A new family of harpacticoid copepods and an analysis of the phylogenetic relationships within the Laophontoidea T. Scott

Abstract

A new family Cristacoxidae is proposed to accommodate the monotypic genera Cristacoxa gen. nov., Noodtorthopsyllus Lang (ex Canthocamptidae) and Cubanocleta Petkovski (ex Laophontidae). Cristacoxa petkovskii gen. et spec. nov. is described on the basis of a single male collected from coralline sand of Bonaire, West Indies. N. psammophilus Noodt and C. noodti Petkovski are redescribed and refigured on the basis of new material from the Galápagos (Isla Santa Cruz), the West Indian Islands (Curaçao, Klein Curaçao, Bonaire) and the Canary Islands (El Hierro, Tenerife). The new family is characterised by the presence of an outer spinous process on the first antennular segment, the absence of the antennary exopod, the uniramous mandibular palp, the presence of conspicuous cristae on the precoxa and coxa of leg 1 and the elongation of the apical exopodal spines of P2 to P4. The Cristacoxidae are unique in having an equal number of setae/spines onthe P5 in both sexes. Examination of the ontogeny of this leg in males and females of Orthopsyllus spec. gives strong evidence that the cristacoxid P5 has undergone neotenous evolution. Males of Cristacoxidae are readily recognisable by their extremely long spermatophores. The new family is allocated to the superfamily Laophontoidea T. Scott, together with the Laophontidae T. Scott, the Laophontopsidae Huys & Willems, the Orthopsyllidae Huys and the Adenopleurellidae Huys. A phylogenetic analysis of the relationships within the superfamily is presented, and as a result Por’s (1986) concept of the Laophontoidea is refuted. Instead, it is concluded that the superfamily can be defined on the basis of the following apomorphies: (1) antennules with outer spinous process on segment 2; (2) antenna with allobasis bearing 1 seta; (3) antennary exopod quadrisetose; (4) P1 exopod without inner seta on exp-2 and 4 setae/spines on exp-3; (5) P1 endopod 2-segmented with elongated enp-1 and 2 elements on enp-2; (6) P2—P4 with 2-segmented endopods; exp-1 without inner seta; (7) sexual dimorphism of P3 endopod; (8) P6 bisetose with one member fused to somite. There is no close relationship neither with the Normanellidae Lang, nor with the Ancorabolidae T. Scott. The Laophontidae are considered the first offshoot in the evolution of the Laophontoidea because of the retention of the 8-segmented antennule in both sexes and the ancestral seta formulae on P2–P4. The other families can be assigned to two clades: the Adenopleurellidaeand the Laophontopsidae-Cristacoxidae- Orthopsyllidae-grouping. The Laophontopsidae and the Cristacoxidae are sister groups because of the shared sexual dimorphism of the P3 endopod (advanced type), and the fusion of antennular segments distal to the geniculation in the male. Emphasis is placed on the postembryonic development in the Laophontoidea of the male P3 endopod and P6 and on their homologies in the female. A reconstruction of the hypothetical ancestor of the Laophontoideais presented.