Arhynchite hayaoi Tanaka & Nishikawa 2013

Hiroshima Prefecture, Seto Inland Sea, Ikarise Islet at the entrance of Lake Hamana, and Misaki (Sagami Bay), Japan, intertidal to subtidal, sandy to muddy bottoms

In life, trunk colored pinkish yellow and proboscis pale yellow (Fig. 1). Coloration fading to pale white or beige after fixation with formalin. In preserved specimens, TL ranging from 25 to 73 mm (n = 28) and PL ranging from 6 to 33 mm (n = 8). Proboscis, often detached from trunk, elongated and slightly expanded at its extremity, with its proximal end forming small lower cup around mouth. Trunk wall thickened and covered with numerous distinct papillae, especially prominent (up to 1 mm) at both extremities. Trunk musculature consisting of outermost circular, middle longitudinal, and innermost oblique layers, all of which continuous throughout. Paired ventral setae of usual form, with strong interbasal muscle (Fig. 2A), but only very rarely single seta without interbasal muscle in 2 of 6 non-type specimens in TUM Echiurida 1-5. Paired gonoducts situated slightly behind ventral setae (Fig. 2A). Gonostomes situated proximally, each with leaf-like gonostomal lip with smooth margin (Fig. 2B); lip plicated marginally, probably due to fixation in many non-type specimens (TUM Echiurida 1-5, 2-11). Long and convoluted alimentary canal, filled with sand grains and elliptical fecal pellets, ca 2 mm in long axis (Fig. 2A, C). Anterior part of alimentary canal, so-called foregut, divided into pharynx, esophagus, gizzard, and crop (Fig. 2A). Intestine following foregut fastened to trunk wall with numerous thread-like mesenteries and divided into pre-siphonal, siphonal, and post-siphonal parts (Fig. 2A, C). Pre- and post-siphonal parts having a ciliated groove; elongated pre-siphonal part about twice as long as TL (Fig. 2A). Rectal caecum absent (Fig. 2C). Vascular system composed of dorsal, neurointestinal, and ventral vessels, without ring vessel (Fig. 2A). Dorsal vessel attached to entire length of crop (Fig. 2A). Ventral vessel running along almost entire length of ventral nerve cord and terminating at posterior end of post-siphonal intestine near anus (Fig. 2A, C). Neurointestinal vessel, although injured in holotype, issuing from ventral vessel slightly behind gonostomal level and terminating at anterior end of intestine without bifurcation (Fig. 2A). In 6 non-type specimens (5 in TUM Echiurida 2-11 and 1 in TUM Echiurida 1-5), ventral vessel issuing additional branch forward at ventral origin of neurointestinal vessel, with the branch terminally forming small loop around interbasal muscle. Further, in another non-type specimen of TUM Echiurida 1-5, origin of neurointestinal vessel shifted far forward, crossing interbasal muscle but without additional branches. Paired simple anal vesicles, ca one-third of TL in holotype, while rarely attaining TL in other specimens, covered wholly with numerous microscopic ciliated funnels and fastened basally to trunk wall by some mesenteries (Fig. 2C).

Hiroshima Pref. (Seto Inland Sea), Ikarise Islet at the entrance of Lake Hamana, and Misaki (Sagami Bay), Japan, intertidal to subtidal, sandy to muddy bottoms.