Thelepus tenuis Londoño-Mesa 2009, comb. nov.
Creators: name: Londoño-Mesa, Mario H.
Publisher: name: Zenodo
Year: 2009
Subjects: Biodiversity
Taxonomy
Animalia
Annelida
Polychaeta
Terebellida
Terebellidae
Thelepus
Thelepus tenuis

description: Thelepus tenuis (Verrill, 1900) comb. nov.   
Figures 26 A-G  
 Protothelepus tenuis, Verrill, 1900:662.   
 Euthelepus tenuis, Caullery, 1915:46–47.— Hartman, 1959:505.— Holthe, 1986b:156.   
 Thelepus tenuis, Hutchings & Glasby, 1986:114.   
 Type material: Holotype slide YPM 2864 Bermuda, no more data.   
 Additional material: YPM 97587 (1) Hungry Bay, Bermuda, 15.VIII.1975; in sand.   
 Description: Holotype incomplete, on slide, poor condition; 19 segments, 6mm long, 1.1mm wide (Figs 26A,B). Upper lip short, rounded. Lower lip slightly swollen. Tentacular membrane short, not clearly visible. Eyespots absent. Some tentacles present, short. Ventral shields, branchiae and nephridial papillae unrecognizable (Figs 26C,D). Sixteen pairs of notopodia; notochaetae lanceolate, in two intercalated lengths (Fig. 26E). Thoracic uncini (Figs 26F,G) with dental formula MF:2:1–3; PP and PF absent; Oc slightly convex; Cp with two lines of teeth, the first line with two teeth, larger than those on second row, and as long as one half of MF; Sr narrow; SrP transformed in long rectangular button without visible SrA, place near a rounded AP; AF absent; Bs curved anteriorly and somewhat flat near the PP. Pygidium missing.   
 Staining pattern: This pattern was identified in the additional material. Only dorsal tissue, and ventral shields from the first 5 segments stain deeply (Figs 26B,D). Other structures not stained.   
 Variations: Only one additional specimen was collected and identified by Dr. M.L. Jones. This small specimen is complete, but divided in two pieces. It has 78 segments, 11.5mm long, thorax 4.2mm long, 0.4mm wide, 22 pairs of notopodia. Eyespots absent. Two pairs of incomplete branchiae, first pair missing the right branchia, second pair missing the left one; branchial filaments from segment 2 at least as long as 12 thoracic segments; filaments from segment 3 as long as four thoracic segments. Thirteen ventral poorly defined shields from segment 2, first shield the widest, then decreasing in width. Abdominal uncini with dental formula MF:2:5. Pygidium smooth, last 7–8 segments thinner than the previous abdominal segments. Segments 2–4 stain deeply dorsally as well as the first 3 ventral shields; the rest of structures not stained.   
 Discussion: This species was described by Verrill (1900) as the type species of a new genus Protothelepus Verrill, 1900, allied to Euthelepus, and distinguished mainly because of the presence of a single pair of long branchial filaments arising, doubtfully, from segment 3 (first segment with notochaetae). Later, Caullery (1915) considered the genus to be possibly invalid because, as it has happened in Eugrymaea Verrill, 1900, the number of [segments with] branchiae was not important for establishing terebellid genera. Thus, he considered Protothelepus a junior synonym of Euthelepus. Nevertheless, Euthelepus has lateral lappets on segments 2–3 or sometimes 2–4. Therefore, since Verrill did not mention lateral lappets, Hutchings and Glasby (1986) questionably referred this species to Thelepus. I agree considering this generic placement after a thorough revision and comparison of type and non-type specimens. They have the same type of chaetae and uncini with the same dental formula. Besides, after staining, it is confirmed that the specimen from Bermuda has two pairs of branchiae, as stated by Hutchings and Glasby (1986). Eyespots are absent in both species, although the original description stated its presence.   
 This species is similar to Thelepus crassibranchiatus in having two pairs of single branchial filaments on segments 2–3; nevertheless, T. tenuis has chaetae lanceolate and uncini MF:2:1–5, with long square button on the Sr. Thelepus crassibranchiatus has chaetae paleate and uncini MF:2, with a small square button on the Sr.   
 Type locality: Bermuda.   
 Distribution: Only known from Bermuda.
description: Published as part of Londoño-Mesa, Mario H., 2009, Terebellidae (Polychaeta: Terebellida) from the Grand Caribbean region 2320, pp. 1-93 in Zootaxa 2320 (1) on page 85, DOI: 10.11646/zootaxa.2320.1.1, http://zenodo.org/record/5316176