CHAPTER 28 



Joan M. Uebelacker 



FAMILY HESIONIDAE Sars, 1862 



INTRODUCTION 



Hesionids are small (about 2-50 mm), cylindrical to dorsoventrally 

 flattened worms, somewhat similar in size and appearance to the syllids 

 (Chapter 30). With the exception of the large, robust genera such as 

 Hesione and Leocrates , the body is quite fragile, and usually fragments 

 upon collection. The head region is distinctive, usually with two pairs 

 of eyes, two or three antennae, and two palps on the prostomium, plus 2- 

 8 pairs of tentacular cirri on the first 1-4 segments. Nuchal organs 

 are present as a pair of small, ciliated ridges or lobes along the 

 postectal margins of the prostomium. The tentacular segments are aseti- 

 gerous and often small; one or more of the anteriormost segments may not 

 be visible dorsally. Setigers are essentially similar throughout the 

 body, with well-defined subbiramous or biramous parapodia having cirri- 

 form dorsal and ventral cirri. Branchiae are absent. Notosetae, when 

 present, are simple, often specialized, and usually few in number. 

 Neurosetae are composite uni- or bidentate falcigers, usually with a 

 subapical spine or sheath. Blades generally vary in length from quite 

 long in the upper or middle part of the fascicle, to short in the lower 

 part of the fascicle. The pygidium may bear cylindrical anal cirri 

 and/or a flattened anal lamella. The pharynx is muscular and eversible, 

 with a smooth, papillose or fimbriated margin. Jaws are usually absent, 

 but may occur as one or two small chitinous teeth or ridges. 



Hartmann-Schroder (1971:126) split the family into two subfamilies, 

 the Microphthalminae and the Hesioninae. The Microphthalrainae are most- 

 ly minute, interstitial taxa, characterized by filiform antennae, palps 

 and cirri, and an anal lamella in addition to the anal cirri. The 

 Hesioninae are generally larger, with cirriform, often articled anten- 

 nae, palps and cirri, and a pygidium with anal cirri but no lamellae. 

 Among the hesionid genera encountered in the Gulf of Mexico BLM-OCS 

 collections, only Microphthalmus belongs to the Microphthalminae; the 

 remaining genera belong to the Hesioninae. 



Fauchald (1977a) placed the family Hesionidae in the order Phyllo- 

 docida and suborder Nereidiformia (superfamily Nereididacea according to 

 Pettibone, 1982:9). The Hesionidae appear most closely related to the 

 families Pilargidae and Syllidae. 



Thirty or 31 genera are currently recognized in the Hesionidae, of 

 which ten, plus one undescribed genus, occur in Gulf of Mexico BLM-OCS 

 collections. The family consists of 130 or more species; 18 are found 

 on the northern Gulf of Mexico outer continental shelf, including five 

 previously described species, two questionable assignments, and 11 spe- 

 cies potentially new to science. 



PRINCIPAL DIAGNOSTIC CHARACTERS 



The number of pairs of tentacular cirri is usually constant within 

 a genus and is therefore considered of primary importance in assignirg 



28-1 



