Trichobranchicola, 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 : 42

Genus Trichobranchicola gen. nov.

Diagnosis. Adult female body highly transformed, ectosoma comprising anterior cephalothorax, broad trunk and posterior genitoabdomen, connected to small bulla-like endosoma via narrow stalk. Cephalothorax comprising ventrally-projecting frontal region bearing paired antennules distally and antennae near midline close to narrow stalk, and broader posterior region joining to trunk and bearing paired maxillae at base of frontal process. Trunk dorsoventrally flattened, unsegmented, with 2 pairs of lateral setae located posteriorly. Cement glands paired, extending through posterior third of trunk. Genitoabdomen much shorter than wide; bearing large, paired genital apertures plus, on posterior margin, small median prominence with anal slit. Antennule cylindrical, located at distal corner of projecting frontal process and armed with single apical seta. Antennae located near midline of frontal process between antennules; 2-segmented, proximal segment unarmed, distal segment with paired adhesion pads. Maxillae carried on swellings at base of frontal process, unsegmented but distally subdivided into lobate apical pads. Paired setae present laterally on trunk, possibly representing legs 4 and 5. Egg sacs uniseriate, with up to 6 eggs.

Adult male ovoid, indistinctly divided into anterior cephalothorax and posterior trunk. Cephalothorax bearing paired antennules frontally plus antennae; maxillae located laterally. Oral region indistinct. Trunk lacking defined limbs. Caudal rami apparently absent. Antennules unsegmented, unarmed. Antennae 2-segmented with paired apical pads. Maxillae with robust proximal segment and tapering distal segment.

Type species: Trichobranchicola antennatus gen. et sp. nov., by original designation.

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

Remarks. The new genus can be distinguished from Melinnacheres by its body form and the arrangement of its paired appendages. The new genus has a bipartite cephalothorax with a conspicuous ventrally-projecting frontal region which carries paired cylindrical processes, interpreted here as antennules, as well as the typical saccopsine antennae, with paired distal adhesion pads. This frontal region has a narrow base relative to the rest of the cephalothorax which broadens out as it merges into the trunk, but it remains separated from the trunk by a slight surface ridge. The broader posterior part of the cephalothorax carries paired maxillary swellings dorsolaterally. These carry lobate maxillae which are subdivided distally, forming apical pads that appear to assist with attachment to the host. The figured specimen ( Fig. 16C ) was attached to the host by its stalk which originates in the frontal region, but the trunk had been forcibly rotated, providing a clear view of the frontal region.

The posterior margin of the trunk is marked by conspicuous paired genital swellings carrying the paired genital apertures, plus a median anal prominence. This morphology is similar to that exhibited by some Melinnacheres species. Paired cement glands are present in the posterior third of the trunk, with the wider anterior part of each gland forming a swelling visible on the lateral margin of the trunk, and curving posteriorly back towards genital apertures.

The form of the 2-segmented female antennae with paired distal adhesion pads, is the same as in Melinnacheres and on the basis of this shared derived similarity, we place the new genus in the Saccopsidae , subfamily Saccopsinae. It can be distinguished from Melinnacheres by the form of the bipartite cephalothorax of the adult female with its distinct projecting frontal zone bearing paired lobate, unisetose antennules as well as the paired antennae, and by the dorsolateral location and lobate construction of the maxillae.

Figures

FIGURE 16. Trichobranchicola antennatus gen. et sp. nov. female. A, adult female detached from host, dorsal; B, same, ventral; C, attached female rotated so frontal region and paired maxillae visible; D, frontal region, frontal view in situ; E, frontal region showing paired antennules and antennae, with broken base of stalk arrowed; F, maxilla. Scale bars: A–C, 100 µm, D, 50 µm, E–F, 25 µm.