Arenopontia breviarticulata Mielke, 1975

Sak, Serdar, Karaytuğ, Süphan & Huys, Rony, 2024, Review of Neoleptastacus Nicholls, 1945 (Harpacticoida, Arenopontiidae), including an updated key to species and proposal of Phreatipontia gen. nov., Zootaxa 5525 (1), pp. 1-66 : 46

Arenopontia breviarticulata Mielke, 1975

Arenopontia (Neoleptastacus) breviarticulata Mielke, 1975 : Bodin (1979)

Pararenopontia breviarticulata ( Mielke, 1975) Bodiou & Colomines (1986)

Arenopontia (Pararenopontia) breviarticulata Mielke, 1975 : Bodin (1997)

Original description. Mielke (1975):110–112; Abb. 74 (♂ only).

Type locality. Germany, Schleswig-Holstein, Isle of Sylt, List ; in front of old “Litoralstation List/Sylt”; medium to coarse sandy beach.

Body length. 710 μm (♂).

Remarks. The description of Arenopontia breviarticulata is based on a single male that displays a 2-segmented P1 exopod (exp-2 and -3 fused) and a reduced P5 bearing only one spiniform and two setiform elements. As pointed out by Sak et al. (2008) it remains unconfirmed whether the inner spine of the male P5 (or spinous process when incorporated in the segment) is genuinely absent or was overlooked.The latter is unlikely given that A. breviarticulata , with a recorded male body size of 710 μm, is by far the largest arenopontiid to be described so far. Sak et al. (2008) offered an alternative explanation by comparing Mielke’s (1975) illustration with the P5 observed in the copepodid IV stage of N. indicus ( Rao 1967: fig. 3-22) which shows a similar underdeveloped condition. This may suggest that A. breviarticulata has a paedomorphic morphology which is further substantiated by its 2-segmented P1 exopod, a segmentation pattern that is displayed in copepodid II–IV of N. indicus before a third segment is added at the next moult ( Rao 1967). Conversely, A. breviarticulata has retained the plesiomorphic armature pattern on P2 endopod and P4 exopod. Mielke’s (1975) illustration of the P3 is problematic since it shows an inner seta on exp-3 and two very long setae on enp-2. Such features have not been observed in any other arenopontiid, raising the suspicion that Mielke (1975) did not observe the real P3 but duplicated P4 instead. The only difference between his illustrations of P3 and P4 is the extreme disparity in length of the outer basal seta.

Mielke (1975) described the anal operculum with two lateral “Zacken” (jags, sharp projections) which can be regarded as the positional homologues of the paired lateral spinous processes on the anal somite in the acanthus - group of Neoleptastacus . The very long outer spines on exp-2 of P2 and P4 (and possibly P3) in A. breviarticulata differentiates it from all members of this species group.

Bodin (1979) listed A. breviarticulata under the subgenus A. ( Neoleptastacus ) while Mielke (1975) considered it a member of the subgenus A. ( Arenopontia ). Bodiou & Colomines (1986) placed the species in their new genus Pararenopontia , the validity of which was dismissed by Martínez Arbizu & Moura (1994) on the grounds that it was an artificial taxon uniting species with reduced leg segmentation. Sak et al. (2008) favoured a relationship with the Mesopontia - Onychopontia - Neoleptastacus lineage based on the armature formula of P1 enp-2, displaying one geniculate seta and one outer distal spine.Although the morphology of the anal somite suggests that A. breviarticulata is probably nested within the acanthus -group of the genus Neoleptastacus , it is here treated as a species incertae sedis in the Arenopontiidae and not in Neoleptastacus as proposed by Sak et al. (2008).