Trigonostomum tori, (KARLING, 1986) WILLEMS ET AL., 2004 b

TRIGONOSTOMUM TORI ( KARLING, 1986) WILLEMS ET AL., 2004b

( FIG. 2)

‘ Trigonostomum setigerum Schmidt, 1852 ’ in Karling, 1986: 209–210, figs 45, 46.

Trigonostomum tori ( Karling, 1986) Willems et al., 2004b: 292 , figs 5F, 9F, 10E, table 1.

New localities: Clover Point , Victoria , British Columbia, Canada (48°24 ′ 12 ″ N, 123°21 ′ 03 ″ W), algae in rocky lower intertidal (06/05/2015; 02/09/2015; 14/11/2016). Wizard Island, Bamfield, British Columbia, Canada (48°51 ′ 30 ″ N, 125°09 ′ 33 ″ W), algae in rocky lower intertidal (01/06/2015) GoogleMaps . Dixon Island , Bamfield, British Columbia, Canada (48°51 ′ 05 ″ N, 125°07 ′ 19 ″ W), algae in rocky lower intertidal (02/06/2015) GoogleMaps . Grappler Inlet , Bamfield, British Columbia, Canada (48°50 ′ 17 ″ N, 125°08 ′ 04 ″ W), algae in rocky lower intertidal (30/08/2015) GoogleMaps . West Beach boulders, Calvert Island, British Columbia, Canada (51°39 ′ 07 ″ N, 128°08 ′ 33 ″ W), algae in rocky lower intertidal (09/04/2016) GoogleMaps . Friday Harbor , San Juan Island, Washington, USA (48°32 ′ 42 ″ N, 123°00 ′ 44 ″ W), algae on the dock of the marine station (08/10/2016) GoogleMaps .

Known distribution: Northeast Pacific Ocean: California ( Karling, 1986).

Material: Observations on about 15 live animals. Ten whole mounts (BBM MI4032–MI4041). 18S rRNA (GenBank accession # MF321754 View Materials ), 28S rRNA (GenBank accession # MF321763 View Materials ).

Remarks: Animals about 0.6–1.0 mm long. Specimens from Victoria and Calvert Island often with a parenchymatous brownish coloration ( Fig. 2A). 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. 2D). Its distal part is somewhat broadened with a constriction right before entering the large oval bursa (arrow in Fig. 2D). 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. (2004b) ( Fig. 2B–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. 2D). 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., 2004b).

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. (2004b) 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. (2004b) split T. setigerum into a number of different species, keeping populations with two coils in T. setigerum and erecting T. australis Willems et al., 2004b , for the populations with three coils from Queensland and New South Wales, T. galapagoensis ( Ehlers & Ax, 1974) Willems et al., 2004b , for the population with four coils from the Galapagos and T. tori for the population with five coils from California. Willems et al. (2004b) 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.