Euchonicola, Boxshall & O’Reilly & Sikorski & Summerfield, 2019

Boxshall, Geoff A., O’Reilly, Myles, Sikorski, Andrey & Summerfield, Rebecca, 2019, Mesoparasitic copepods (Copepoda: Cyclopoida) associated with polychaete worms in European seas, Zootaxa 4579 (1), pp. 1-69 : 52

Genus Euchonicola gen. nov.

Diagnosis. Adult female body highly transformed, comprising large ectosoma connected via short stalk to small flattened, discoid endosoma located within host. Ectosoma indistinctly segmented, comprising fused cephalothorax and trunk plus small abdomen. Abdomen distinct, unsegmented, bearing median anal slit terminally and paired caudal rami. Cement glands paired, conspicuous in posterior part of trunk of mature females. Egg sacs uniseriate. Endosoma flattened, irregularly discoid, typically elliptical and narrower than width of trunk. Ectosoma with 2 pairs of appendages close to base of stalk. Antennules reduced to unarmed lobes. Antennae 2-segmented, subchelate, comprising robust basal segment and curved apical claw. Other mouthparts and swimming legs all lacking. Male unknown.

Type species: Euchonicola caudatus gen. et sp. nov., by original designation.

Etymology. The name of the new genus is based on a combination of Euchone , the name of the host genus of the type species, and –icola meaning inhabitant: gender masculine.

Remarks. The organization of the body of the new genus is similar to that of saccopsids, with the entire body (cephalothorax, trunk, and small abdomen) forming an indistinctly segmented and undifferentiated ectosoma attached via a short stalk originating ventrally in the oral area which connects to a small flattened endosoma that lies within the host. The oral origin of the stalk is indicated by the positioning of the vestigial antennules and subchelate antennae around the base of the stalk. In some specimens the body appears to exhibit traces of serial subdivision along the longitudinal axis of the trunk region, however, the grooves between these apparent segments coincide with, and probably express, the spacing of the large eggs contained within the oviduct.

The new genus differs from Melinnacheres , Trichobranchicola gen. nov., and Lanassicola gen. nov. in the structure of the antennae and the lack of maxillae in the adult female. In all three of these saccopsine genera the antennae carry paired adhesion pads distally, whereas in Euchonicola gen. nov. the antennae are subchelate, terminating in a curved claw. The saccopsine genera are also characterized by the possession of well developed maxillae bearing paired adhesion pads distally, whereas in Euchonicola gen. nov. the maxillae are lacking.