Pelagodileptus (ref. ID; 4613 original paper)

[ref. ID; 4613]
Diagnosis; Tracheliidae with flat, unspiralized oral area containing oblong oral opening and oral funnel composed of an inner and outer basket of nematodesmata. With dikinetidal circumoral ciliary row accompanied by many oblique, short preoral ciliary rows on left and two specialized somatic rows on right. (ref. ID; 4613)
Etymology; Composite of the Greek noun pelagios (living in the open sea = planktonic) and Dileptus, indicating relationship with dileptids. (ref. ID; 4613)
Comparison with related genera; Zacharias (1894) established the present species within Dileptus Dujardin because of the dileptid habitus. Awerinzew (1908) transferred it to Amphileptus Ehrenberg because of the oblong oral basket. However, the redescriptions of the synonym Paradileptus cauducs by Fryd-Versavel e al. (1975; Fig. 32) and Packroff & Wilbert (1991; Fig. 31) confirm Zacharias. We establish a new genus for this species, although its oral infraciliature is as in Paradileptus, because it lacks the spirally wounded oral field, which is so prominent in Paradileptus. (ref. ID; 4613)
Type species; Dileptus trachelioides Zacharias, 1894 (ref. ID; 4613)

Pelagodileptus trachelioides (Zacharias, 1894) (ref. ID; 4613 redescribed paper)
Syn; Dileptus saaleri Schwarz, 1962 (ref. ID; 4613); Dileptus trachelioides Zacharias, 1894 (ref. ID; 4613); Paradileptus canellai Dragesco, 1966 (ref. ID; 4613)
Description; 1) Size in vivo 230-800 x 100-300 um, usually 300-600 um long; proboscis up to trunk length. 2) Body club-shaped, that is, trunk broadly to slenderly fusiform with pointed posterior end and short to long motile proboscis; distorted specimens often broadly ellipsoidal and with shortened proboscis. 3) Macronucleus in longitudinal axis of trunk, moniliform composed of 6-27, usually 10-20 globular nodules. 4) Many contract vacuoles, difficult to recognize due to the strongly vacuolized cytoplasm, in dorsal side of proboscis and periphery of trunk. 5) Cells usually green due to innumerable zoochlorellae 2-4 um across and accumulated in posterior trunk region. Cytoplasm very viscous and strongly vacuolized. Two types of rod-shaped (about 2um and 6 um long) extrusomes, mainly in oral bulge of proboscis. 6) About 120-200 meridional ciliary rows. Several rows of paired, short cilia extend left-laterally from base to top of proboscis. 7) Oral apparatus large because extending from anterior trunk end to top of proboscis, lined by circumoral ciliary row; oral basket large and oblong. Proboscis densely ciliated by short, oblique preoral rows on left and two specialized somatic ciliary rows close to right half of circumoral row. 8) Swims slowly to moderately fast up and down, performing circular and dangling movements with the proboscis. Paradileptus elephantinus and P. flagellatus (Rousselet, 1890) Wenrich, 1929 lack symbiotic green algae, are stouter and smaller (150-350 um vs. 300-600 um), and have a large, spiral oral field with a circular, distinct oral basket. Monilicaryon monilatus (Stokes, 1886) Jankowski, 1967, which has similar size and shape as Pelagodileptus trachelioides, is usually benthic, lacks symbiotic green algae, and has a dumb-bell shaped macronucleus and a circular oral basket. 2, 3, 5 (symbiotic green algae), 7 (oral basket oblong) are key characters for identification. (ref. ID; 4613)
Comments; Sometimes misspelled Amphileptus tracheloides. Paradileptus caducus and P. canellai are junior synonyms of Dilpetus tracheloides because they agree in habitat (pelagial), size, nuclear apparatus, and symbiotic green algae; they are, however, much more slender, indicating that they are ecoforms. The number of macronuclear nodules, used by Dragesco (1966) for species distinction, is highly variable. Dilpetus salleri Schwarz, 1962, another planktonic dileptid, is very likely a further synonym of P. tracheloides. The second proboscis near mid-body indicates that Schwarz observed a divider. He did not mention zoochlorellae, possibly because only preserved specimens were studied. (ref. ID; 4613)