Sagitella dubia ( Støp-Bowitz, 1948 ), KOLBASOVA & SYOMIN & SEMPERE-VALVERDE & TEIXEIRA & CARVALHO, 2025

KOLBASOVA, G. D., SYOMIN, V. L., SEMPERE-VALVERDE, J., TEIXEIRA, M. A. L. & CARVALHO, S., 2025, Holopelagic Annelida from the Red Sea off the Central Saudi Arabian coast, Zootaxa 5632 (1), pp. 1-41 : 24

Sagitella dubia ( Støp-Bowitz, 1948) comb. nov.

( Figs 1 , 11 , 12C–F )

Travisiopsis dubia Støp-Bowitz 1948: 60–61 , Fig. 48 [original description, North Atlantic].– Day 1967: 212, Fig. 9.1 j–k [brief description, South Africa].– Dales 1959: 485 [distribution, South China Sea and Malacca Strait].–Fernández-Alamo 2004: 652–654, Fig. 4 [distribution, eastern tropical Pacific], 2006: 210–215, Fig. 2 [distribution, eastern tropical Pacific].– Fernández-Alamo & Sanvicente-Añorve 2005: 234–236 [distribution, California Current, Pacific].

Material examined. Seven specimens: ZMMU WS20983 , ZMMU WS20984 , ZMMU WS20985 , ZMMU WS20986 , ZMMU WS20987 (Et); ZMMU WS20988 (FA), ZMMU WS20989 (FA, Et) .

Description (based on all our material). Body 2.5–3.2 mm long, 0.4–0.6 mm wide without parapodia, 0.5–0.7 mm wide with parapodia and cirri, with 21–23 chaetigers of body trunk. Depending on amount of food swallowed, body may be slender or thick and fusiform ( Fig. 12C–E ). Live worms semi-transparent; ethanol- and formalin-fixed specimens semitransparent white. Prostomium conical, pointed, with small terminal palpodium. Nuchal organs as two low semicircular ridges on dorsal side of prostomium ( Fig. 12C ). Caruncle is poorly pronounced, semiglobular and not encompassed by the nuchal organs ( Fig. 12C ). Extended proboscis short, funnel-like ( Fig. 12F ). Three anteriormost pairs of cirri oval, covering head region. First pair attached at level of nuchal organs, second pair attached at level of head and neck border ( Fig. 12C ). All chaetigers with dorsal and ventral podial cirri. Podial cirri oval and relatively small, they do not cover lateral sides of chaetigers ( Figs 12E–F ). Parapodia from 3 rd –4 th chaetiger, small, conical, uniramous, each with two simple recurved capillary chaetae, and one thick aciculum penetrating through epidermis. Caudal cirri very large, larger than all podial cirri, oval with opaque middle rib ( Fig. 12D ).

Distribution. Type locality: North Atlantic, Gulfstream, 39.50° N, 49.70° W ( Støp-Bowitz 1948). Later records of Sagitella dubia comb. nov. include: tropical and subtropical Atlantic, Indo-Pacific; Central Red Sea (this study).

Remarks. This species was described by Støp-Bowitz (1948) as Travisiopsis dubia . However, the author himself had doubts about referring this species to the genus Travisiopsis which is reflected in the species name “ dubia ” and is commented on in the original paper: “ In spite of the shape of body resembling more a Sagitella I refer this species to the genus Travisiopsis because of the possession of a caruncle, and the size of the caudal cirri.” ( Støp-Bowitz 1948). Nevertheless, both 18S and 28S markers cluster this worm together with S. kowalewskii . Therefore, we emended the diagnosis of Sagitella by deleting the absence of caruncle.

Sagitella dubia comb. nov. differs from S. kowalewskii by the location of cephalic cirri. While S. kowalewskii has the 1 st pair of cephalic cirri almost at the base of the palpodium, and the 2 nd pair at the level of the nuchal organs, in Sagitella dubia comb. nov., the 1 st pair is attached at the level of the nuchal organs, and the 2 nd is attached on the neck ( Fig. 12A and C ). This morphological characteristic is very convenient, since the places where cirri used to be attached are visible even in damaged specimens.

Figures

FIGURE 1. Location of the study area and sampling scheme. Designations: yellow, green and purple circles mark first (12.12.2023), second (18.12.2023) and third (17.04.2024) sampling events, respectively.

FIGURE 2. Krohnia cf. lepidota ZMMU WS20944, general view. (A) anterior end, dorsal view, (B) anterior end, ventral view. Designations: fan–frontal antennae, man–median antenna, dc–regular dorsal tentacular cirri (pairs D1 and D2), ecs–cirrostyle of enlarged dorsal tentacular cirrus (pair D3), ecp–cirrophore of enlarged dorsal tentacular cirrus (pair D3), vc–ventral tentacular cirri, dcp–cirrophore of dorsal parapodial cirrus, vpc–ventral parapodial cirrus. Small black arrowheads point at brown dots, big white arrowheads point at segmental glands. A and B to same scale.

FIGURE 4. Bayesian tree inferred from concatenated 18S and 28S sequences obtained from our Alciopini material and from GenBank. Black numbers above branches indicate Maximum Likelihood bootstrap values; blue numbers below show Bayesian posterior probabilities. IDs of specimens collected in the Red Sea during the present study marked by blue boxes.

FIGURE 9. Relationships of Pelagobia longicirrata from the Red Sea (ZMMU WS20993) with other Pelagobia species (data from GenBank) using the 18S gene marker. Black numbers above branches indicate Maximum Likelihood (ML) bootstrap values; blue numbers below show Bayesian posterior probabilities (BI). ID of the specimen collected in the Red Sea during the present study marked with blue box.

FIGURE 11. Typhloscolecidae from the Red Sea. Maximum Likelihood tree inferred from concatenated 18S and 28S sequences obtained from our material and from GenBank. Black numbers above branches indicate Maximum Likelihood (ML) bootstrap values; blue numbers below show Bayesian posterior probabilities (BI). IDs of specimens collected in the Red Sea during the present study marked with blue boxes.

FIGURE 12. Typhloscolecidae. (A) Sagitella kowalewskii, anterior end, (B) posterior end, (C) Sagitella dubia comb. nov., anterior end, ZMMU WS20989 (D) posterior end, ZMMU WS20989 (E) general view of a “thick” worm, ZMMU WS20984, ZMMU WS20985, ZMMU WS20988 (F) anterior end, ventral view. Designations: cr—caruncle, no—nuchal organs, pb— proboscis, pd—palpodium, I—first cephalic cirrus, II—second cirrus, III—third cirrus. Black arrowhead indicates the place of attachment of the first cephalic cirrus, Sagitella kowalewskii has the second pair of cirri attached at the level of nuchal organs, Sagitella dubia comb. nov. has the first pair of cirri attached at the level of nuchal organs and the second pair on the neck.