Figure 1. Cavitary marine nematodes. A in Paraphyly of Marimermithida refines primary routes of transition to parasitism in roundworms

Figure 1. Cavitary marine nematodes. A, Marimermis maritima: 1, live specimens exposed in open host, sea urchin Strongylocentrotus polyacanthus; 2, 3, cephalic end apically and laterally, respectively, scanning electron microphotograph; pharyngeal gland outlets on lips, abundant irregular somatic setae; 4, generalized anterior ends juxtaposed in M. maritima [modified from Tchesunov (1997a)] and Thoracostomopsis barbata (Enoplida: Thoracostomopsidae) [modified from Lorenzen (1994)]. B, Aborjinia sp.: 1, juvenile occupying introvert of Priapulus caudatus (photograph courtesy of Dr A. S. Maiorova, NSCMB FEB RAS); 2, generalized anterior ends juxtaposed in Aborjinia sp. and Leptosomatum sp. (Enoplida: Leptosomatidae); 3, anterior body with two-celled ventral secretory-excretory gland, a distinctive genus feature [redrawn and modified from Miljutin (2003)]. C, Nematimermis enopliƲora: 1, two mature parasitoid individuals within host body of nematode Enoplus communis (Enoplida: Enoplidae); 2, 3, anterior body and head of immature parasitoid retrieved from body cavity of E. communis; 4, 5, anterior and tail regions of mature parasitoid from E. communis; trophosome resorbed, embryos with larval stylet inside egg cases, nested retained exuvia (old moulted cuticles) [all drawings modified from Tchesunov & Spiridonov (1993)]. (See also Fig. S1.) Key: a, amphid; emb ova, embryonated eggs; ep g, epidermal glands; ils, inner labial sensilla; ols + cs, joint crown of outer labial and cephalic setae; paras ind, parasitoid individuals; ph g, pharyngeal glands; ph t, pharyngeal tube; ss, somatic setae; stylet, spear-shaped armature; tr, trophosome; vgc, ventral gland cells.