Halammohydra octopodides Remane, 1927

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 : 463-464

Halammohydra octopodides Remane, 1927

Most of the specimens of Halammohydra octopodides are from Roscoff (32 specimens), particularly from the station “Basse Plate” (21 specimens). Two are from the “Pier at the Youth Hostel” of Helgoland ( Table 3). Molecular analyses separate this species into three clusters, H. octopodides 1, 2, and 3. The two specimens from Helgoland are positioned in the H. octopodides 1 clade. Node support values are high for all three mOTUs ( Fig. 1 ). ABGD and bPTP analyses group H. octopodides 1 and 2 together and GMYC separates H. octopodides 1 and 2. All analyses distinguish H. octopodides 1 and 2 from 3, except bPTP of 18S, which groups H. octopodides 2 and 3 together with a low support (SI 2). There are no CO1 sequences available for H. octopodides 2 and 3. K2p values of 16S between H. octopodides 1 and 2 are 0.012 ± 0.005 and thus lower than between H. octopodides 1 and 3 (0.051 ± 0.011) or 2 and 3 (0.049 ± 0.011, SI 3).

Specimens from all three groups have a similar morphology ( Table 4). The ovoid gastric tube is 175 ± 72 µm (n = 24) in length ( Fig. 2c ). In some specimens, the body is slightly elongated. The aboral cone is triangular or round and 54 ± 10 µm (n = 16) in length and 47 ± 6 µm (n = 10) in width. Specimens are very adhesive, which complicated the documentation of the adhesive organ. Whenever it was possible to investigate, the adhesive organ was cup-shaped and sometimes reached deep into the aboral cone.

The total number of tentacles varies from 8 to 14, mostly 10, evenly distributed in both whorls. In contrast to H. vermiformis , there is no clear separation of the direction of both tentacle whorls. Neither of the tentacle whorls has a visible bulb at the base ( Fig. 2c ). Some specimens have a slightly club-shaped base in the subaboral whorl. All tentacles are of slender shape, whereas in the subaboral whorl, they sometimes have an irregular surface. One tentacle (in four specimens two) of the subaboral whorl is about two times longer than the other tentacles ( Fig. 2c ). Most of the specimens have no thickening at the base in this long tentacle, and the structure is the same as in the subaboral whorl. Tentacles in the subaboral whorl are of unequal length. The number of statocysts is 4 or 5.

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