembles representatives of Ceratopera sensu Den Hartog because of the typical construction of the stylet with a mantle surrounding the stylet proximally and the funnel-shaped bursal appendage. Ceratopera sensu Den Hartog encompassed 11 recognized species, which are discussed in Den Hartog (1964), Ehlers & Ax (1974) and Karling (1986) (but see also the discussion on C. complicata sp. nov. and the general discussion). The mantle associated with the stylet is modified into two structures in only three species of this group: C. sellai (Steinböck, 1933) Den Hartog, 1964, C. levinseni Den Hartog, 1964 and C. reisingeri (Riedl, 1959) Den Hartog, 1964. In the first two species, these modifications consist of elongated plates (‘ lamellae’ in Den Hartog, 1964) proximally originating on a girdle surrounding the stylet, while in the latter species a girdle is absent. The stylet of C. cascadiensis sp. nov. mostly resembles the one of C. sellai as one plate is also tubular and runs closely adjacent to the stylet. However, the other plate in C. sellai is curved and distally modified into a sheet (Den Hartog, 1964), thus differing from the situation in C. cascadiensis sp. nov. Ax (1995) reports on a Greenlandic specimen of Ceratopera he provisionally attributes to C. cfr. levinseni. The elongated stylet of the live specimen he observed (Ax, 1995: figs 14 D, 16) shows a general resemblance to the stylet of C. cascadiensis sp. nov. Although Ax (1995) did not notice any division of the mantle into two ‘ lamellae’, two elongated plates or tubes seem to be present (Ax, 1995: fig. 16 B). Unfortunately, no further details on the morphology of the mantle or the bursal appendage of the Greenlandic specimen are available. As such, this individual remains without a formal species designation.	en	Van Steenkiste, Niels W. L., Leander, Brian S. (2018): Molecular phylogeny of trigonostomine turbellarians (Platyhelminthes: Rhabdocoela: Trigonostomidae), including four new species from the Northeast Pacific Ocean. Zoological Journal of the Linnean Society 182: 237-257
B57CCF07FFB2FF9B27CE0185523AFBB7.taxon	description	(FIG. 4 A, C, D)	en	Van Steenkiste, Niels W. L., Leander, Brian S. (2018): Molecular phylogeny of trigonostomine turbellarians (Platyhelminthes: Rhabdocoela: Trigonostomidae), including four new species from the Northeast Pacific Ocean. Zoological Journal of the Linnean Society 182: 237-257
B57CCF07FFB2FF9B27CE0185523AFBB7.taxon	description	Known distribution: Northeast Pacific Ocean: Oregon and California (Karling, 1986). Central East Pacific Ocean: Galapagos Islands (Ehlers & Ax, 1974). Southwest Pacific Ocean: New South Wales (Willems et al., 2004 a), New Caledonia (Willems et al., 2005 a). East Indian Ocean: La Réunion (Artois, Vermin & Schockaert, 2000). South Indian Ocean: Kerguelen (Willems et al., 2005 b). Southern Ocean: Weddell Sea (Artois et al., 2000). Southwest Atlantic Ocean: Falkland Islands (Karling, 1986), Uruguay (Van Steenkiste et al., 2008). Mediterranean: Gulf of Napels and Sicily (Riedl, 1953, 1954). Material: Observations on seven live animals. Four whole mounts (BBM MI 4042 – MI 4045). 18 S rRNA (GenBank accession # MF 321746), 28 S rRNA (GenBank accession # MF 321756). Remarks: Animals fusi- or filiform, between 0.8 and 1.8 mm long (Fig. 4 A). The stylet proper is 118 – 129 μ m long (x = 123 μ m; n = 4; non-axial: 89 – 96 μ m) (Fig. 4 C). The typical accessory mantle piece of the stylet is S-shaped, with a funnel, and 74 – 81 μ m long (x = 78 μ m; n = 4; non-axial: 70 – 77 μ m). In three out of four whole mounts, the accessory mantle piece connects to the elongated edge of the proximal asymmetrical stylet opening through a proximal plate with a thickened outer edge (arrow in Fig. 4 C). The bursal appendage measures 100 – 118 μ m (x = 108 μ m; n = 4) and has an enlarged mid part in at least two specimens (Fig. 4 D). In some individuals, the appendage bifurcates distally and a weakly sclerotized ring could be observed just proximal from this bifurcation.	en	Van Steenkiste, Niels W. L., Leander, Brian S. (2018): Molecular phylogeny of trigonostomine turbellarians (Platyhelminthes: Rhabdocoela: Trigonostomidae), including four new species from the Northeast Pacific Ocean. Zoological Journal of the Linnean Society 182: 237-257
B57CCF07FFB1FF9B2787077957DAFBF2.taxon	description	(FIG. 4 B, E, F)	en	Van Steenkiste, Niels W. L., Leander, Brian S. (2018): Molecular phylogeny of trigonostomine turbellarians (Platyhelminthes: Rhabdocoela: Trigonostomidae), including four new species from the Northeast Pacific Ocean. Zoological Journal of the Linnean Society 182: 237-257
B57CCF07FFB1FF9B2787077957DAFBF2.taxon	description	Known distribution: Northeast Pacific Ocean: Oregon (Karling, 1986). Material: Observations on five live animals. Three whole mounts (BBM MI 4046 – MI 4048). 18 S rRNA (G e n B a n k a c c e s s i o n # M F 3 2 1 7 4 9), 2 8 S r R N A (GenBank accession # MF 321759). Remarks: Animals are 0.7 – 1 mm long and appear plumper and more Proxenetes- shaped than described by Karling (1986) (Fig. 4 B). Internal organization typical for species of Ceratopera with paired lenticular eyes, rostral rhabdite tracks, a pharynx located mid-body, paired testes situated behind the pharynx, paired ovaries and vitellaria. Two large ovate seminal vesicles are connected to the rounded copulatory bulb. The stylet is 97 – 106 μ m long (x = 100 μ m, n = 3; non-axial: 52 – 57 μ m) and resembles the stylet of C. pilifera as described by Karling (1986). It consists of a curved stylet proper, measuring 74 – 80 μ m (x = 76 μ m, n = 3), with a 23 - to 26 - μ m-long (x = 24 μ m, n = 3) proximal base, and a curved, funnel-shaped, 46 - to 47 - μ m-long (x = 46 μ m, n = 3) accessory mantle piece (Fig. 4 F). These measurements correspond to the ones from the Oregonian specimens. The hair-like eponymous protrusion of the accessory mantle piece could not be observed in our specimens. However, a thickened part of the convex edge of the mantle piece (arrow in Fig. 4 F) corresponds to this structure. Moreover, the needle-like structure on the accessory piece in figure 67 in Karling (1986) could easily be interpreted as a thickened edge rather than a hair-like protrusion. The funnel-shaped and distally curled bursal appendage measures 78 – 88 μ m (x = 82 μ m; n = 3) and is typical for species of Ceratopera sensu Den Hartog. Distally it splits into two 29 - to 32 - μ m-long tubes (x = 31 μ m; n = 3). Based on the strong resemblance of the stylet and bursal appendage with those of C. pilifera, we attribute our specimens to this species.	en	Van Steenkiste, Niels W. L., Leander, Brian S. (2018): Molecular phylogeny of trigonostomine turbellarians (Platyhelminthes: Rhabdocoela: Trigonostomidae), including four new species from the Northeast Pacific Ocean. Zoological Journal of the Linnean Society 182: 237-257
B57CCF07FFB1FF9A2445078557D4F8DE.taxon	description	(FIG. 5 A, C, D)	en	Van Steenkiste, Niels W. L., Leander, Brian S. (2018): Molecular phylogeny of trigonostomine turbellarians (Platyhelminthes: Rhabdocoela: Trigonostomidae), including four new species from the Northeast Pacific Ocean. Zoological Journal of the Linnean Society 182: 237-257
B57CCF07FFB1FF9A2445078557D4F8DE.taxon	description	Known distribution: Northeast Pacific Ocean: California (Karling, 1986). Material: Observations on three live animals. One whole mount (BBM MI 4049). 18 S rRNA (GenBank accession # MF 321748), 28 S rRNA (GenBank accession # MF 321758). Diagnosis: Species of Ceratopera with partly coiled stylet. Stylet composed of a 120 - to 184 - μ m-long, filiform stylet proper with a cup-shaped proximal part, and a 58 - to 64 - μm-long, funnel-shaped accessory mantle piece. Cup of the stylet proper connected to the mantle piece by a sclerotic string; filiform part partially enclosed by the mantle piece. Bursa with bursal canal. Bursal appendage 20 μ m long and consisting of a proximal tube that protrudes into the bursa and distally splits in two smaller tubes. Remarks: Animals about 1.3 mm long, fusiform, with some specimens displaying a parenchymatous brownish coloration (Fig. 5 A). General appearance, internal organization and the morphology of the stylet and bursal appendage correspond with those of ‘ Messoplana pacifica ’ (see Karling, 1986). The stylet proper and the accessory mantle piece of the mounted specimen measure 184 μ m (non-axial: 82 μ m) and 58 μ m (non-axial: 56 μ m), respectively (Fig. 5 D). Although the stylet is a bit larger, this is still in line with the measurements for the Californian specimens (120 – 170 μ m and 58 – 64 μ m, respectively). Bursa, bursal canal and small bursal appendage are faintly visible in the live animal (Fig. 5 C). Karling (1986) attributes his specimens to the genus Messoplana. Although he does not explicitly mention why, he lists some of the features also found in other representatives of this genus such as the mid-body position of the pharynx, a sclerotic string that connects the stylet proper and its accessory piece, a small, bitubular bursal appendage (‘ insemination apparatus’) and a bursa with a bursal canal. Based on the ambiguity of the morphological characters differentiating Messoplana from Ceratopera sensu Den Hartog and the results of our phylogenetic analysis, all species of Messoplana are transferred to Ceratopera. See the discussion on C. complicata sp. nov.	en	Van Steenkiste, Niels W. L., Leander, Brian S. (2018): Molecular phylogeny of trigonostomine turbellarians (Platyhelminthes: Rhabdocoela: Trigonostomidae), including four new species from the Northeast Pacific Ocean. Zoological Journal of the Linnean Society 182: 237-257
B57CCF07FFB7FF9C278F03D6513CFB4F.taxon	description	(FIG. 5 B, E – H) Etymology: The species epithet refers to the complex stylet. Type locality: Clover Point, Victoria, British Columbia, Canada (48 ° 24 ′ 12 ″ N, 123 ° 21 ′ 03 ″ W), algae in rocky lower intertidal (14 / 11 / 2016). Type material: One whole mount which is designated as the holotype (SMNH Type- 8920). Other material: Observations on two live animals. 18 S rRNA (GenBank accession # MF 321747), 28 S rRNA (GenBank accession # MF 321757). Diagnosis: Species of Ceratopera with a very complex stylet. Stylet proper 66 μ m long with a long base and rounded tip. Mantle with numerous plates and a tubular spine. Base of stylet with window-like opening and several ridges. Bursal appendage 48 μ m long, slightly protruding in the bursa, with proximal funnel, slightly sclerotized ring, and two coiled insemination ducts. Description: Animal about 1 mm long, robust with large rostral rhabdite tracks, lenticular eyes and some parenchymatous brownish coloration (Fig. 5 B). Pharynx slightly anterior to the midpoint of the body. Epidermis packed with oblong rhabdites. Internal organization typical for Ceratopera and other Trigonostominae with paired testes posterior to the pharynx, paired seminal vesicles entering the prostate vesicle, an elongated bursa with a sclerotized bursal appendage, paired ovaries and vitellaria. The stylet is 66 μ m long (non-axial: 65 μ m). It is very complex and consists of (1) a curved 66 - μ m-long stylet proper with a rounded tip (x 1) and a very long base (x 2); and (2) a mantle enveloping and connecting to the stylet (Fig. 5 E, F). This mantle is modified into a 52 - μ m-long slender tubular spine with a pointed tip (x 3), a 33 - μ m-long sickle-shaped plate (x 4) running more or less parallel to the stylet proper, and a broad plate with a rounded, slightly combed edge (x 5). Where this combed edge connects to the stylet proper, some smaller overlapping plates (x 6) are present. All these structures come together in the proximal part of the stylet, which has a window-like opening (arrow in Fig. 5 E) and on which several ridges originate. The bursa is long and slender in one animal, likely because of the absence of sperm. In the other animal, the distal part of the bursa is swollen. The latter part is provided with the 48 - μ m-long bursal appendage consisting of a proximal 12 - μ m-long funnel that splits into two spirally curled, 36 - μ m-long insemination tubes (Fig. 5 G). The thick wall of the proximal funnel is confluent with the bursa wall through several sclerotized ridges, but also partly extends into the bursa (arrow in Fig. 5 H). A ring marks the transition between the funnel and the insemination tubes (arrow in Fig. 5 G). This ring seems to be an outward extension of the bursa wall. Discussion: The morphological characters in C. complicata sp. nov. are reminiscent of several taxa within Trigonostominae including Ceratopera sensu Den Hartog, Messoplana, Trigonostomum and Ptychopera. The stylet is very complex as in some species of Trigonostomum and Ptychopera. This is unusual for species of Ceratopera sensu Den Hartog and Messoplana of which most species only have a curved, tubular stylet proper of varying length connected to a tubular spine or plate. These are also the two most prominent features in the stylet of C. complicata sp. nov., but additional plates and ridges result in a very ornate stylet. The bitubular appendage is typical for Messoplana, but the thick-walled, funnel-shaped proximal part is rather wide at its base and connects to the bursa through sclerotized ridges, not unlike species of Ceratopera sensu Den Hartog (e. g. C. pilifera). Den Hartog (1966 a) and Ax (1971) mention a close relationship between Messoplana and Ceratopera sensu Den Hartog (see also general discussion). Both authors clearly define Messoplana by the position of the pharynx in the mid or hind part of the body, the construction of the stylet and its accessory mantle piece, and the morphology of the bursal appendage. However, the position of the pharynx is a dubious feature as species in both genera have representatives with a pharynx in or close to the middle of the body. The morphology of the stylet can be very similar between representatives of Ceratopera sensu Den Hartog and Messoplana. For instance, some species of Ceratopera sensu Den Hartog also have the accessory mantle piece modified into either a separate duct or a tubular spine as in Messoplana; however, according to Den Hartog (1964) the accessory mantle piece in Ceratopera sensu Den Hartog distally connects to and sheaths the straight part of the stylet. This distal connection is not always present in several species of Ceratopera sensu Den Hartog, including C. axi, C. ehlersi, C. pilifera and C. steinboecki (Riedl, 1959) Den Hartog, 1964. Moreover, in several species of Messoplana, such as M. elegans (Luther, 1948) Den Hartog, 1966 a, M. canariensis Ehlers & Ehlers, 1980 and ‘ M. pacifica ’ (now C. pacifica comb. nov.), the stylet proper is also sheathed by the mantle. The bursal appendage is another important diagnostic character used to separate Ceratopera sensu Den Hartog and Messoplana. It consists of a single, funnel-shaped, curved or coiled and strongly sclerotized tube in Ceratopera sensu Den Hartog, while Messoplana typically has two slender ducts surrounded by a sclerotized ring confluent with the bursa wall. The latter type of bursal appendage is shared with Proxenetes; however, Proxenetes differs from Messoplana by its typical stylet surrounded by a closed, funnel-shaped mantle. When looking at the bursal appendage in several species of Ceratopera sensu Den Hartog and Messoplana more closely, the difference in its morphology becomes less apparent. In some species of Ceratopera sensu Den Hartog, including C. cascadiensis sp. nov., C. axi and C. pilifera, the bursal appendage distally bifurcates into two smaller tubes, sometimes with a faintly sclerotized ring around the transition zone (e. g. C. axi). In most species of Messoplana, the proximal part is undivided and partly extends into the bursa. This undivided proximal part can be longer, shorter or the same length as the two tubes. In ‘ M. globulifera Artois et al., 2000 ’, a distal bifurcation is lacking altogether. The examples and discussion above show that the characters separating Messoplana from Ceratopera sensu Den Hartog are equivocal. Not surprisingly, the phylogenetic position of C. pacifica comb. nov. and C. complicata sp. nov. (Fig. 7 A), two species that could either be placed within Ceratopera sensu Den Hartog or Messoplana, reflects the ambiguous taxonomic status of these two genera. It is clear that Ceratopera sensu Den Hartog is not monophyletic when assigning C. complicata sp. nov. to Messoplana and keeping C. pacifica comb. nov. in its original genus. Therefore, the genus Messoplana is suppressed and its representatives are transferred to Ceratopera.	en	Van Steenkiste, Niels W. L., Leander, Brian S. (2018): Molecular phylogeny of trigonostomine turbellarians (Platyhelminthes: Rhabdocoela: Trigonostomidae), including four new species from the Northeast Pacific Ocean. Zoological Journal of the Linnean Society 182: 237-257
B57CCF07FFB6FF9C2669061250A9FF7B.taxon	diagnosis	Diagnosis (amended from Den Hartog, 1964): Trigonostominae with pharynx in the first half of the body. Afferent system differentiated into a large bursa and a small seminal receptacle connected by a narrow spermatic duct. Seminal receptacle connects to the female system through a long, slightly sclerotized duct. Wall of the bursa provided with sclerotized structures (folds or teeth). Sclerotized parts of the male copulatory organ consisting of a stylet proper surrounded by a mantle. Mantle provided with folds, spines or plates. Type species: Ptychopera westbladi (Luther, 1943) Den Hartog, 1964.	en	Van Steenkiste, Niels W. L., Leander, Brian S. (2018): Molecular phylogeny of trigonostomine turbellarians (Platyhelminthes: Rhabdocoela: Trigonostomidae), including four new species from the Northeast Pacific Ocean. Zoological Journal of the Linnean Society 182: 237-257
B57CCF07FFB6FF9C24CF023E57D0FEE1.taxon	description	(FIG. 6 A, F)	en	Van Steenkiste, Niels W. L., Leander, Brian S. (2018): Molecular phylogeny of trigonostomine turbellarians (Platyhelminthes: Rhabdocoela: Trigonostomidae), including four new species from the Northeast Pacific Ocean. Zoological Journal of the Linnean Society 182: 237-257
B57CCF07FFB6FF9F244C026A5721F915.taxon	description	Known distribution: Northwest Pacific Ocean: Japan (Ax, 2008). Material: Observations on eight live animals. Five whole mounts (BBM MI 4050 – MI 4054). 18 S rRNA (G e n B a n k a c c e s s i o n # M F 3 2 1 7 5 1), 2 8 S r R N A (GenBank accession # MF 321760). Remarks: Animals about 0.5 mm long. Live specimens with a parenchymatous brownish to reddish coloration (Fig. 6 A). General appearance typical of species of Ptychopera with the pharynx in the first third of the body right behind the lenticular eyes. Epidermis with oblong rhabdites. Internal organization similar to other species of Ptychopera with paired testes and paired seminal vesicles entering the large, globuliform copulatory bulb. The large bursa appears striated and its basement membrane is slightly sclerotized (Fig. 6 F). It connects to the seminal receptacle through a slender, slightly sclerotized spermatic duct provided with a sphincter. The seminal receptacle in turn connects to the female system through another longer, slightly sclerotized duct (‘ bursal appendage’ in Den Hartog, 1964). Paired ovaries and vitellaria. The stylet measures 67 – 78 μ m (x = 70 μ m; n = 5) and consists of two curved, funnel-shaped and digitiform tubes surrounded by a folded sclerotized mantle that distally ends in a large triangular plate with a serrated edge (Fig. 6 F). The digitiform tubes are of equal length, but differ in width with the wider tube being the stylet proper for the evacuation of sperm and prostate secretion. The more narrow tube connects to the sclerotized mantle at its base. The triangular plate folds over in its proximal half and continues as a weakly sclerotized girdle surrounding and connecting to the stylet in its middle portion. The proximal part of the stylet consists of the bases of the two digitiform plates and has several folds. A slightly curved, slender spur protrudes from the outer edge of one of these folds on the outer side of the larger digitiform tube (arrow in Fig. 6 F).	en	Van Steenkiste, Niels W. L., Leander, Brian S. (2018): Molecular phylogeny of trigonostomine turbellarians (Platyhelminthes: Rhabdocoela: Trigonostomidae), including four new species from the Northeast Pacific Ocean. Zoological Journal of the Linnean Society 182: 237-257
B57CCF07FFB5FF9E24EF05A95609FCDD.taxon	description	(FIG. 6 B, C – E) Etymology: The species epithet refers to the single, horn-like spine in the bursa. Type locality: Clover Point, Victoria, British Columbia, Canada (48 ° 24 ′ 12 ″ N, 123 ° 21 ′ 03 ″ W), algae in rocky lower intertidal (02 / 09 / 2016; 03 / 03 / 2016). Type material: One whole mount which is designated as the holotype (SMNH Type- 8921). Other material: Observations on three live animals. 18 S rRNA (GenBank accession # MF 321752), 28 S rRNA (GenBank accession # MF 321761). Diagnosis: Species of Ptychopera with 46 - μ m-long stylet. Stylet consists of two slightly curved tubes. One tube is longer and club-shaped, the other one is shorter and triangular. Mantle with rounded plate and serrated edge. Bursa with sclerotized folds and an 8 - μ m-long spine. Description: Live animals mostly transparent and measuring about 0.5 – 0.7 mm (Fig. 6 B). General appearance typical of species of Ptychopera with the pharynx in the first half of the body and oblong rhabdites in the epidermis. Internal organization (Fig. 6 E) almost identical to P. japonica and other species of Ptychopera, the only difference being the somewhat more posterior position of the pharynx, the size and construction of the stylet and the presence of a spine in the proximal half of the bursa. The slightly curved stylet consistently measures 46 μ m (x = 46 μ m; n = 4) and is composed of two slightly curved tubes or plates surrounded by a folded sclerotized mantle of which the distal half forms a large rounded plate with a slightly serrated convex edge (Fig. 6 C, D). The two curved tubes differ in length and form. The longer tube on the concave side of the stylet is club-shaped with a rounded distal end while the shorter tube on the convex side of the stylet is more triangular and pointed. The bursa has a slightly sclerotized bursal membrane with sclerotized folds and an 8 - μ m-long spine at its base (Fig. 6 C – E). Discussion: Although the stylet of P. unicornis sp. nov. resembles the stylet of P. japonica, it differs by its smaller size, the more rounded serrated plate, the lack of an extended spur on the mantle, and a marked difference between the form and length of the two slightly curved stylet tubes. P. unicornis sp. nov. also has a spine in the proximal part of the bursa while P. japonica clearly lacks this. Sclerotized folds and ridges in the bursa are common in Ptychopera, but only three other species, P. avicularis Karling, 1974; P. spinifera Den Hartog, 1966 b; and P. purasjokii Ax, 1971, have a single proper spine or teeth at the basis of the bursa. However, these species differ from P. unicornis sp. nov. by their stylet morphology. In addition to differences in stylet morphology, P. unicornis sp. nov. and P. japonica seem to prefer different kinds of intertidal habitats. P. unicornis sp. nov. was found on algae in the marine rocky intertidal, while P. japonica has a preference for slightly brackish intertidal mudflats.	en	Van Steenkiste, Niels W. L., Leander, Brian S. (2018): Molecular phylogeny of trigonostomine turbellarians (Platyhelminthes: Rhabdocoela: Trigonostomidae), including four new species from the Northeast Pacific Ocean. Zoological Journal of the Linnean Society 182: 237-257
B57CCF07FFB5FF9E24EF05A95609FCDD.taxon	diagnosis	Diagnosis (amended from Luther, 1962): Brinkmanniellinae with long, stretchy body. Copulatory organ consists of a proximal copulatory bulb filled with sperm, a middle part containing the ejaculatory duct, and a distal stylet. Stylet is a short tube, with transversal folds and a complex hookshaped distal end. Bursa with proximal, tooth-like folds of the basal membrane. Type species: Tvaerminnea karlingi Luther, 1943.	en	Van Steenkiste, Niels W. L., Leander, Brian S. (2018): Molecular phylogeny of trigonostomine turbellarians (Platyhelminthes: Rhabdocoela: Trigonostomidae), including four new species from the Northeast Pacific Ocean. Zoological Journal of the Linnean Society 182: 237-257
B57CCF07FFB4FF8124E2008A51D0F8EC.taxon	description	(FIG. 6 G)	en	Van Steenkiste, Niels W. L., Leander, Brian S. (2018): Molecular phylogeny of trigonostomine turbellarians (Platyhelminthes: Rhabdocoela: Trigonostomidae), including four new species from the Northeast Pacific Ocean. Zoological Journal of the Linnean Society 182: 237-257
B57CCF07FFB4FF8124E2008A51D0F8EC.taxon	description	Known distribution: Northeast Atlantic Ocean: Baltic Sea (Luther, 1943, 1962; Ax, 1951; Straarup, 1970), Irish Sea (Boaden, 1963), North Sea (Hellwig, 1987). Mediterranean: Gulf of Lion (Ax, 1956). Bosporus (Ax, 1959). Northeast Pacific Ocean: California (Karling, 1986). Material: Observations on two live animals. Three whole mounts (BBM MI 4055 – MI 4057). 18 S rRNA (G e n B a n k a c c e s s i o n # M F 3 2 1 7 5 5), 2 8 S r R N A (GenBank accession # MF 321764). Remarks: Animals as described by Luther (1943, 1962) and Karling (1986). The stylet measures 22 – 27 μ m (x = 25 μ m; n = 3) and consists of a tube, transversal folds and a crescent-shaped plate (Fig. 6 G). The bursa is only visible in the live animals and appears to have one or two tooth-like sclerotized folds. Based on the morphology of this ‘ bursa comb’, Karling (1986) distinguishes two morphotypes: T. karlingi karlingi from the Northeastern Atlantic and Mediterranean, and T. karlingi pacifica from California. Unfortunately, we cannot attribute our specimens to one of these morphotypes, because the bursa comb is not visible in the whole-mounted specimens from British Columbia. Given the disjunct distributions of the Atlantic and Pacific population and the recognition of different morphotypes, it is not unlikely T. karlingi consists of two or more cryptic species (see also discussion on C. axi). MOLECULAR PHYLOGENETIC RELATIONSHIPS The final 18 S and 28 S rRNA sequence data sets comprised 42 taxa and 1723 bp and 36 taxa and 1727 bp, respectively. This results in a concatenated data set (18 S + 28 S) of 42 taxa and 3450 bp for our phylogenetic analyses. Bayesian and ML topologies were congruent. Results of the phylogenetic analyses are summarized in Figure 7 A. The ingroup consists of two clades: (1) a clade with Litucivis serpens Ax & Heller, 1970 (Adenorhynchinae Ax & Heller, 1970), and a polytomy of some representatives of Brinkmanniellinae, including T. karlingi, Cilionema hawaiiensis Karling et al., 1972, and two species of Coronhelmis Luther, 1948; and (2) a clade with several genera of Trigonostominae, including Parapharyngiella Willems et al., 2005 b, Trigonostomum, Beklemischeviella, Proxenetes, Ceratopera and Ptychopera. The outgroup consists of Microvahine corallicola Karling et al., 1972 (Paramesostominae Luther, 1948); Promesostoma marmoratum (Schultze, 1851) von Graff, 1882 (Promesostominae Luther, 1948); Byrsophlebs delamarei (Ax, 1956) Karling, 1985 (Byrsophlebidae von Graff, 1905); and Thalassoplanella collaris Luther, 1946 (Typhloplanidae von Graff, 1905). WithinTrigonostominae, all genera are monophyletic with high support values (bs = 100; pp = 1). Ceratopera sensu Den Hartog is paraphyletic because of the position of C. pacifica comb. nov. (formerly M. pacifica) and C. complicata sp. nov., which are deeply embedded within Ceratopera. Parapharyngiella is the sister taxon of all other genera of Trigonostominae. Phylogenetic relationships among the remainder genera remain partly unresolved except for a sister group relationship between Beklemischeviella and Proxenetes.	en	Van Steenkiste, Niels W. L., Leander, Brian S. (2018): Molecular phylogeny of trigonostomine turbellarians (Platyhelminthes: Rhabdocoela: Trigonostomidae), including four new species from the Northeast Pacific Ocean. Zoological Journal of the Linnean Society 182: 237-257
