TREATISE ONLINE Number 109 Part V, Second Revision, Chapter 2: Class Enteropneusta: Introduction, Morphology, Life Habits, Systematic Descriptions, and Future Research Christopher B. Cameron 2018 Lawrence, Kansas, USA ISSN 2153-4012 paleo.ku.edu/treatiseonline Enteropneusta 1 PART V, SECOND REVISION, CHAPTER 2: CLASS ENTEROPNEUSTA: INTRODUCTION, MORPHOLOGY, LIFE HABITS, SYSTEMATIC DESCRIPTIONS, AND FUTURE RESEARCH CHRISTOPHER B. CAMERON [Département de sciences biologiques, Université de Montréal, Montréal QC, H2V 2S9, Canada,
[email protected]] Class ENTEROPNEUSTA MORPHOLOGY Gegenbaur, 1870 The acorn worm body is arranged [nom. correct. HAECKEL, 1879, p. 469 pro Enteropneusti GEGENBAUR, into an anterior proboscis, a collar, and a 1870, p. 158] posterior trunk (Fig. 1). Body length can Free living, solitary, worms ranging from vary from less than a millimeter (WORSAAE lengths of less than a millimeter to 1.5 & others, 2012) to 1.5 meters (SPENGEL, meters; entirely marine; body tripartite, 1893). The proboscis is muscular and its with proboscis, collar, and trunk; proboscis epidermis replete with sensory, ciliated, coelom contains heart-kidney-stomochord and glandular cells (BENITO & PARDOS, complex; preoral ciliary organ posterior- 1997). Acorn worms deposit-feed by trap- ventral; collagenous Y-shaped nuchal skel- ping sediment in mucus and transporting eton extends from proboscis through neck it to the mouth with cilia. A pre-oral ciliary before bifurcating into paired horns in organ on the posterior proboscis (BRAMBEL & collar; paired dorsal perihaemal coeloms COLE, 1939) (Fig. 2.1) directs the food-laden associated with collar dorsal blood vessel; mucous thread into the mouth (GONZALEZ anterior trunk pharynx perforated with & CAMERON, 2009). The proboscis coelom paired gill slits that connect via atria to contains a turgid stomochord (Fig.