Table 2 Comparison of divergent characters between Rhodope spp. and Helminthope psammobionta

Approx. length/width ratio (contracted - crawling)

8-25

3-9

Habitat

interstitial

littoral, interstitial (some both?)

‘Vesicle’ system

absent

present

Glands of the foot sole

lacking

generally present

Vestigial pharynx

not present

present

Anterior pedal = ‘oral’ glands

paired, tubular

paired, follicular (mixed with ‘true’ oral glands?)

Salivary glands

single, tubular

paired, follicular

Anterior lobe of digestive gland

lacking (or axial connection to esophagus)

extends beyond CNS

Position of intestine/anus

at 4/5 of body length, far from nephropore

at 1/3 of body length, close to nephropore

Form of kidney

sac-like, with proximal filtering duct

two thin branches with interspersed filtering knobs

Form of gonad

tubular, gametogenesis not spatially separated

2-3 posterior testicles, several anterior ovarial follicles

Number of ‘terminal’ glands in gonoduct

1

2

Eyes

with spherical lens, separate from cpg

with corpuscular lens, sitting

Rhinophoral nerve (double roots)

without basal ganglion, with large accessory ganglia

with basal ganglion, accessory ganglia small (or lacking?)

Labiotentacular nerve

undivided, with large accessory ganglia

bifurcated, accessory ganglia small or lacking

Postcerebral accessory ganglia

on ‘pleural’ nerves, also pedal nerves and possibly optic

none?

Separation of cerebral and pleural ganglia detectable

only internally

external fissures detectable in some species

Free visceral loop ganglia

5

1 (adult)

Scenario for ganglion nomenclature (parentheses indicate fusion)

(cg-plg)-1-2-3-4-5-(plg-cg)

(cg-plg-1)-(2–3)-(4-5-plg-cg) or (cg-plg-1-2)-3-(4-5-plg-cg)