Haplotaxoides decipiens Fend, 2024

Haplotaxoides decipiens Fend View in CoL sp. nov.

( Figs 2D View Figure 2 , 4 View Figure 4 , 5 View Figure 5 )

ZooBank LSID: urn:lsid:zoobank.org:act:C869EC41-8CBB-4463-AF37-3515C8C9F982

Synonyms:

Haplotaxis cf. gordioides View in CoL ; Erséus and Källersjö (2004: table 1); Rousset et al. (2007: table 1); Erséus et al. (2010: table 1).

Holotype: USNM 1716307 : a partially mature worm (with developing gonads), anterior end whole mounted, posterior end analysed for DNA (CE30888); COI DNA-barcode in GenBank (acc. no. PP988425 ) GoogleMaps ; for other molecular data, see Table 1 View Table 1 .

Type locality: USA, California, Santa Clara Co., Guadalupe Creek above reservoir   GoogleMaps , 37.18237° N, 121.87236° W, in cobblegravel bed, 15 May 2016, collected by S. Fend.

Paratypes: USNM 1716308–1716311 About USNM , 1716313 About USNM , from the type locality: 15 May 2016, an immature worm, whole mounted anterior end, posterior end analysed for DNA ( CE30889 ), COI DNA-barcode in GenBank (acc. no. PP988426 ), for other molecular data, see Table 1 View Table 1 . 8 April 2007, a partially mature whole mount. 25 March 2007, two partially mature whole mounts. 23 June 2011, an immature whole mount. USNM 1716312 About USNM : USA, California, Santa Clara Co., Los Gatos Creek above Aldercroft Heights , 37.1478° N, 121.9562° W, 26 May 1998; a partially mature whole mount. GoogleMaps

Other material: SMNH 108431 View Materials : USA, California, Santa Clara Co., Los Gatos Creek above reservoir, 26 May 1998; a partially mature worm, anterior end whole mounted, posterior end analysed for DNA (CE438) ; for molecular data, see Table 1. S View Table 1 . Fend collection: California, Santa Clara Co., the type locality 25 Mar 2007; three whole mounts. 8 Apr 2007 ; three whole mounts. 11 May 2008 ; three whole mounts. 24 Mar 2011 , two whole mounts. 20 Jun 2011 ; three whole mounts, two sagittally sectioned. 26 May 2012 ; two whole mounts. 21 Jun 2014 ; four whole mounts. Los Gatos Creek above reservoir, 9–26 May 1998 ; 23 whole mounts, one dissected. Rincon Creek near confluence with Guadalupe Creek, 5 Sep 2000 ; one whole mount. All collected by S. Fend.

Etymology

Named decipiens (Latin for ‘deceiving’), as it was originally assumed to be a Haplotaxis species, based on general morphology. In this study, we included the specimen ( CE 438) identified as Haplotaxis cf. gordioides by Erséus and Källersjö (2004), but now found to be Haplotaxoides decipiens .

Description

The primary description is based on specimens from the type locality and nearby tributaries (Los Gatos and Rincon Creeks) to the Guadalupe River , Santa Clara Valley, California. No fully mature specimens were available for study; measurements in the description are based on partially mature specimens with well-developed testes and sperm morulae, and with small ovaries .

Length 26–58 mm, diameter in X 0.25–0.41 mm, maximum diameter 0.28–0.47 mm, 142–220 segments ( Fig. 5A View Figure 5 ). Secondary annulation beginning in V, an anterior ring about 1/4–1/3 segment length, may be strong or indistinct in middleposterior segments of fixed specimens.

Chaetae single in dorsal and ventral bundles from II; all with a distinct nodulus 0.35–0.5 the chaetal length from the tip. Dorsal chaetae ( Fig. 4A View Figure 4 ) slightly sigmoid, simple-pointed, length 65–90 μm, diameter 3–5 μm. Ventral chaetae ( Figs 4A View Figure 4 , 5F View Figure 5 ) larger, increasing in length from 60–70 μm in anterior segments, to 130–180 μm in middle and posterior segments, diameter 9–11 μm, with a straight basal shaft and strongly arcuate distal part, tip may have small dorsal keel, or may be simple-pointed (perhaps from wear).

Cuticle thick,about5–6 μm throughout ( Fig.5E View Figure 5 ).Prostomium demarcated posteriorly by transverse groove, longer (205–250 μm) than wide (135–205 μm), with epidermis 18–25 μm thick, transverse muscle layer 8–12 μm thick, inside thinner longitudinal muscle layer ( Figs 4I View Figure 4 , 5B View Figure 5 ). Peristomium with thin, irregular epidermal layer (6–12 μm); transverse muscle fibers of body wall thinner than in prostomium. Segments from II and posterior with thin, irregular, and often indistinct epidermis, cells interspersed with fibres of thin circular muscle layer, the combined layer about 10–12 μm in anterior segments, thinner posteriorly; longitudinal muscle layer 10–20 μm thick in anterior and middle segments. Brain at anterior margin of peristomium, at transverse groove ( Figs 4I View Figure 4 , 5B View Figure 5 ); ventral nerve cord flanked by two thick, glandular pads in each segment beginning in II ( Fig. 4G View Figure 4 ). Septa thin in first few segments, but thick beginning at 4/5.

Anterior foregut a buccal-pharyngeal cavity with thickened dorsal wall in I–II, the thin epithelium surrounded by a muscular mass formed by small bundles of transverse fibres interspersed with strong bands anchoring it to the dorsal body wall, and an indistinct layer of thinner, longitudinal muscles ( Figs 2D View Figure 2 , 5C, D View Figure 5 ); ventral area thinner, but with similar musculature. A weak continuation of radiating muscle bands extending from mid-II to mid-III; circular muscles forming a weak sleeve surrounding gut in III ( Figs 2D View Figure 2 , 4I View Figure 4 , 5C–E View Figure 5 ); no pharyngeal glands. Gut wall thin and uniform beginning in mid-III ( Fig. 5M View Figure 5 ), epithelial cells gradually becoming somewhat granular and taller in mid-body; gut epithelium thicker, irregularly folded, and distinctly granular (similar to chloragogen) posterior to about LXX ( Fig. 5N–O View Figure 5 ). Cuticle thick in the first 1/3 of the muscular buccal region, then gradually thins until it is barely perceptible within the region of the circum-pharyngeal muscle ring. Chloragogen layer thin or not apparent on gut in post-gonadal segments. Anus terminal.

Coelomocytes numerous throughout body, oval, 10–15 μm long ( Fig. 5I View Figure 5 ). All segments beginning in III with a cluster of mostly transparent, elongate-sacciform glands inserting midventrally on the body wall between ventral chaetae ( Figs 4F, G View Figure 4 , 5H, I View Figure 5 ); glands usually 3 (2) per cluster, 120–250 μm long, 40–70 μm wide in mid-body. Similar, but much smaller glands visible in I and/or II in some specimens. Cell structure of glands is obscure in most specimens, but in others, each gland appears to be composed of several elongate cells with ental nuclei and narrowing ectally; glands sometimes with an irregular lumen. Glands join at the epidermis in adjacent secretory disks, each with 6–10 apparent cell termini at the surface ( Fig. 5J, K View Figure 5 ). Cells somewhat resemble nephridial tissue, but vary histologically; typically, 2 glands in each cluster appear somewhat granular, and the third is more transparent. Nephridia paired; small in VII –XV( XVI), then larger from about XVI through remaining segments. In middle to posterior segments a small (25–30 μm long) anteseptal funnel leads to a thick (30–35 μm) nephridial duct that extends up to above gut, folding back on itself to form an irregular mass filling much of the segment ( Figs 4H View Figure 4 , 5G View Figure 5 ), and ending in a thinner duct terminating in an inconspicuous nephridiopore just anterior to the ventral chaeta. Nephridial tissue with large, irregular cells, mostly indistinct and transparent, but usually containing some darkly granular tissue in ental part.

Dorsal blood vessel forks at brain, the two branches then enter prostomium, turn back around the mouth, and join in III to form ventral vessel. Lateral, commissural blood vessels long and convoluted, prominent in anterior segments, thinner and adjacent to posterior septa in middle and posterior segments.

Spermathecal pores not obvious in partially mature worms; cell clusters that may be partially developed spermathecae visible anterior to dorsal chaetae in V – VIII in 14 specimens having dense sperm morulae both in testicular segments and in small sperm sacs extending as far back as XIV ( Fig. 4F View Figure 4 ).

Testes in XII – XIII, sperm morulae fill both segments in several partially mature specimens, extending posteriad within small sperm sac ( Fig. 5L View Figure 5 ); partially developed male funnels on posterior septa of testicular segments, but sperm ducts not developed. Ovaries of most partially mature worms in XV only, female funnels not developed.

Remarks

The thicker integumental cuticular layer (4–7 μm) may be the most consistent character separating Haplotaxoides decipiens from Haplotaxoides tehama sp. nov. (see below, 2–3.5 μm), although body dimensions and size of ventral chaetae were also generally greater. As mature Haplotaxoides decipiens specimens were not available, there is little basis for separating this species from Haplotaxoides tehama using the usual morphological characters related to reproductive organs. The dorsal cell clusters seen in segments V – VIII of partially mature Haplotaxoides decipiens are in a position similar to that of spermathecae in other haplotaxid-like oligochaetes, and thus may be either developing spermathecae or some unknown type of gland. No such organs were observed in the two mature Haplotaxoides tehama specimens (see below), or in any of the immature ones.

Site descriptions

Collection sites on Guadalupe and Los Gatos are small, low order streams in a densely forested landscape; with cool water, supporting native salmonids; benthic fauna at both sites is dominated by pollution intolerant insects (Carter and Fend 2000). The Los Gatos Creek site has permanent streamflow, due to upstream reservoir releases. Streamflow at the unregulated Guadalupe Creek site is intermittent in some years, with little or no surface flow in summer; but subsurface flow contributes to low temperatures in scattered permanent pools. Haplotaxoides decipiens was generally found in gravel patches within cobble-boulder riffles. The Los Gatos Creek site is the type locality for the lumbriculid Eremidrilus felini Fend & Rodriguez, 2003 , and the Guadalupe Creek site is the type locality for the rhyacodriline naidids Rhyacodrilus alcyoneus Rodriguez & Fend, 2013 and Rhyacodrilus longichaeta Rodriguez & Fend, 2013 .