Lumbriculidae

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 : 30

Lumbriculidae gen. sp. (genus undetermined)

( Figs 2H , 10 )

Material examined: USNM 1716322: an immature worm, anterior end whole mounted, part of tail analysed for DNA (CE32192), COI DNA-barcode in GenBank (acc. no. PP988429); for other molecular data, see Table 1 .

Locality: USA: Oregon, Curry Co., Euchre Creek, near Ophir , 10 Jul 2017 .

Description

Habitus thin, elongate, appearing similar to Haplotaxis specimens in the same sample; 100 segments remain, estimated to be 1/2 of the original worm. Diameter 0.32 mm on slide. Prostomium longer (260 μm) than wide (190 μm); peristomium not elongate ( Fig. 2H ). Chaetae paired, simple pointed, sigmoid; ventrals 111–126 μm long, 5–7 μm thick, nodulus 0.33– 0.37 the chaetal length from tip; dorsals 84–94 μm long, about 3 μm thick, nodulus 0.33–0.42 the chaetal length from the tip ( Fig. 10A ). Pharynx not strongly developed, about equally thickened dorsally and ventrally, without conspicuous musculature; no obvious pharyngeal glands. Chloragogen on gut beginning in about XV, becoming progressively more developed posteriorly, very dense from about XXXV. Midventral glands beginning in V, strongly developed from X posteriad ( Figs 2H , 10B ); each segment with a cluster of densely packed, petiolate multicellular glands about 50–60 μm high, interspersed with circular muscle strands of body wall; glands extend up to ventral nerve cord, but do not surround it (as in Timm’s glands). Gland clusters about 130–150 μm wide. Additional large cells are loosely associated with septa in ventral part of coelom; cells are about 10–25 μm wide, irregular and highly granular.

Remarks

This unidentified lumbriculid was originally considered a possible haplotaxid, based on its unusually elongate body form, enlarged ventral chaetae, midventral glands, and the pharynx lacking a dorsal pad or conspicuous pharyngeal glands. The single sequenced specimen was preserved in ethanol, and middle segments were used for DNA analysis—thus limiting descriptive detail. Although the specimen is immature, it clearly represents an undescribed species.

Specimens similar in general appearance, with similar pharynx, chaetae, and midventral glands have been collected at several other sites in Pacific coastal streams from California and Oregon. The granular, irregular cells associated with the septa in the sequenced worm may be glandular tissue, but as they were not observed in specimens from other collections, an alternative possibility is that they represent some kind of parasite.

The gut of the sequenced specimen appeared empty, but of 37 morphologically similar specimens from streams in western North America, 13 contained oligochaete chaetae (lumbriculids, Nais , Mesenchytraeus ), and two contained a chironomid head. Guts of most of the remainder were empty or contained small amounts of stream sediment (in less than 10% of segments). As in the case of haplotaxids, only immature specimens have been found at most sites. Two mature individuals from central California could not be sequenced, but arrangement of their reproductive organs resembles that of the genus Stylodrilus Claparède, 1862 .

Figures

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.

Figure 10. Undetermined Lumbriculidae sp., Euchre Creek, Oregon, specimen CE32192. A, chaetae, from left to right: a ventral and dorsal chaeta from XX; a ventral pair and dorsal chaeta from XL; a ventral chaeta from the posterior segment. B, midventral gland and chaetae in XX, with unknown cells on septa.