Ancorabolina, GEORGE, 2006

Lee, Jimin & Huys, Rony, 2019, New Ancorabolidae (Copepoda: Harpacticoida) from Korea: two new genera, revisionary notes and updated identification keys, Zoological Journal of the Linnean Society 187, pp. 331-377 : 358-359

ANCORABOLINA GEORGE, 2006 C

George (2006c) established the genus Ancorabolina for Ancorabolina chimaera from the Southern Atlantic deep sea, which displayed a combination of ancorabolinid apomorphies (absence of the antennary exopod, transverse elongation of P1 basis) and laophontodinid plesiomorphic character states (antennule ♀ five-segmented; P2–P4 exp-3 with three outer spines). A number of additional apomorphic character states shared between Ancorabolina chimaera and subsets of ancorabolinid taxa were also identified, such as: (1) cephalothorax and/or body somites with dorsal cuticular processes (as in all other Ancorabolinae ); (2) cephalothorax with paired lateral processes near the distal margin (as in Echinopsyllus , Polyascophorus and Pseudechinopsyllus ); (3) pedigerous somites bearing P2–P5 with middorsal tube-pore (as in all other Ancorabolinae ); (4) rostrum small and constricted (as in Dorsiceratus , Polyascophorus , Arthuricornua and Touphapleura ) and with frontal part forming a ‘peak’ (as in all other Ancorabolinae ); (5) segment 1 of antennule elongate and with long spinules along anterior margin (as in the Ceratonotus group); (6) anal somite shorter than wide, trapezoid in shape (as in the Ceratonotus group); and (7) caudal rami elongate and divergent, originating from the outer distal corners of the anal somite and directed upwards (as in the Ceratonotus group). George (2006c) placed Ancorabolina in the Ancorabolinae , solely because it shared only symplesiomorphies with the Laophontodinae , but he did not discuss its relationships with other genera in the subfamily.

In an attempt to refute Huys’ (1990) claim that there is no close relationship between Laophontoidea and Ancorabolidae, George (2006c) proposed a hypothetical scenario of leg 1 evolution in these taxa, in which the condition displayed by Ancorabolina was construed as a missing link in the ancorabolinid lineage.The weakness in this hypothesis lies in the fact that it hinges heavily on the supposed monophyly of the Ancorabolidae , for which there is no tangible evidence. It also requires the removal of genera such as Tapholaophontodes Soyer, 1975 and Algensiella Cottarelli & Baldari, 1987 to a basal position in the ancorabolid tree, pre-dating the split of the two subfamilies.

Gheerardyn & George (2010) added four new species to the genus and re-evaluated its phylogenetic position, narrowing down the number of ancorabolinid autapomorphies from ten (cf. George, 2006c) to only two, i.e. the loss of the antennary exopod, and the frontal part of cephalothorax forming a ‘peak’ (sensu George, 2006b). They also recognized three, previously overlooked, synapomorphies of the Laophontodinae that are shared by Ancorabolina , but are absent in the remaining Ancorabolinae : (1) segment 2 of antennule with outer bump bearing long spinules in both sexes; (2) P1 coxa elongate, produced along the dorsoventral (proximodistal) axis; and (3) outer seta of P1 exp-2 geniculate (note that this element becomes the proximalmost along the outer margin of exp- 2 in species that have a two-segmented exopod ( Tapholaophontodes remotus Cottarelli & Baldari, 1987 and some species of Ancorabolina and Paralaophontodes Lang, 1965 ; see Table 4). In spite of this evidence in support of laophontodinid affinity, Gheerardyn & George (2010) decided to maintain Ancorabolina in Ancorabolinae . Gheerardyn & Lee (2012) reiterated the phylogenetic significance of two of those characters (geniculation of the outer seta on exp-2 of P1 and the presence of an outer bump with long spinules on the second antennulary segment) and proposed them as potential synapomorphies of the Laophontodinae (+ Ancorabolina ). Despite the fact that some of the proposed apomorphies (transverse elongation of P1 basis, elongation of segment 1 of antennule) display a gradual development in Ancorabolina, George & Müller (2013) continued to maintain the genus in an otherwise monophyletic Ancorabolinae .

Previous attempts to shoehorn Ancorabolina into the Ancorabolinae were partly based on an incorrect assessment of the morphology of leg 1. In Ancorabolina chimaera , the basis has not only elongated along the proximodistal axis distad from the coxa-basis joint, but its distal half has also expanded transversely, forming cylindrical pedestals for the exopod and, in particular, the endopod. The presence of a basal pedestal for the endopod is a diagnostic (and potentially apomorphic) character for all members of the Laophontodinae and may be seen as new evidence lending further credence to the position of Ancorabolina in the Laophontodinae . Conversely, in members of the Ancorabolinae , transverse elongation of the basis is not restricted to its distal half, but starts immediately posterior to the coxa-basis joint and involves allometric growth of the entire protopodal segment, even in the most primitive genus Arthropsyllus (cf. Conroy-Dalton & Huys, 2000: figs 13D, 16B, F). Moreover, although most species in this subfamily display a prehensile endopod, none of them possesses a pedestal supporting it. The modifications of leg 1 in Ancorabolina and the remaining Ancorabolinae cannot therefore be considered as homologous and, consequently, the former genus is here reassigned to the Laophontodinae (despite its unfortunate name). Four apomorphic character states lend support to a potential sister-group relationship between Laophontodes gracilipes Lang, 1936b and Ancorabolina (see below - Taxonomic notes on Laophontodes T. Scott, 1894 ).