Laeonereis pandoensis ( Monro, 1937 )

Conde-Vela, Víctor M., 2021, Revision of Laeonereis Hartman, 1945 (Annelida: Phyllodocida: Gymnonereidinae), with a review of shaft morphology in nereidids, Journal of Natural History 55 (7 - 8), pp. 381-455 : 428-433

Laeonereis pandoensis ( Monro, 1937)

( Figures 5 (b,k), 6, 22(a–g), 23(a–i), and 24(a–n))

Leptonereis pandoensis Monro 1937: 242–246 , figs 1a, 1b, 1c, 1d, 1e, 1f.

Laeonereis pandoensis Hartman 1948: 56 . Orensanz and Estivariz 1971: 99–101, fig. 10–22.

Type material

Southwestern Atlantic Ocean, Uruguay. Syntypes of Leptonereis pandoensis USNM 43474 and BMNH 1937.4.22.4–30 (29), Arroyo de Pando, Canelones, South America, in fresh water, Coll . E .H. Cordero.

Additional material

Southwestern Atlantic Ocean, Argentina. ECOSUR-P3103 (55), Playa Cenpat, Puerto Madryn, sandy bottom, 26 February 2013, Coll. J.M. Orensanz, E. Diez, B. Trovant, S.I. Salazar-Vallejo.

Description

Syntype (USNM 43474) complete, 42 mm long, 1.8 mm wide at chaetiger 10, 115 chaetigers ( Figure 22 (c,f)); two other syntypes (BMNH 1937.4.22.4-30) complete, in good condition ( Figure 22 (a,b)). Non-type specimens ( ECOSUR-P3103 ) from Argentina in good condition, one selected for description, complete, 25 mm long, 1.4 mm wide at chaetiger 10, 69 chaetigers ( Figure 22 (d,e,g)) . Body of syntypes pale, no pigmentation observed ( Figure 22 (a–c,f)); body of non-type specimens pale, black spots present on prostomium and dorsal surface of achaetous ring and first chaetigers, disappearing towards posterior end ( Figure 22 (d,e,g)).

Prostomium hexagonal, wider than long, anterior margin shallowly cleft and almost inconspicuous, dorsal groove deep and wide and reaching the anterior pair of eyes ( Figure 22 (c–e)); antennae digitiform, 0.5–0.8 times as long as the dorsal groove ( Figure 22 (c–e)); eyes black to reddish, rounded, sometimes anterior pair slightly reniform, the two pairs subequal ( Figure 22 (c–e)). Achaetous ring 1.2 times longer than first chaetigers ( Figure 22 (c–e)); four pairs of anterior cirri, cirrophores conspicuous, longest pair reaching chaetiger 2 ( Figure 22 (c–e)).

Pharynx dissected. Jaws brownish, entire cutting edge dentate ( Figure 5 (k)). Maxillary ring: I = 1–1 tuft of verticillate rod-like papillae; II = 1–1 tuft of verticillate rod-like papillae; III = 3 tufts of verticillate rod-like papillae; IV = 1–1 tuft of verticillate rod-like papillae. Oral ring: V = 0; VI = 1–1 triangular papilla; VII–VIII = one ridge row with 5 rounded papillae, 1 papilla on each A–C region. Caecal glands absent ( Figure 5 (b)).

Pattern of pedal glands ( Figure 6 ). UpG subconical and shorter than MeG in anterior chaetigers, splitting into two or three smaller glands towards middle chaetigers. LoG oblong and subequal to UpG in anterior chaetigers, disappearing towards middle chaetigers. MeG elliptical and twice larger than PoG in anterior chaetigers, becoming slighty shorter in middle chaetigers. PoG dissapearing towards middle chaetigers.

First two chaetigers with neuroaciculae only, remaining ones with both noto- and neuroaciculae. In first two chaetigers ( Figure 23 (a,g)), dorsal cirri linguiform. Dorsal ligules subconical, blunt, twice as wide as long, 3.5 times longer than dorsal cirri, 1.3 times longer than neuroacicular ligules. Neuroacicular ligules subconical, blunt, 1.5 times wider than long; postchaetal lobes digitiform, as long as wide, 1.3 times longer than dorsal ligule, 1.2 times longer than neuropodial ventral ligules; neuropodial ventral ligules digitiform, twice as wide as long, as long as neuroacicular ligules, twice as long as ventral cirri. Ventral cirri subconical.

In anterior chaetigers ( Figure 23 (b,h)), dorsal cirri linguiform to digitiform. Notopodial dorsal ligules subconical, blunt, 2.5 times wider than long, 4 times longer than dorsal cirri, 3 times longer than prechaetal lobes; prechaetal lobes rounded, as long as wide; notopodial ventral ligules subconical, blunt, as long as wide, 2.2 times longer than prechaetal lobes, 1.3 times longer than neuropodial postchaetal lobes. Neuroacicular ligules subconical, blunt, 1.5 times wider than long; postchaetal lobes digitiform, as long as wide, 1.5 times longer than neuroacicular ligules, 1.5 times longer than neuropodial ventral ligules; neuropodial ventral ligules digitiform, 2.4 times wider than long, 3.2 times longer than ventral cirri. Ventral cirri subconical.

In middle and posterior chaetigers ( Figure 23 (c–e,i–k)), dorsal cirri linguiform. Notopodial dorsal ligules subconical, 1.8–2.0 times wider than long, 5–6 times longer than dorsal cirri; prechaetal lobes absent; notopodial ventral ligules subconical, 1.2 times longer than wide, 1.2–1.5 times longer than notopodial dorsal ligules, 1.5 times longer than neuroacicular ligules. Neuroacicular ligules subconical, 1.2 times longer than wide, sometimes wider than long because of limpness of tissues, 3 times longer than neuropodial ventral ligules; postchaetal lobes absent; neuropodial ventral ligules digitiform, 7 times wider than long, 4.0–4.5 times longer than ventral cirri. Ventral cirri digitiform.

In posteriormost chaetigers ( Figure 23 (f,l)), dorsal cirri linguiform. Notopodial dorsal ligules subconical, 2.5 times wider than long, 3 times longer than dorsal cirri, becoming shorter and disappearing in posteriormost chaetigers; prechaetal lobes absent; notopodial ventral ligules subconical, 1.7 times longer than wide, 1.6–2.0 times longer than notopodial dorsal ligules, 1.5–2.0 times longer than neuroacicular ligules. Neuroacicular ligules subconical, as long as wide, 2–3 times longer than neuropodial ventral ligules; postchaetal lobes absent; neuropodial ventral ligules digitiform, 4.5–5 times wider than long, 4–5 times longer than ventral cirri. Ventral cirri subconical to digitiform.

Notochaetae homogomph spinigers. Neurochaetae homogomph spinigers in supraacicular fascicles, homogomph spinigers and falcigers in sub-acicular fascicles; subacicular homogomph falcigers absent in anterior chaetigers.

Notopodial and neuropodial homogomph spinigers ( Figure 24 (a–e,g–l)) pectinate, proximal teeth coarse, remaining ones minute, teeth decreasing in size towards distal end; blades of neuropodial supra-acicular spinigers 2.0–2.5 times longer than blades of sub-acicular ones. Neuropodial homogomph falcigers ( Figure 24 (f,m,n)) pectinate, distal tooth stout and hook-like; blades 15 times longer than wide in anterior chaetigers, becoming 19–20 times longer than towards posterior chaetigers ( Figure 24 (f,m,n)). Neuropodial homogomph spinigers present in middle and posterior chaetigers only.

Pygidium funnel-shaped ( Figure 22 (f,g)); anal cirri cirriform, 1.5 times longer than width of pygidium ( Figure 22 (f,g)).

Remarks

Monro (1937) noted parapodial and chaetal differences among the specimens described and the diagnosis for the genera Tylonereis Fauvel, 1911 , Tylorrhynchus Grube, 1866 and Gymnorhynchus Horst, 1918 (now Gymnonereis Horst, 1919 ), but no clear explanation of the decision to place the species into Leptonereis was given, even after he found papillae in the pharynx. The current description agrees well with the original one and the description based on Argentinean specimens by Orensanz and Estivariz (1971), differing only in the following features: the authors determined the dorsal groove of the prostomium is absent, but the examined specimens have a dorsal groove. Monro (1937) and Orensanz and Estivariz (1971) also noted that chaetae in anterior chaetigers consist of homogomph spinigers only in this species, a feature that is shared with all Laeonereis species.

Laeonereis pandoensis is closely related to L. acuta , but de Jesús-Flores et al. (2016) and de León-González et al. (2017) highlighted the following differences: L. pandoensis has several spots of brown pigment on the anterior end of the body, usually forming a striated pattern, whereas in L. acuta the pigment spots are absent; and in L. pandoensis , the longest anterior cirri reach chaetiger 1, whereas in L. acuta they reach chaetiger 5. The pigmentation pattern is useful as a diagnostic feature, but the relative lengths of the anterior cirri overlap in the two species. Further differences are focused on the middle and posterior chaetigers: L. pandoensis has a very wide and deep dorsal groove, 1.5 times wider than the width of the base of the antennae, and the anterior margin of the prostomium is shallowly cleft, whereas in L. acuta the dorsal groove is half as wide as the base of the antennae, and the anterior margin is deeply cleft; in middle and middleposterior chaetigers of L. pandoensis , notopodial ventral ligules are longer than notopodial dorsal ones, whereas in L. acuta the two ligules are subequal; in middle chaetigers of L. pandoensis , the notopodial ventral ligules are 4.0–4.5 times longer than ventral cirri, whereas in L. acuta they are 5–6 times longer; in posterior chaetigers, notopodial dorsal ligules of L. pandoensis are 1.8–2.0 times wider than long, whereas in L. acuta they are 2.3 times wider; in posterior chaetigers, the neuroacicular ligules of L. pandoensis are 2–3 times longer than neuropodial ventral ligules, whereas in L. acuta they are 1.5–2.0 times longer. Both notopodial and neuropodial homogomph spinigers in the syntype of L. pandoensis have basal teeth coarser than in additional specimens, but the fact that the illustration of a homogomph spiniger by Monro (1937, fig. 1(e)) is more similar to spinigers found in additional material than to those in the syntype, and the fact that some teeth are detached, suggest that the teeth in these chaetae are damaged. The length and shape of neuropodial homogomph falcigers are quite similar in L. pandoensis and L. acuta . The blades of the falcigers found in the syntypes of L. acuta become narrower distally, but Monro (1937, fig. 1(f)) figured a falciger with a similar blade shape; finally, the blades found in additional materials of both species are almost identical in shape and length.

Laeonereis pandoensis also resembles L. brunnea in having brown pigmentation in the anterior end, but the two species can be separated as follows: in anterior chaetigers of L. pandoensis , the neuropodial postchaetal lobes are 1.5 times longer than the neuroacicular ligules, whereas in L. brunnea they are as long as the neuroacicular ligules; in the middle and posterior chaetigers of L. pandoensis , the notopodial dorsal ligules are 5–6 times longer than the dorsal cirri, whereas in L. brunnea they are 2.5 times longer; in the middle and posterior chaetigers of L. pandoensis , the notopodial ventral ligules are shorter than the notopodial dorsal ones, whereas in L. brunnea they are longer than or subequal; L. brunnea have neuropodial homogomph falcigers in supra-acicular fascicles, whereas L. pandoensis lacks these chaetae in such fascicles; and the blades of the neuropodial subacicular falcigers in L. brunnea are 10–12 times longer than wide and have serrate, coarse teeth, whereas in L. pandoensis they are 15–20 times longer than wide and have pectinate, minute teeth.

Figures

Figure 5. Foregut, papillae and jaws in Laeonereis species. (a) non-type specimen of L. acuta (ECOSUR- P3102), ventral dissection; (b) non-type specimen of L. pandoensis (ECOSUR-P3103), dorsal dissection; (c) and (d) rounded papillae in area VIII from paratype of L. orensanzi comb. nov. (UANL 7840); (e) rodlike, verticillate papillae from syntype of L. culveri from area IV (USNM 541); (f) everted pharynx from paratype of L. longula sp. nov. (USNM 1490792), labels indicate papillae on the pharyngeal areas; (g) left jaw of the paratype of L. brunnea (USNM 43404), dorsal view; (h) left jaw of the syntype of L. culveri (USNM 541), dorsal view; (i) left jaw of the paratype of L. longula sp.nov. (USNM 1490792), dorsal view; (j) left jaw of L. orensanzi comb. nov. (UANL 7840), dorsal view; (k) left jaw of non-type of L. pandoensis (ECOSUR-P3103), dorsal view. Dark areas in (a) and (b) are due to remnants of Shirlastain staining; (f) is stained with methyl green. Scale bars: a, b = 0.5 mm; c–e, j = 25 µm; f–i, k = 0.1 mm. Abbreviations:Es, oesophagus; Jw, jaw; Pa, papilla; Ph, pharynx; Pp, palpophore; Ps, palpostyle.

Figure 6. Arrangement of pedal glands in Laeonereis species. Abbreviations: DoG = dorsal gland; LoG = lower distal pedal gland; MeG = medial pedal gland; PrG = proximal pedal gland; UpG = upper distal pedal gland.

Figure 22. Laeonereis pandoensis (Monro, 1937). (a, b), syntypes of Leptonereis pandoensis (BMNH 1937.4.22.4–30); (c, f), syntypes (USNM 43474); (d–e, g), non-types (ECOSUR-P3103). (a–b) whole specimens, lateral view; (c–e) anterior ends, dorsal view; (f–g) posterior ends, dorsal view. Scale bars: a–c = 1 mm; d–g = 0.5 mm.

Figure 23. Laeonereis pandoensis (Monro, 1937). (a–f), syntype of Leptonereis pandoensis (USNM 43474); (g–l), non-types (ECOSUR-P3103). (a) chaetiger 2, left parapodium; (b) chaetiger 10, left parapodium; (c) chaetiger 30, left parapodium; (d) chaetiger 48, left parapodium; (e) chaetiger 80, left parapodium;(f) chaetiger 102,left parapodium; (g) chaetiger 2, right parapodium; (h) chaetiger 10, right parapodium; (i) chaetiger 30, right parapodium; (j) chaetiger 50, left parapodium; (k) chaetiger 60, right parapodium; (l) chaetiger 66, right parapodium. Scale bars: a–f = 0.2 mm; g–l = 0.1 mm.

Figure 24. Laeonereis pandoensis (Monro, 1937). (a–f), syntype of of Leptonereis pandoensis (USNM 43474); (g–n), non-type (ECOSUR-P3103). (a) notopodial homogomph spiniger, chaetiger 10; (b) supra-acicular homogomph spiniger, chaetiger 10; (c) supra-acicular homogomph spiniger, chaetiger 48; (d) sub-acicular homogomph spiniger, chaetiger 10; (e) sub-acicular homogomph spiniger, chaetiger 48; (f) sub-acicular homogomph falciger, chaetiger 48; (g) notopodial homogomph spiniger, chaetiger 10; (h) notopodial homogomph spiniger, chaetiger 25; (i) notopodial homogomph spiniger, chaetiger 50; (j) supra-acicular homogomph spiniger, chaetiger 25; (k) sub-acicular homogomph spiniger, chaetiger 10; (l) sub-acicular homogomph spiniger, chaetiger 25; (m) sub-acicular homogomph falciger, chaetiger 25; (n) sub-acicular homogomph falciger, chaetiger 50. Scale bars: a–n= 10 µm.