Ancorabolina, AND

Gheerardyn, Hendrik & George, Kai Horst, 2010, New representatives of the genus Ancorabolina George, 2006 (Copepoda, Harpacticoida, Ancorabolidae) including remarks on ancorabolid phylogeny, Zoological Journal of the Linnean Society 158 (1), pp. 16-55 : 53-54

ANCORABOLINA AND LAOPHONTODES BICORNIS

As mentioned above in the discussion of character 4, the laophontodin species La. bicornis strongly resembles the species of Ancorabolina . The fact that it shares character 16 with Ancorabolina causes some confusion in the phylogenetic interpretation. In fact, the very first examinations of A. chimaera (mis-)lead to the assumption of it being a somewhat derived La. bicornis . However, we conclude that the differences between La. bicornis and Ancorabolina are so great that their union is rendered questionable. Table 2 lists several morphological differences based on the redescription by Sars (1908) and personal observations of La. bicornis from G. O. Sars’ collection and our own. Some of the characteristics ( Table 2: 1, 2, 3, 4) are of particular phylogenetic value because their presence in Ancorabolina characterize it as a member of Ancorabolinae ( George, 2006c; see above), whereas their absence in La. bicornis clearly shows its membership of Laophontodinae . At the moment, we refrain from providing a more extensive phylogenetic discussion. Any discussion restricted to Ancorabolina and the single laophontodin species La. bicornis would be premature as it would ignore the much more complicated conditions within Ancorabolidae and the complex relations between the members of both Ancorabolinae and Laophontodinae . This points again to the urgent need for a phylogenetic re-evaluation of Laophontodinae .

Two other species of Laophontodes , Laophontodes hamatus (Thomson, 1882) and La. ornatus , are also characterized by a pair of ventrolateral cuticular processes on the cephalothorax. The poor quality of the original description of La. hamatus led Gurney (1927) to conclude conspecificity with La. bicornis and the latter to be regarded as a junior synonym. However, this proposition was later rejected by Lang (1934) based on slight morphological differences in the rostrum and the two last body somites. Pending re-examination of the type material of La. hamatus , we refrain from drawing conclusions on the validity of this species. Also, the shortcomings in the original description of La. ornatus by Krishnaswamy (1957) obviously cast doubts on the validity of that taxon and prevents any comparison with Ancorabolina .

P1–5, first to fifth thoracopods.

PHYLOGENY INSIDE ANCORABOLINA

Species within Ancorabolina can be differentiated from each other on account of the proportional lengths of rostrum, first antennular segment and furcal rami, the degree of development of the posterior processes on the cephalothorax, the number of exopodal segments in P1, and the degree of transverse elongation of the P1 basis. There is a clear trend towards progressive elongation in the rostrum (which is also progressively curved ventrally), first antennular segment, and furcal rami, and transverse elongation of the P1 basis. These characters are shown as morphoclines, which are difficult to dissolve into discrete character states. As the species show a mix of less or more derived conditions of the different characters, assessing relationships within the genus is particularly difficult. Contrary to the striking morphological variation of the above characters, the chaetotaxy of P2–P5 is the same in all known species of Ancorabolina , except for A. chimaera which lacks the inner seta on enp-2 of P4 and female P3.

At present, the genus Ancorabolina shows a considerably wide distribution range, from the bathyal north-east Atlantic and eastern Mediterranean Sea to the abyssal south-east Atlantic Ocean.