Jasmineiricola Boxshall, O'Reilly, Sikorski & Summerfield, 2015, n. gen.

Jasmineiricola n. gen.

Diagnosis. Adult female highly transformed, lacking external segmentation. Body comprising endosoma embedded in host consisting of well defined head region carried anteriorly on trunk bearing paired lateral lobes, and ectosoma consisting of posterior genito-abdominal lobe bearing paired genital apertures. Adult female exhibiting torsion between endosoma and ectosoma. Head bearing rosette-like array of eight slender lobes. Trunk bearing maxillipeds immediately posterior to junction with head. Maxilliped 2-segmented, subchelate. Swimming legs lacking. Genitoabdominal lobe bearing median anus carried on small anal prominence. Caudal rami lacking. Egg sacs paired, arrangement of eggs within sac sometimes linear (uniseriate), typically biseriate or multiseriate. Male unknown.

Type species. Jasmineiricola mackiei n. gen. et n. sp., by original designation.

Etymology. The name of the new genus is derived from the name of the host genus Jasmineira, combined with – icola, meaning inhabitant.

Remarks. The new genus exhibits a unique combination of features that serve to distinguish it from all other copepod genera. None of the families of copepods that have highly transformed unsegmented bodies and live embedded in polychaete hosts, retains a defined cephalothorax bearing lobate vestiges of paired cephalic limbs or has paired maxillipeds on the anterior embedded part of the trunk and a functional anus on the posterior protruding part of the trunk. This unique morphology makes it difficult to place the new genus in any one of the five families of highly transformed copepods living as mesoparasites embedded in polychaetes.

The Herpyllobiidae is one of the better known families (Lützen 1964a, b, 1966, 1968) and currently comprises 27 species placed in five genera (Walter & Boxshall 2015). All adult female herpyllobiids have bodies comprising an embedded endosoma and an external ectosoma and the anus is lacking. No appendages are present in the adult female and all known species are parasites of polynoid polychaetes (Boxshall & Halsey 2004). The new genus differs considerably from herpyllobiids in the positioning of the ovaries within the endosoma rather than the ectosoma, in possessing vestiges of the oral appendages and a pair of subchelate maxillipeds on the endosoma, and in retaining a functional anus on the ectosoma. It is considerably less transformed and lacks key synapomorphies of the Herpyllobiidae, namely loss of all appendages and loss of the anus. In addition, it is found on a sabellid host (order Sabellida) not on a polynoid (order Phyllodocida). The new genus cannot be placed in the Herpyllobiidae.

The Bradophilidae is poorly known although we have been able to examine new bradophilid material from a flabelligerid host (unpublished results). Adult females of Bradophila Levinsen, 1878 are similar to those of the Herpyllobiidae in body form and in lacking all appendages (Marchenkov 2002). These two families differ primarily in characters of the males (Boxshall & Halsey 2004). The male of Jasmineiricola n. gen. is unknown, but the adult female is less transformed and lacks key synapomorphies of the Bradophilidae, such as the loss of all paired limbs. The hosts are also different, with the Bradophilidae exploiting flabelligerid hosts (order Terebellida) while the new genus uses sabellids. The new genus cannot be placed in the Bradophilidae.

The Xenocoelomatidae comprises two genera of highly transformed internal parasites which lack all trace of appendages in mature adults of both sexes. Both genera are cryptogonochoristic, with males reduced to a functional testis housed within a receptaculum masculinum within the female body (Bresciani & Lützen 1974). Species of both genera occur on terebellid hosts. The new genus has a different body organization from xenocoelomatids and utilises hosts from a different order of polychaetes. It does not belong in the Xenocoelomatidae.

Phyllodicolids are currently known only from females and they consist of an unsegmented ectosoma attached to the host by an endosoma consisting of a pair of elongate buccal rootlets (Laubier 1961). Adult females retain up to three pairs of cephalothoracic appendages (identified as antennules, antennae and maxillipeds), according to genus. However, these limbs are carried on the ectosoma, and are positioned around the origins of the buccal rootlets. Phyllodicolids occur on phyllodocid polychaetes (order Phyllodocida) rather than sabellids.The lack of homology of the endosoma and the presence of limbs on the ectosoma, rather than on the endosoma, indicate that the new genus cannot be placed in the Phyllodicolidae.

The Saccopsidae currently comprises four species of the genus Melinnacheres Sars, 1870, all of which occur on terebellid hosts. Adult females of Melinnacheres are similar to phyllodocids in retaining three pairs of appendages on the ectosoma. These limbs have been identified as antennules, antennae and maxillae (Bresciani & Lützen 1975) which, as in phyllodocids, originate around the base of a short stalk that arises in the oral region and penetrates the host. The fundamentally different body organization including the positioning of the ovaries within the endosoma rather than the ectosoma, and the presence of limbs on the ectosoma rather than on the endosoma, indicate that the new genus cannot be placed in the Saccopsidae.

Determining the phylogenetic affinities of secondarily reduced parasitic forms is problematic in the absence of molecular data, but the presence of a large endosoma bearing lobate vestiges of oral appendages and subchelate maxillipeds, plus the retention of a functional anus on the ectosoma is a unique combination of apomorphic and plesiomorphic states and we are unable to place this genus in any existing family. We therefore propose to place it in a new monotypic family, the Jasmineiricolidae, the diagnosis of which corresponds to that of the genus Jasmineiricola n. gen., given above.