Krohnia cf. lepidota ( Krohn, 1845 )

Krohnia cf. lepidota ( Krohn, 1845) View in CoL

( Figs 1–4 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 )

Alciopa lepidota Krohn, 1845: 171 View in CoL , 175, Pl. 6 Figs 10–13 View FIGURE 10 View FIGURE 11 View FIGURE 12 View FIGURE 13 [original description; Sicily, Italy]

Mediterranean records.

Alciopa lepidota Hering 1892: 757–760 View in CoL , Pl. VI, Figs 4–9 View FIGURE 4 View FIGURE 5 View FIGURE 6 View FIGURE 7 View FIGURE 8 View FIGURE 9 [description; Sicily]

Krohnia lepidota Quatrefages 1865b View in CoL , 158–159 [brief description; Sicily]

Callizonella lepidota Fauvel 1923: 211–212 View in CoL , Fig. 79 e–h [description; France].— Wesenberg-Lund 1939: 38 [description; widely in Mediterranean]

Atlantic records.

Alciopa lepidota Langerhans 1880: 312 View in CoL [brief description; Madeira]

Krohnia lepidota Støp-Bowitz 1948: 33 View in CoL [description; west of Canary Islands and central Atlantic], 1992: 58–60 [description; off Central Africa].— Day 1967: 178–179, Fig. 7.1 I–K View FIGURE 7 [description; off South Africa].— Tebble 1960: 193, 255–256, Fig. 50 (map of records) [description, biogeography; sub-tropical and tropical Atlantic].— Rice 1987: 120–122, Figs 1 B View FIGURE 1 , 3 D View FIGURE 3 , 4 C View FIGURE 4 , 5 F View FIGURE 5 [detailed comparison with Krohnia foliocirrata Rice, 1984; Bahama Islands]

Callizona cincinnata Greeff, 1876: 71–72 View in CoL , Pl. 5 Figs 56–59 [original description; Canary Islands]

Alciopa cirrata Greeff, 1876: 60–62 View in CoL , Pl. 1, Figs 5–6 View FIGURE 5 View FIGURE 6 and pl. 2 Figs 19–21 [original description; Canary Islands]

Callizonella lepidota Apstein 1900: 12–13 View in CoL , Pl. 2 Figs 11–13 View FIGURE 11 View FIGURE 12 View FIGURE 13 [description; equatorial to subtropical Atlantic].— Fauvel 1923: 211–212, Fig. 79 e–h [description; France]

Pacific records.

Krohnia lepidota Ushakov 1972: 207–208 View in CoL , Pl. XXVI Figs 1–4 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 [description; northwest Pacific].— Fernández-Álamo 1983: 89– 93, Fig. 22 [description; off Mexico and Central America] — Rozbaczylo et al. 2020: 153–154, Fig. 5 E–F View FIGURE 5 [description; northwest of Juan Fernandez archipelago, Chile]

Callizonella pigmenta Treadwell, 1943: 38 View in CoL , Pl. II Fig. 25 [original description; off Central America]

Indian Ocean records.

Krohnia lepidota Day 1967: 178–179 View in CoL , Fig. 7.1 I–K View FIGURE 7 [description; Agulhas Current, Mocambique Current]

Material examined. One specimen: ZMMU WS20944 View Materials (FA, Et) .

Description. Moderately preserved anterior part with 11chaetigers, 2.5 mm long, 0.7 mm wide at 10 th chaetiger. Body slender, fragile. Prostomium small, not extending in front of eyes. Frontal antennae subequal, large and tapering, inserted close to each other ( Fig. 2 View FIGURE 2 ). Their ventral surface with a few longitudinal rows of small papillae (ventro-lateral rows may be seen from above). Median antenna of about same length, fusiform, its base sandwiched dorsally between eyes ( Fig. 2A View FIGURE 2 ). Proboscis not everted in our specimen. Eyes large and directed obliquely forward and upwards ( Fig. 2A View FIGURE 2 ). Tentacular cirri arranged as ( Fig. 2B View FIGURE 2 ). Dorsal cirri of second pair (D2) shorter than D1 and D3 (D3>D1>D2). D1 stout, extending considerably beyond outer margin of the eyes. D3 enlarged; cirrophores extend laterally as wide as eyes’ outer margins. Cirrostyles long, cylindrical, with longitudinal row of large papillae ventrally. Total length of each cirrus exceeds distance between eyes’ outer margins. Ventral cirri smaller than corresponding dorsal ones; V2 tapering, V3 foliaceous, can be mistaken for ventral parapodial cirri in dorsal view. All parapodia well-developed ( Fig. 3 View FIGURE 3 ). Dorsal parapodial cirri lost in our specimen; their cirrophores swollen. Chaetigerous lobes with short cirriform appendage and protruding aciculum. Ventral cirri 1.5–2 times shorter than parapodial lobes, asymmetrically lanceolate, slightly swollen. Chaetae all simple. First pair of parapodia with one or two stout acicular chaetae ( Fig. 3A View FIGURE 3 ). They are straight with the very tip distinctly curved. Next 4 parapodia with 2–5 stout acicular chaetae with smoothly curved tips located ventral to aciculum ( Fig. 3B View FIGURE 3 ). Two straight acicular chaetae per parapodium in succeeding 4–5 chaetigers ( Fig. 3C View FIGURE 3 ); single straight and long acicular chaeta per parapodium in rest of segments ( Fig. 3D View FIGURE 3 ). Capillaries present in all parapodia. In first pair, one or two chaetae of transitional type present (either short stout capillaries, or slender acicular chaetae). Several short regular capillaries present from second pair of parapodia. Posteriorly, capillaries form broad fan; their size and number increase backwards ( Fig. 3B–D View FIGURE 3 ). Segmental glands are vertical cushions located laterally posterior to parapodia from segment 9 (sixth parapodium) ( Figs 2 View FIGURE 2 , 3C–D View FIGURE 3 ). Margins of ventral parapodial cirri, antennae and tentacular cirri are highly glandular (seen as granular areas which are densely stained by methyl green).

Coloration: anterior part transparent with brownish pigmentation confined to parapodial bases, boundaries of segments and mid-ventral line. From first segment with glands, coloration becomes darker, especially around glands. Segmental glands dark brown (almost black). Characteristic pattern is formed by brown dots. Dorsum ( Fig. 2A View FIGURE 2 ): two longitudinal rows formed by one or two dots at each parapodial base. Ventrum ( Fig. 2B View FIGURE 2 ): two lateral rows formed by dots at parapodial bases (posteriorly obscured by segmental glands. Three (rarely four) dots per segment form ventral middle row. Areas of midline containing dots are slightly swollen. One to three faint (reddish) brown dots along margins of ventral parapodial cirri ( Fig. 3 View FIGURE 3 ).

Remarks. Many authors described Krohnia lepidota from different localities; however, their descriptions do not quite match and/or leave some important features uncertain. These differences cannot be readily attributed to geographically distinct populations because contradicting statements are sometimes obtained from the same area. The main features used to distinguish between species of Krohnia are the size of dorsal parapodial cirri, the number of acicular chaetae in anterior chaetigers and the size of the tentacular cirri pair D3. Of these, only strongly enlarged tentacular cirri D3 are consistent throughout the descriptions of the species. Along with the characteristic pattern of black/brown dots they were used as the basis for synonymization of some Alciopa , Callizona and Callizonella species with Krohnia lepidota ( Apstein 1900; Støp-Bowitz 1948; Dales 1957; Dales & Peter 1972). These notably enlarged tentacular cirri D3 are found in our specimen, as well. However, a unique feature of its tentacular arrangement is that the smallest pair of dorsal tentacular cirri is D2, whereas in all available descriptions the size of dorsal cirri simply increases from D1 to D3.

The presence of acicular chaetae in the anterior segments is not specified in the first description by Krohn (1845); just their presence is noted in descriptions of Callizona cincinnata and Alciopa cirrata by Greeff (1876). Apstein (1900) who studied Krohn’s and Greef’s specimens along with his own material mentions a “big number” of acicular chaetae in anterior segments. The same is described by Fernández-Álamo (1983), Ushakov (1972) states that they “predominate”. On the contrary, their number is defined as “some” by Støp-Bowitz (1948), “few” ( Day, 1967) or “several” ( Rozbaczylo et al., 2020), all agreeing in that posteriorly their number reduces to 1 or they disappear. Rice (1987), who regarded the number of acicular chaetae per parapodium in anterior segments as one of the important features was the first to provide certain values: 1–3 per parapodium; the same is given in ( Støp-Bowitz 1992). A curious case is Callizonella pigmenta which was described as having more numerous acicular chaetae (“crotchets”) in parapodia of its rear rather than anterior part ( Treadwell 1943). However, Dales (1957) examined Treadwell’s type specimen and came to a conclusion that it is with no doubt conspecific with K. lepidota . Unfortunately, he did not comment on its acicular chaetae arrangement. In our specimen, 2–5 acicular chaetae are found in anteriormost chaetigers which is in line with more moderate estimates by Rice (1987) or Day (1967).

Length of dorsal parapodial cirri is described as equal to, or even shorter than parapodial lobe in Rice (1987). On the contrary, dorsal parapodial cirri exceeding parapodial lobe (2–3 times in anterior region and about 1.5 times posteriorly) are shown by Day (1967: Fig. 7.1 View FIGURE 7 , j–k), Ushakov (1972: pl. XXVI, 3) and Rozbaczylo et al. (2020: Fig. 5 View FIGURE 5 , E–F). However, some authors draw attention to the fact that dorsal cirri are easily lost and so cannot be described ( Støp-Bowitz, 1948; Fernández-Álamo, 1983). This is also true for our specimen.

The first description ( Krohn 1845) states that frontal antennae are attached close to each other. Frontal antennae arising “close together” from small prostomium which does not extend beyond eyes are also described by Day (1967) and can be seen from pictures by Ushakov (1972) and Fernández-Álamo (1983), although this is not specifically mentioned in descriptions. On the contrary, Greeff (1876) describes frontal antennae in Callizona cincinnata as located at both sides of anterior lobe of prostomium extending forward. Rozbaczylo et al. (2020) state that frontal antennae are located closely, but their picture clearly shows antennae attached at a distance from each other to a bluntly conical anterior portion of prostomium extending in front of eyes. Our Red Sea specimen agrees with the first description in having frontal antennae attached close to each other to a small anterior portion of prostomium.

Direction of eyes’ axes is described as obliquely forward and upward ( Støp-Bowitz 1948), slightly forward ( Day 1967; Rozbaczylo et al. 2020), sideways and slightly down ( Ushakov 1972), forward ( Fernández-Álamo 1983). In the Red Sea specimen, eyes’ axes are directed obliquely forward and upward in accordance with the description by Støp-Bowitz (1948).

Thus, compared to any of the cited description, some features of our specimen agree and some do not; but the same happens when comparing different descriptions to each other. The only unique feature of the Red Sea specimen is the arrangement of its tentacular cirri. However, without understanding true intra- and interspecific variability in Krohnia , size ratio of tentacular cirri alone is not enough to justify a new species without support from molecular data, especially with only one specimen at hand. Unfortunately, no sequences from K. lepidota s. l. (or any other species of the genus) are available so far. Thus, we regard K. lepidota as a species complex, until a study including material from different locations and involving molecular methods is carried out.

Distribution. The type locality of K. lepidota s. l. is Sicily, the Mediterranean. Later records include: equatorial to temperate Atlantic and Pacific; southwest Indian Ocean; central Red Sea (this study).