Thelepus marthae, Jirkov, Igor, 2018

Jirkov, Igor, 2018, Three new species of Thelepus Leuckart, 1849 from Europe and a re-description of T. cincinnatus (Fabricius, 1780) (Annelida, Terebellidae), ZooKeys 759, pp. 29-56 : 29

Thelepus marthae sp. n. Figs 6, 7, 11C

Thelepus cincinnatus : Zatsepin 1948: 154, table XXXVIII, 7 (partim); Jirkov 2001: 526-527 (partim) - non Fabricius 1780.

Material

(Table 1): 921 specimens from 38 stations collected from depths between 95-1,510 m, bottom temperature -1.84-2.8 °C. Holotype: R/V Tunetz cruise 105 station 6. Material is deposited at the KGB, fifteen paratypes from Alaid st. 6 are deposited at MNCN 16.01/17773, seven paratypes are deposited at ZIN 1/33266.

Description

(based on holotype and paratypes). Holotype with 81 segments, 55 segments with notopodia, 55 mm length. Paratypes up to 80 mm in length, 6-7 mm in width, 100 segments, last segments still in formation and clustered, not fully developed, with poorly-developed neuropodia, so not possible to count total number of segments.

Several tens of buccal tentacles, their length in fixed specimens equal to half of body length. Eyespots absent (Fig. 6 A–C). BS1 with up to ten filaments (seven in holotype); BS2 with up to five (four in holotype) (Fig. 6F, H). Number of filaments increases with worm size; smallest worms, width <1 mm, with either no branchiae or with 1-2 filaments on BS1 and none on BS2. However, maximum number of filaments constant in different samples (containing sufficient worms) despite a range of maximum worm sizes across the samples. For example, largest worms from sample SP-22 st. 60 are at least three times larger than those from sample Alaid st. 3, but maximum number of filaments observed is same. Branchial filaments of BS1 extend laterally from level of notopodia of C1, to a maximum level with upper margin of uncinal row of U1. Filaments attached in a single row on an elevated stump. A wide medial gap separates left and right groups of filaments. Lateral lobes absent. Barely visible nephridial papillae on S4-S7 above neuropodia (Fig. 6A, B arrowed), in most specimens, few papillae visible, usually none. Ventrum glandular, with “wrinkling” (Fig. 4B) increasing with worm size (Fig. 6G).

Notopodia from S3, anterior notopodia almost cylindrical. Notopodia on C1, often C2, and sometimes C3 two to three times smaller than most developed notopodia (app. C10), sometimes one notopodium on C1 absent (Sevastopol 1358). Most developed notopodia transversally flattened, then reduced in size and become cylindrical again. In the most posterior segments notopodia very small; notochaetae present but several times shorter than most developed ones with no more than 10 per ramus; neuropodia also reduced to small pinnuli with few uncini. Notochaetae absent in 20-40 developing segments near pygidium (Fig. 6E); exact number difficult to determine as both annulation and neuropodia poorly developed. Some specimens also without notopodia on the 10-20 preceding reasonably well-developed segments. Number of segments with notopodia around 60 (in few complete worms available for this species), with several posterior segments lacking notopodia. However, segments without notopodia form only ca. 10% of the total worm length. Notochaetae of anterior segments two to three times longer than notochaetae of posterior segments. Notochaetae in two transverse rows: anterior row with short chaetae, distal half (winged part) becomes stained with methylene blue, posterior row with long chaetae. Notochaetae with narrow brims (Fig. 11C).

Neuropodia from C3; tori increasing in size to U10, then becoming progressively slightly shorter. Uncini in single row. Uncini of U1 with well-developed prow and crest with one tooth in profile (Fig. 7A, C–E), posterior uncini (U20 from pygidium) very similar (Fig. 7B).

Pygidium with crenulated margin without cirri or papillae (Fig. 6E).

Differential diagnosis.

Only one previously known species, T. pascua (Fauchald, 1977) from the Caribbean coast of Panama, has two pairs of branchiae and no eyespots. It differs from T. marthae in the lower number of branchial filaments: single filament in BS1 and BS2 in T. pascua ; up to 20 filaments in BS1 and up to 10 filaments in T. marthae . Thelepus marthae differs from T. davehalli (described above) in the typically observed absence of fully developed segments without notopodia; if present, they form no more than 10% of the body length. Thelepus marthae differs from T. crassibranchiatus Treadwell, 1901, T. hamatus Moore, 1905 and T. pascua (Fauchald, 1977) (which have eyespots) in the higher number of branchial filaments and segments with notopodia. Thelepus marthae differs from T. cincinnatus and T. antarcticus in the lower number of branchial filaments and segments with notopodia. Thelepus marthae differs from T. parapari in the shape of its uncini.

Remark.

One specimen (SP-22 st. 72) has numerous spots (Fig. 6D); together forming a transverse row, as with typical eyespots but, in this case, each individual spot is longitudinal instead of rounded as in T. cincinnatus (Fig. 2B) and other Terebellidae . These spots are in the same place as eyespots, but their very unusual shape makes their interpretation as eyespots doubtful; other interpretations are possible.

Etymology.

Species is named after my friend Dr. Martha K. Leontovich (Fig. 8); she has described several new terebellid species.