Haplotaxidae Michaelsen, 1900

Martin, Patrick, Fend, Steven, Martinsson, Svante, Klinth, Mårten, Torii, Takaaki & Erséus, Christer, 2024, Towards an integrative revision of Haplotaxidae (Annelida: Clitellata), Zoological Journal of the Linnean Society (zlae 141) 202 (4), pp. 1-38 : 8

Haplotaxidae Michaelsen, 1900 s.s. (clade 1 in Fig. 1 )

Type genus: Haplotaxis Hoffmeister, 1843

(with type species Lumbricus gordioides Hartmann in Oken, 1819);

Phreoryctes Hoffmeister, 1845 is a junior synonym to Haplotaxis .

Diagnosis [modified from the Haplotaxis description in Brinkhurst (1988)]

Body form narrow and elongate, body wall with well-developed cuticular layer, brain anterior to mouth within elongate peristomium, the latter usually biannulate with a distinct transverse groove, although not in all species ( Brinkhurst and Marchese 1987, Brinkhurst and McKey-Fender 1991) ( Figs 2A–C , 3C ). Ventral chaetae large, single, usually straight in basal part and curved to strongly hooked distally ( Fig. 3I–J ); simple-pointed, but may have distal ornamentation or keel; modified genital chaetae in at least two species. Dorsal chaetae smaller than ventrals, single, sigmoid to nearly straight; may be absent in many or all segments. Foregut without a dorsal, pharyngeal pad; mouth opens into a capacious, thin-walled oral cavity (possibly eversible) ( Fig. 3B–C ); mouth and oral cavity with strongly developed radial muscle bands extending to the body wall, interspersed with diagonal muscle bands ( Figs 2A–C , 3A ); conspicuous pharyngeal glands absent. Oral cavity terminates in a thick-walled, muscular pharynx (or ‘gizzard’, a disputed term here—see ‘Gizzard vs. muscular pharynx in Haplotaxis ’ in the discussion), consisting of transverse-circular muscle bands, interspersed with radial muscle, usually in IV– V ( Fig. 3B–D ). Nephridia present in all middle and posterior segments; ducts with large, irregular cells, forming a compact mass filling much of the segment ( Fig. 3G ). Conspicuous coelomocytes absent. Dorsal and ventral blood vessels connected by simple commissural vessels, often in each segment; those in anterior segments long and convoluted. Small clusters of glandular cells (‘Timm’s glands’) may be present midventrally in some segments, approaching or surrounding the ventral nerve cord ( Fig. 3H ). Clitellum one cell thick. Spermathecae in 2–4 segments, in front of gonadal segments, typically petiolate, with pores anterior and lateral or dorsolateral. Usually with two pairs of testes (typically in X– XI), followed by one or two pairs of ovaries with the second pair rather than the first being lost where reduction has occurred; eggs mesolecithal. Gonoducts simple, without attached prostate glands, but there may be glands around the pores; male ducts tubular, plesioporous.

Figures

Figure 1. Phylogenetic tree of Clitellata estimated with Bayesian inference in MrBayes, using a concatenated set of markers, i.e. 12S, 16S, COI, 18S, and 28S. The tree is rooted such that Parvidrilidae and Randiellidae (also Clitellata) appear as lineages outside the rest of the ‘Clitellata’ tree, a position strongly supported by the metagenomic analyses of Erséus et al. (2020). Haplotaxid like taxa are shaded.Support values at branches are posterior probabilities, scale represents expected number of changes/site. Capital letters at the end of the species codes in Haplotaxis indicate countries of origin.BEN: Benin, FR: France, GR: Greece, IT: Italy, JP: Japan, SE: Sweden, US: USA. Inset, photo of live specimen of Haplotaxis spSE in its natural habitat, soil soaked in groundwater, photo: Johan Wingborg, and photo of live specimen of Haplotaxis spBEN6, photo: Patrick Martin.

Figure 2. Comparison of anterior ends of haplotaxid-like worms analysed here, schematic figures with emphasis on somatic characters. C, F, and H are from the genetically analysed specimens, the other figures are based on individuals from the same site (and usually same date) as the analysed worms, but better fixed for morphology. A, Haplotaxis spUS2 from Corral Creek, Idaho, USA.Oral cavity of gut is contracted, muscular pharynx extends through two segments.B, Haplotaxis spJP2 from Gudari-numa, Aomori, Japan.Oral cavity of gut is expanded, muscular pharynx is shorter than in the Idaho specimen. C, Haplotaxis spJP1 from Kakida River, Shizuoka, Japan.Timm’s glands are larger than in (A) or (C), muscular pharynx is short.D, Haplotaxoides decipiens from Guadalupe Creek, California, USA.E, Ohtakiana kakidaensis from Kakida River, Shizuoka, Japan. F, Pelodrilus cf. darlingensis from Western Australia. G, Limpluvia setoensis from Asahina River, Shizuoka, Japan. H, undetermined Lumbriculidae, specimen CE32192, from Euchre Creek, Oregon, USA.

Figure3.Haplotaxis species,somaticcharacters.A,Haplotaxis spUS2 fromCorral Creek,Idaho,USA.B,D–H,unidentifiedHaplotaxis sp.(population notanalysed genetically) fromsprings near Brewer,Montana,USA.C, I, Haplotaxis spUS3from Guadalupe Creek,California,USA.J,unidentified Haplotaxis sp.(population not analysedgenetically) from StonyCreek,California,USA.A, anteriorend ofdissected worm,showing extensive musculaturebetween gut and bodywall in I–III,and thick-walledmuscular pharynx in IV–V.B,sagittal section,showingthin-walled oral cavity (right, anterior) and contracted,muscular pharynx (left,posterior).C, wholemounted worm, showingpartially contracted oral cavity and muscular pharynx, and secondary annulationbeginning in V.D,sagittal section ofa contracted muscular pharynx,with central band ofcircularmuscles,surrounded by region with more radial muscles.E, F,sagittal sections ofmiddle and posterior regions showing gut wallwith extensive chloragogen layer.G, sagittal section oftwo middle segments showingextensive nephridia.H, sagittal section,showing Timm’sgland beneath ventral nerve cord.I, smalldorsal and large ventral chaeta (with a partially developedventral chaeta) in mid-bodysegment.J,ventral chaeta frommid-body segment.