Ophryotrocha birgittae, Paxton, Hannelore & Åkesson, Bertil, 2011

Paxton, Hannelore & Åkesson, Bertil, 2011, The Ophryotrocha diadema group (Annelida: Dorvilleidae), with the description of two new species, Zootaxa 3092, pp. 43-59 : 49-53

publication ID	https://doi.org/ 10.5281/zenodo.202108
DOI	https://doi.org/10.5281/zenodo.5619582
persistent identifier	https://treatment.plazi.org/id/9D5787CE-FFCA-035B-FF40-36C6E03D4752
treatment provided by	Plazi
scientific name	Ophryotrocha birgittae
status	sp. nov.

Treatment

Ophryotrocha birgittae View in CoL sp. nov.

Figure 1 View FIGURE 1 C; 3G–I; 5; 6A–C; 8; 9; 10; 11; Table 1 View TABLE 1 ; 2

Ophryotrocha View in CoL sp. Qingdao Dahlgren et al., 2001; Heggøy 2007.

Material examined. Type material: holotype ( SMNH T- 8166), complete specimen, 3.2 mm long (20 chaetigers), 0.4 mm wide without parapodia; 10 paratypes ( SMNH T- 8167), 1.9–3.1 mm (13–19 chaetigers); 10 paratypes (AM W.37219), 1.8–3.1 mm long (12–19 chaetigers); cultured from specimens collected in the muddy littoral zone in the harbour of Qingdao, China, by Ragnar Eide, July 1995. Other material: 50 specimens ( SMNH 117236), 0.5–3.1 mm long (5–20 chaetigers); 50 specimens (AM W.37220), 0.5–3.5 mm long (5–23 chaetigers); all specimens complete, measurements from preserved specimens, cultures from same collection; additional live material.

Description. Length of most live adults 3.5–4.5 mm (17–19 chaetigers), maximum length 5.5 mm (23 chaetigers) ( Table 1 View TABLE 1 ). Live animals ( Fig. 1 View FIGURE 1 C) translucent, preserved opaque white. Pigmentation consisting only of few small irregular red spots on anterior part of body.

Prostomium anteriorly rounded, wider than long, dorsoventrally flattened, bearing pair of dorsal cylindrical antennae, palps absent, replaced by ciliated pads ( Fig. 5 View FIGURE 5 A–E). Anterior part of prostomium and tips of antennae with small bundles of adjoined tactile cilia, appearing spike-like in living animals. Ciliary bands separated by gaps; two bands of cilia encircling prostomium, one complete circle in front of antennae, and one incomplete circle at level of antennae. Latter interrupted by antennae; cilia between antennae slanting posteriorly, separated by small mid-dorsal space, giving appearance of eyebrows. Additional ventral semicircle of cilia anterior to complete circle. Posterior border of prostomium indicated dorsally by four nuchal organs, ventrally by mouth, lateral restrictions almost absent.

Peristomium represented by two apodous, achaetous segment-like rings, each surrounded by complete circle of cilia. Two eyes, slightly below border between prostomium and peristomium, between inner and outer nuchal organs. Eyes internal, visible only in living animals. Eyes with refractive crystalline platelets as typical for Ophryotrocha , appearing silvery white under incident light ( Fig. 1 View FIGURE 1 C). Following chaetigers with dorsal and ventral ciliary bands ( Fig. 5 View FIGURE 5 F), laterally interrupted by parapodia.

Parapodia uniramous, with acicular lobe and ventral retractile lobe supported by short simple chaeta; dorsal and ventral cirri absent. Supra-acicular fascicle consisting of 2–3 simple chaetae, subacicular fascicle with 2–3 heterogomph falcigers and inferiormost simple chaeta. Appendages of falcigers and upper part of simple chaetae serrated with simple distal tip. Mammillate rosette glands, two per segment, present dorsolaterally on up to 9 posterior segments. Pygidium bearing dorsal anus and pair of dorsal pygidial cirri; dorsal stylus absent ( Fig 5 View FIGURE 5 F).

Jaws consisting of mandibles and maxillae; former permanent, latter undergoing at least two moults. Mandibles consisting of two elongate shafts, widening distally into bifid serrated cutting plates with 20–24 tiny teeth and large blunt sublateral tooth-like projection at anterior cutting edge of each plate ( Fig 3 View FIGURE 3 G). Shafts of adult animals 125–140 µm long, with basal and distal lateral thickenings ( Fig. 3 View FIGURE 3 H). Maxillary apparatus of P-type only, consisting of forceps fused with carrier-like structure and seven pairs of anterior denticles (D) ( Fig. 6 View FIGURE 6 C). Forceps of adult worms 90–125 µm long, median edge of anterior part of forceps with large distal fang and 3–5 large teeth irregularly alternating with small teeth, distal fang much larger than other large teeth ( Fig. 3 View FIGURE 3 I); D1–D3 with distal fang and coarsely serrated median cutting edge; D4–D7 with finely serrated edge, associated with oval ventral plate.

Reproduction and Development. Ophryotrocha birgittae is hermaphroditic. The first and second chaetigers are sterile, the third and fourth are male, and the remaining ones are female. The chromosome number is 2n = 8. Newly laid eggs are ovoid, 200 x 160 µm. The egg case is firm and elastic, transparent, and of fusiform shape, closed at both ends. The larvae are released from the egg case at the 4-chaetiger stage. Larval maxillae ( Fig. 6 View FIGURE 6 A) are present in up to 6-chaetiger animals, juvenile (P1) maxillae ( Fig. 6 View FIGURE 6 B) are found in 7- to 11-chaetiger animals, and adult (P2) maxillae ( Fig. 6 View FIGURE 6 C) from 12-chaetiger animals onwards. Other reproductive and population parameters are listed in Table 2 View TABLE 2 and will be compared for the three species in the ‘Discussion” below.

Etymology. This species is named in honour of Birgitta Åkesson, in appreciation of her continuous support and understanding.

Remarks. The new species was originally identified through crossbreeding experiments and has been confirmed by gene sequence studies ( Dahlgren et al. 2001; Heggøy et al. 2007). It can be distinguished from the other two species of the O. diadema group by having separate reflective eyes, while in O. diadema the eyes are connected, and those of O. alborana have an additional red pigment cup ( Fig. 1 View FIGURE 1 ), as well as other subtle morphological differences ( Table 1 View TABLE 1 ), and differing life history parameters ( Table 2 View TABLE 2 ).

An egg colour polymorphism resulting from a recessive mutant causing the eggs to be white instead of yellow, described for O. diadema above, has also been observed in O. birgittae .

Ophryotrocha puerilis was reported from the littoral zone of Qingdao harbour by Wu (1981). Wu stated that it occurred in abundance and remained on muddy stones during low tides, suggesting that it might be identical with the species described here. However, the sketch accompanying Wu’s note shows the presence of palps which are found in O. puerilis but absent in O. birgittae .

Distribution. East China Sea, Yellow Sea: Qingdao.