Halammohydra vermiformis Swedmark & Teissier, 1957

Tödter, Lenke, Worsaae, Katrine & Schmidt-Rhaesa, Andreas, 2023, Comparative molecular and morphological species delineation of Halammohydra Remane, 1927 (Hydrozoa) - with the description of four new species, Organisms Diversity & Evolution (New York, N. Y.) 23 (3), pp. 455-476 : 459-463

Halammohydra vermiformis Swedmark & Teissier, 1957

A total of 105 specimens are identified as Halammohydra vermiformis by morphological and molecular methods. Fifteen specimens are from Sylt , 76 from Helgoland (45 from “Pier at the Youth Hostel” and 31 from the “Northern intertidal intertidal intertidal

Environment subtidal subtidal and subtidal subtidal and subtidal and subtidal subtidal subtidal subtidal square or opening or square opening

Other tapering mouth tapering mouth Behaviour adhesive adhesive free-swimming adhesive adhesive adhesive adhesive adhesive adhesive

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Length

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± 45 172 - 47 ± 159 ± 348 117 ± 37 227 211 ± 52 301 or 255 - - tube or slightly sometimes Gastric Shape ovoid variable ovoid elongated ovoid, ovoid elongated ovoid ovoid elongated - Statocysts Number 5 8 – 7 5 or 4 6 – – 6 5 4 8 – 7 5 – 9 8, – 7 6 6 – 7

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Length - - 48 8 ± - - - - - -

organ

Adhesive - cup-shaped * * cup-shaped cup-shaped - cup-shaped * - -

conical or cylindrical) Aboral cone Shape - * flat trapezoid conical or - - * conical - - one specimen continued (cluster 4 Table / Species H. teissieri sp n... swedmarki H .. n sp H kerblae . sp n... H joergerae n sp.. / Helgoland “ Sylt ” ” Roscoff “ ” “ Azores 1 ” “ Tenerife “ 2 Tenerife ” - data missing * data from only Beach”), two from Roscoff, and 12 from field trips lacking detailed morphological examination of live animals (eight from Denmark, three from France, Arcachon and one from Cuba; Table 3).

Molecular analyses result in two clusters of this species, H. vermiformis 1 and 2. Both clusters comprise several specimens and support values of 100 in both phylogenetic analyses. Species delimitation tests group them in two clusters with comparably many sequences in each gene ( Figs. 1 , SI 2). 18S sequences do not resolve both groups in ABGD and GMYC, but do resolve them with a low support in bPTP (SI 2). K2p values between both clusters are 0.149 ± 0.019 (16S), 0.003 ± 0.001 (18S), and 0.207 ± 0.020 (CO1) and thus lower than the mean values of all clusters (SI 3). Both clusters differ in the sampling locality. H. vermiformis 1 was sampled exclusively at the subtidal station of Helgoland (“Pier at the Youth Hostel”), H. vermiformis 2 at several intertidal locations, except for the ones from “Ellekildehage” ( Denmark), which was at seven to nine meters depth but in brackish shallow water.

The clear separation into two clusters recognized in molecular analyses is not reflected in the morphology ( Table 4). Both groups have a variety of body shape, ranging from completely round to elongated, with the elongated form dominating ( Fig. 2a ). Halammohydra vermiformis 2 is slightly larger (but with higher variation) with a mean gastric tube length of 298 ± 215 µm (n = 19) compared to 209 ± 75 µm (n = 31) in H. vermiformis 1 in the length of the gastric tube. Most specimens have a conical aboral cone, with a higher length than the width ( Fig. 2b ). The aboral cone of H. vermiformis 2 is slightly larger again (60 ± 12 µm (n = 13) in mean length and 46 ± 8 µm (n = 10) in mean width), compared to H. vermiformis 1 (45 ± 7 µm (n = 21) in mean length and 37 ± 9 µm (n = 28) in mean width). Whenever it was possible to investigate the adhesive organ, it showed a cup- or diamond-/inversed cone shape in the aboral cone ( Fig. 2b ). All specimens have 4 statocysts.

The total number of tentacles is usually 7 (3 aboral + 4 subaboral, Fig. 2a ), with the exception of a few animals from Sylt with 8 (4 + 4) tentacles. No special structure or thickening is documented for the bases of aboral tentacles, and a few specimens have a slight thickening or club-shaped base in the subaboral whorl ( Fig. 2b ). Aboral tentacles are of slender shape. Subaboral tentacles are slightly thicker or with an irregular surface. Within a whorl, the tentacle length is roughly the same, except for the one long tentacle present in the subaboral whorl. It is about two to three times the length of the other tentacles and has a thicker appearance and sometimes a bulb at the base ( Fig. 2a and b ). In some cases, it is coiled up. Aboral tentacles are directed aborally and subaboral tentacles orally ( Fig. 2a ). This was clearly visible while the animals were swimming. In general, specimens observed were less adhesive than other species and mainly found free-swimming with the aboral cone in the direction of movement. Tentacles of the aboral whorl were bent to the oral end while swimming, but the separation of whorls was still visible.

marized species delimitation of ABGD, GMYC, and bPTP results are shown for each cluster

Figures

Fig. 1 Phylogenetic tree of all three genes concatenated with support values of BI/ML (posterior probability/bootstrap value). Nodes with an * have a support of 100/100. Some clusters are collapsed. Sum-

Fig. 2 Light microscopy images of Halammohydra species. a H. vermiformis with a 3 times longer tentacle (arrowhead) in the subaboral whorl. b Magnifi- cation of aboral cone in a show- ing a thickening at the tentacle bases of the subaboral tentacles (arrowhead). c H. octopodides with 2 times longer tentacle (arrowhead). d H. coronata with 1.5 times longer tentacle (arrowhead) in the subaboral whorl. ab, aboral tentacles; ac, aboral cone; ao, adhesive organ; gt, gastric tube; sub, subaboral tentacles