Ceratopera axi, (RIEDL, 1954) DEN HARTOG, 1964

CERATOPERA AXI ( RIEDL, 1954) DEN HARTOG, 1964 View in CoL

( FIG. 4A, C, D)

Proxenetes axi Riedl, 1954: 217–220 View in CoL , figs 26–27; Riedl, 1953: 133, 137.

Ceratopera bifida Ehlers & Ax, 1974: 656–660 View in CoL , figs 8, 9; considered a synonym of C. axi View in CoL by Karling, 1986: 212.

Ceratopera axi ( Riedl, 1954) Den Hartog, 1964: 401 View in CoL , 406–407, fig. 11K; Karling, 1986: 211–212, figs 50–57; Artois et al., 2000: 107; Willems et al., 2004a: 334, table 1; Willems et al., 2005a: 88 View Cited Treatment , 96, table 2; Willems et al., 2005b: 1565–1566 View Cited Treatment ; Van Steenkiste et al., 2008: 28–29 View Cited Treatment , fig. 11D–E.

New locality: 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; 03/03/2016) GoogleMaps .

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., 2004a), New Caledonia ( Willems et al., 2005a). East Indian Ocean: La Réunion ( Artois, Vermin & Schockaert, 2000). South Indian Ocean: Kerguelen ( Willems et al., 2005b). 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 MI4042 – MI4045 ). 18S rRNA (GenBank accession # MF321746 View Materials ), 28S rRNA (GenBank accession # MF321756 View Materials ) .

Remarks: Animals fusi- or filiform, between 0.8 and 1.8 mm long ( Fig. 4A). The stylet proper is 118–129 μ m long (x = 123 μ m; n = 4; non-axial: 89–96 μ m) ( Fig. 4C). 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. 4C). 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. 4D). In some individuals, the appendage bifurcates distally and a weakly sclerotized ring could be observed just proximal from this bifurcation.

Ceratopera axi View in CoL has been found in very disjunct geographic locations around the globe. The general appearance and the length of the stylet and bursal appendage differ somewhat among populations (see Willems et al., 2004a). Measurements on the stylet and bursal appendage from the specimens from British Columbia correspond to those from the population from California. The proximal plate of the accessory mantle piece is only mentioned in the specimens from the Galapagos ( Ehlers & Ax, 1974), but is also clearly present in specimens from California and Oregon (figs 50, 51 in Karling, 1986). In addition, specimens from British Columbia also have large adenal rhabdites in the atrial region as is also reported in specimens from California and the Galapagos ( Ehlers & Ax, 1974; Karling, 1986).

Some rhabdocoels and other microturbellarians with wide geographic distributions are now recognized as complexes of cryptic species (e.g. Curini-Galletti & Puccinelli, 1998; Casu & Curini-Galletti, 2004; Delogu & Curini-Galletti, 2009; Tessens, 2012; Scarpa et al., 2016). Cryptic species within these complexes often correspond with distinct morphotypes. Possibly, C. axi View in CoL also consists of such a complex ( Willems et al., 2005a, b; Van Steenkiste et al., 2008), and the above-mentioned morphological similarities suggest the existence of a Pacific morphotype. A thorough taxonomic revision integrating molecular and morphological data from these disjunct populations is necessary to test this hypothesis.