Lumbricillus Orsted , 1844

Klinth, Marten J., Rota, Emilia & Erseus, Christer, 2017, Taxonomy of North European Lumbricillus (Clitellata, Enchytraeidae), ZooKeys 703, pp. 15-96 : 18-19

Lumbricillus Orsted, 1844

Genus description/diagnosis.

Mainly red, pink, orange, yellow or white when alive, sometimes green or black. Living worms ranging from about 5 to 20 (35 in extremes) mm, fixed from 3 to 14 mm (35 mm in L. maximus (Michaelsen, 1888) even after fixation; Rota 2001). Prostomium hemispherical. Head pore at 0/1. Epidermis with transverse rows of gland cells. Chaetae usually sigmoid, sometimes straight, without nodulus, upper bundles varying from a dorsolateral to a midlateral position. Oesophageal appendages absent. Pharyngeal glands in three pairs, located in IV–VI, usually converging dorsally, sometimes connected dorsally, usually with ventral lobes, but secondary glands absent. Only nucleated coelomocytes present. Dorsal vessel originating intra- or in a segment posterior to clitellum. Nephridia with anteseptale made up of funnel only. Clitellum covering XII-XIII, sometimes also extending over parts of XI. Testes surrounded by peritoneal sacs; the latter usually made up of large lobes arranged in a regular bunch, in some smaller species forming a compact mass, only slightly and irregularly lobed. Penial bulbs round and compact, in a few species bilobed. Midventral subneural glands usually present in XIII–XV, sometimes further back. Spermathecae in V, sometimes extending further back, attached to and usually communicating with lumen of oesophagus; glands surrounding ectal part of ectal duct, sometimes also along ectal duct. Spermathecae either club-shaped with ampulla distinctly set off from duct or spindle-shaped without clear distinction between ampulla and duct. Spermathecal diverticula absent. Mainly living in the littoral zone of the sea but some species also found in limnic and/or terrestrial habitats.

Type species.

Lumbricus lineatus Müller, 1774.

Other species.

See Table 1 and notes below.

Remarks.

Based on the recent phylogenetic analysis of North European Lumbricillus , a number of monophyletic groups within the genus were recognized ( Klinth et al. 2017). Several of these are distinguished by a combination of morphological characters that we refer to when discussing the taxonomy below. For convenience, we informally divide the species investigated into five groups based on their morphology: the lineatus group, the pagenstecheri group, the buelowi group and the arenarius group, all molecularly monophyletic, and the " tuba " group, which is molecularly paraphyletic (thence the quotation marks) (see Klinth et al. 2017) (Table 1, Fig. 1). The lineatus , pagenstecheri and " tuba " groups all have testis sacs with several large lobes in a bunch-like arrangement, characteristic for the majority of Lumbricillus species. The testis sacs of the buelowi and arenarius groups appear as a more or less compact irregular mass, which can still be lobed but not bunch-like. Interestingly, we noted that in the former three groups the upper and lower chaetal bundles are arranged almost symmetrically around the body (as dorsolateral and ventrolateral bundles), whereas in the buelowi and arenarius groups the upper bundles tend to be closer to the lateral lines (observed by all three authors). The number of chaetae varies within each group and is usually 3-6 in each bundle but can reach 10 or more, except in the buelowi and arenarius groups where there are rarely more than 2-3 chaetae per bundle. The length/width ratio of the sperm funnels varies within and among the species in each group, but the funnels are usually only a few times longer than wide in all groups except for the lineatus and arenarius groups, where they can be 5-10 times longer than wide. The penial bulbs are round and compact in all groups except the arenarius group where they can also be bilobed. Finally, the spermathecae are spindle-shaped without a clear distinction between the ectal duct and the ampulla in the lineatus group; have a clear distinction between ectal duct and ampulla in the pagenstecheri , " tuba " and buelowi groups, with gland cells also along the duct in the pagenstecheri group; or have a gradually widening ectal duct, making the ampulla more or less indistinct in the arenarius group (Table 1, Fig. 1). Using these combinations of characters we made a preliminary placement of the remaining Lumbricillus species, not studied in this paper, into any of these five groups (Table 1). Note that, as we have not been able to include these species in our molecular phylogeny, we cannot be certain that our species groups would remain monophyletic with the addition of these species.