Restudy Of The Gourd-shaped Prianulids From The Cambrian Chengjiang Biota And Their Phvlogeny

Sicyophorus rara Luo&Hu 1999 and Palaeopriapulitesparvus Hou et al.,1999,are two gourd-shaped priapulids from the Cheng iang Biota in the Cambrian Series 2 Stage 3.There is a three-dimensional gut different from the other fossil priapulids,in introvert similar to the extant priapulids9 and a lorica of the trunk similar to the larvae of the extant pripulids and loriciferans.However the morphological characteristics and systematic classification of these gourd-shaped priapulids have always been controversial.This thesis focuses on the morphological description of Sicyophorus rara and Palaeopriapulites parvus.Findings show:S.rara 6-10 mm in length,The body divided into five sections from anterior to posterior,which include:the pharynx,the collar,the introvert,the neck and the trunk.Pharynx with teeth could be retracted and everted into introvert,and has a muscular pharyngeal bulb.Collar is a trapezoidal in structure with papillae below the everted pharynx.Ovoid introvert partly invaginable,with 10 transverse circles and 25-30 longitudinal rows of scalids arranged in the anterior half of the introvert,the posterior introvert is smooth.The neck is a narrow part between introvert and trunk,surface coverd with spines and annulations.Trunk ovoid and larger than wide,with 15-30 longitudinal lorica plates.Gut has a variable shape in different position,straight along in the introvert and heavily coiled or S-shape curve or bead-like in the trunk.P.parvus aslo include five sections,the body length almostly 8-13 mm,with lorica in the margin or no signs in the trunk,the gut straight from the pharynx to the end of the trunk.Due to the diversity of gut morphology the author believes that the curvature of the gut should not be used as the identification character of species.Based on the study of the type specimen(fossil number:NIGP115446),it is considered that P.parvus is most probably a synonym of 5.rara.Based on ontogeny and phylogeny of gourd-shaped priapulids,P.parvus and S.rara are two different development stages of S.rara.