Epibionts on Nebalia hessleri
Body length from 815 to 890 µm. No differences in the size between female and male specimens. Body divided into head, neck, trunk and foot. Head with one anterior constriction at the base of the rostrum, and two constrictions close to the neck. Neck has three telescopically retractable pseudosegments, and foot has six telescopically retractable pseudosegments. A non-retractable ring present between second and third pseudosegment of the foot. Trunk has four annulations in its posteriormost part. Trophi has rami, extending caudally into well developed alulae. Epipharynx is asymmetrical, with largest half to the right, consisting of 7 lamellae, and smallest half to the left, consisting of 5 lamellae. Unci is S-shaped, interlocking with rami. Fulcrum lamellar, consisting of 8 to 10 tubular lamellae. Longest lamella present about one-third from dorsal margin of fulcrum.
La Jolla Canyon (32°52.5′N; 117°15.5′W), north of San Diego, California.
Paraseison annulatus
Body is distinctively divided into four regions: head, neck, trunk and foot. The head is elongate and offset from the neck by two conspicuous constrictions. The mouth is terminal, slightly orientated towards ventral side, and surrounded by a well developed rostrum. Rostrum and head are divided by a distinct circular constriction. The corona is completely reduced. Externally the head is characterized by a broad, ventral, longitudinal furrow and additional thinner, longitudinal furrows on the dorsal, lateral and ventral sides. A dorsal antenna is located at about 1/4 from the neck joint; lateral antennae are not present. Internally, the head contains two salivary glands, each with one nucleus, the mastax, a large, caudally extending brain that fills up most of the dorsal part of the head, and paired, elongate retrocerebral sacs. The neck consists of three pseudosegments that can be retracted telescopically. Anteriorly, the first neck pseudosegment joins the rings that mark the intersection with the head. In completely retracted condition no pseudosegmentsare visible. Internally, the neck has a straight oesophagus and an undetermined number of longitudinal retractor muscles. The trunk is fusiform and semiloricate, and divided into a smooth, parallel-sided anterior part with paired longitudinal ventrolateral and dorsolateral sulci, and an annulated posterior part that tapers gradually towards the foot. The anteriormost part is delimitated by a ring, which joins the neck. In the posterior part, at 2/3 from the junction with the neck, four annulations are present and divide the posterior part of the trunk into four non-retractable rings. The posteriormost ring is conspicuously longer than the three anterior ones. Anterior to the annulated trunk part, the outer integument appears wrinkled on the dorsal and ventral side, whereas it is completely smooth laterally. Internally the oesophagus leads to the stomach that fills up most of the trunk. Posteriorly the stomach narrows and leads, in females, to a dorsal cloaca that opens dorsally in the posterior part of the trunk, just at the junction between the foot and the trunk. The male cloaca is located dorsally, in the anteriormost part of the trunk, close to the neck. The foot consists of six telescopically retractable pseudosegments and a distal adhesive disc. An additional ring (apparently not retractable) is present between the second and third foot pseudosegment. Internally the foot is filled with numerous foot glands of varying lengths. A small ovoid gland with a tubular outlet is situated on the ventral side of the foot, close to the adhesive disc.
The trophi are fulcrate and identical in both sexes. The rami are slightly asymmetrical and consist of anteriorly rounded heads that extend caudally into broad alulae. The ramal inner margins are smooth and actual teeth are not present. Only at the anteriormost point of each ramus, a short row with 3 to 4 flattened, knoblike projections is present. The projections appear to interlock with the distal parts of the unci. Posteriorly, the rami extend into a pair of large alulae. Alulae consist of two projections with strongly sclerotized outer margins, dilated distally, and wide inner lamellae. A pore is present anteriorly and laterally close to the transitionof rami into alulae. One additional pair of elements may furthermore be present on the dorsal side of the rami, near the transition into the alulae. Each element resembles a lamellar plate, but since they are partly covered by the epipharynx, it cannot be determined whether they are isolated sclerites, or just thickenings of the rami. A paired lamellar epipharynx is present on the dorsal side of the ramus heads. The right half (7 lamellae) is larger than the left (5 lamellae). The fulcrum is elongated and dilated dorsoventrally in its distal half, smoothly narrowing to an acute point anteriorly. It is made up by 8 to 10 parallel, smoothly tapering lamellae. The shortest lamella is the ventralmost one, whereas the longest is present about one-third from the dorsal side. Unci are elongated and S-shaped, and apically connected with projections of rami.
Dioic species. It reproduces exclusively sexually.
Total length 815–890 µm; head 132–156 µm; neck 187–246 µm; trunk 308–400 µm; foot 142–170 µm; trophi 51 µm; rami 25 µm; fulcrum 39 µm; unci 10 µm.
Paraseison species are probably ectoparasites, and it has been suggested that their unique mastaxes and trophi are used to pierce the tegument of its host by protruding the sharp tip of its fulcrum through the mouth, and sucking out haemolymph of its host.
