Frontonemertes, Iwata, 2006

Iwata, Fumio, 2006, On four monostiliferous hoplonemerteans, including three new genera and species from Washington state and British Columbia, Journal of Natural History 40 (15 - 16), pp. 873-913 : 874-875

Genus Frontonemertes gen. nov.

Type species

Frontonemertes serpentina gen., sp. nov.

Etymology

The generic name is a composite of the Latin prefix fronto (forehead) name nemertes, and refers to the well-developed apical organ of the specimen. The species name alludes to the snake-like form of the worm.

Diagnosis

Monostiliferous marine hoplonemerteans with non-threadlike appearance; with color pattern; cephalic grooves weakly developed on ventral surface of body; ocelli numerous, forming four groups; rhynchocoel, confined to anterior one-third of body length, with wall of two muscle layers; body wall musculature with very sparse lattice-type diagonal layer, longitudinal muscle layer anteriorly divided in parenchyma, its inner portion surrounding brain lobes and rhynchodeum wall, its outer portion reaching together with circular muscle layer into tip of head; cephalic retractor muscles from outer portion of longitudinal musculature well developed; parenchyma well developed; pre-cerebral septum lacking; proboscis insertion formed by fibres from inner portion of longitudinal musculature and by rhynchodeum wall turning internally; rhynchodeum provided with a longitudinal muscle coat derived from inner portion of longitudinal musculature and a weakly-developed sphincter of circular muscles; proboscis armature consisting of a single central stylet and three accessory stylet pouches; stylet bulb without plate-like connective tissue or thick layer of glandular cells; foregut divisible into oesophagus, stomach, pylorus, intestine and hindgut; oesophagus opening into rhynchodeum near anterior end of head; stomach without a small diverticula or caecal folds; intestinal caecum present, without anterior diverticula but with lateral diverticula; main intestinal canal without deep lateral diverticula; blood vascular system with three longitudinal vessels, with simple vascular loop in head, mid-dorsal vessel with single vascular plug; nervous system with neither neurochord cells nor inner neurilemma; lateral nerve cords with one fibrous core with peripheral nerves well developed and without accessory lateral nerves and myofibrillae; single apical organ, frontal glands and cephalic glands present in anterior cephalic region, sub-muscular glands small and few in number; cerebral sensory organ small and anterior to brain; excretory system present, weakly developed in foregut region; sexes separate.

Type species

Frontonemertes serpentina

Body whitish with two lateral orange bands; ventral surface of head with slender cephalic groove and two cephalic V-shaped grooves; dermis thin; anterior chamber of proboscis with two muscle layers (outer circular and inner longitudinal); proboscis with 12 nerves; brain with fibrous connective tissue and without large ganglion cells; mid-dorsal nerve not extending anteriorly beyond the brain; dorsal ganglia not distinctly separated from the ventral ganglia except posteriorly; dorsal ganglia without bifurcated fibre core; paired foregut and rhynchodeum nerves originating from the ventral brain; cerebral sensory organ with fibrous connective tissue; cerebral organ canal, located at anterior end of the cerebral sensory organ; without U-shaped ciliated sensory portion, opening at ventrolateral side of anterior cephalic groove of head; excretory pores ventral to nerve cords and situated in posterior portion of the nephridial region.