Eumonostilifera

Suborder EUMONOSTILIFERA

Morphological circumscription

Given by Chernyshev (2011a: 191). Monostiliferans having cerebral organs not extending behind the brain (exceptions include Proamphiporus Chernyshev & Polyakova, 2019), with simple canal, but rarely with forked canal bearing a sac-shaped cavity; mouth and rhynchodaeum merge into rhynchostomodeum, or open into a common atrium; rhynchocoel wall of either two-layered (inner longitudinal and outer circular) or interwoven musculature; myofibrils located in fibrous core of lateral nerve cord.

Clade definition

Monostiliferans that are more closely related to Amphiporus lactifloreus (Johnston, 1828) than to Cratenemertes amboinensis (Bürger, 1890).

Remarks

Thollesson & Norenburg (2003: 414) defined Distromatonemertea as “the most inclusive clade comprising all monostiliferous nemertea except Cratenemertea ”. Ambiguity remains in this definition, because Cratenemertea was not clearly defined (see above). In descriptive terms, Distromatonemertea sounds as though it consists only of members with a two-layered rhynchocoel wall, which excludes Plectonemertidae. The name Distromatonemertea in the sense of Thollesson & Norenburg (2003) is thus problematic.

Chernyshev (2003a) placed Enopla (= Hoplonemertea) at the rank of subclass and included in it five orders— Pelagica, Reptantia, Cratenemertea, Eumonostilifera, and Bdellomorpha, abandoning Brinkmann’s (1917) Polystilifera and Monostilifera. Chernyshev (2003 a, 2005a) originally regarded Eumonostilifera as not encompassing Malacobdella. Later, Chernyshev (2011a: 191) amended the diagnosis of Eumonostilifera to accommodate Malacobdella. Although Distromatonemertea has nomenclatural precedence over Eumonostilifera, I here adopt the latter due to the taxonomic uncertainty in the former.