Asterocheres boeckii ( Brady, 1880 )

Bandera, Eugenia & Conradi, Mercedes, 2016, Redescription of two species of Asterocheres Boeck, 1860 (Copepoda: Siphonostomatoida), A. corneliae Schirl, 1973 and A. boeckii (Brady, 1880), and proposal of a new genus for Asterocheres fastigatus Kim, 2010, Zootaxa 4174 (1), pp. 259-273 : 264-269

publication ID	https://doi.org/ 10.11646/zootaxa.4174.1.18
publication LSID	lsid:zoobank.org:pub:079EBF5C-62E3-4DF4-AF30-983A7647096C
DOI	https://doi.org/10.5281/zenodo.6090120
persistent identifier	https://treatment.plazi.org/id/BC704947-FF90-7630-FF6A-9DCA7F21FD20
treatment provided by	Plazi
scientific name	Asterocheres boeckii ( Brady, 1880 )
status

Treatment

Asterocheres boeckii ( Brady, 1880)

( Figs. 3–5 View FIGURE 3 View FIGURE 4 View FIGURE 5 )

Artotrogus Boeckii Brady, 1880: 60 –61; Plate XCI, figs. 1–9.

Material examined. (a) seven females ( ZMO F21599) from Ranø, collected by G.O. Sars; (b) two females ( ZMUC; CRU- 4936 ) from Talsnafiord Island , 1893; (c) three females (NHMUK-1911.11.8.47282–286) from Salcombe, Devon, England, 1875 (Norman collection); (d) seven females, three juveniles (NHMUK-1986.381) from Loch Riddon (Loch Ruel), Argyll and Bute, Scotland .

Description of female. Body cyclopiform, with very broad prosome and cylindrical urosome ( Fig. 3 View FIGURE 3 A). Mean body length 864µm (n = 4; 791–920 µm) and mean maximum width 497 µm (n = 4; 396–620 µm). Prosome comprising cephalothorax (fully incorporating first pedigerous somite) and three free pedigerous somites. Cephalothorax with posterolateral angles rounded. Somites bearing legs 2–3 very broad; epimeral areas with posterolateral angles rounded. Somite bearing leg 4 much smaller and narrower than preceding ones, largely concealed under pleurotergite of leg 3-bearing somite.

Urosome 4-segmented, comprising leg 5-bearing somite, genital double-somite and two free abdominal somites. Posterior hyaline frills of urosomites with serrate free margins ( Fig. 3 View FIGURE 3 B). Genital double-somite ornamented with flattened epicuticular scales arranged in irregular pattern dorsally ( Fig. 3 View FIGURE 3 B); about as long as wide; paired genital apertures bipartite, each comprising lateroventral copulatory pore and dorsolateral gonopore (oviduct opening); lateral margins with setular tufts in distal half (posterior to genital apertures).

Caudal rami ( Fig. 3 View FIGURE 3 B) slightly wider than long (measured along outer margin); trapezoid with inner margin shorter than outer one; armed with six setae; seta I absent; setae II–VII all arranged around posterior margin with setae II and VII slightly displaced onto dorsal surface.

Antennule ( Fig. 3 View FIGURE 3 D) 21-segmented, about 370 µm long. Segmental fusion pattern and armature as follows: 1(I)-2, 2(II)-2, 3(III)-2, 4(IV)-2, 5(V)-2, 6(VI)-1, 7(VII)-1, 8(VIII)-2, 9(IX–XII)-7, 10(XIII)-1, 11(XIV)-1 + 1 spine, 12(XV)-2, 13(XVI)-2, 14(XVII)-2, 15(XVIII)-2, 16(XIX)-2, 17(XX)-2, 18(XXI)-2 + 1 aesthetasc, 19(XXII–XXIII)-2, 20(XXIV–XXV)-3 and 21(XXVI–XXVIII)-6. Segment 10(XIII) reduced, forming incomplete sclerite partly overlapped by distal expansion of compound segment 9(IX–XII).

Antenna ( Fig. 3 View FIGURE 3 E) biramous, about 350 µm long including terminal claw. Coxa unarmed, with few spinules. Basis unarmed, with fine spinule row as shown in Figure 3 View FIGURE 3 E. Exopod 1-segmented, small, about 1.5 times longer than wide; with one short proximal seta and two terminal setae unequal in length, all of them smooth. Endopod 3- segmented; proximal segment elongate, ornamented with lateral and distal rows of fine spinules; middle segment produced distally on medial side but articulating with distal segment proximally on lateral side, bearing one distal smooth seta; distal segment with long terminal claw and two subterminal pinnate setae; inner margin of distal segment and claw with spinules.

Siphon reaching to the intercoxal sclerite of leg 1.

Mandible ( Fig. 4 View FIGURE 4 B) comprising stylet-like gnathobase and slender 2-segmented palp. Proximal segment of palp longest (3.9 times longer than distal one), ornamented with rows of spinules; short distal segment, with two plumose unequal apical setae.

Stylet located in oral cone, with denticulate margin subapically as figured.

Coxae ornamented with spinule rows around outer margin; inner coxal seta short and naked in legs 1 and 4, long and plumose in legs 2–3. Outer basal seta long and naked in legs 1–2 and short in legs 3–4 (the last one plumose). Outer spines of exopodal segments in legs 1–4 bilaterally serrate. Lateral margin of exopodal segments with minute serrations or spinular rows; those of endopodal segments with rows of setules.

Maxillule ( Fig. 4 View FIGURE 4 A) bilobed. Inner lobe much larger than outer lobe, about three times longer than wide. Inner lobe ornamented with spinules on lateral margin and tuft of long setules medially; armed with one minute and naked seta and four long but unequal setae, latter setae ornamented with spinules. Outer lobe armed with two long plumose setae, one subterminal spinulose seta and one lateral stout seta densely covered by spinules ( Fig. 4 View FIGURE 4 A).

Maxilla ( Fig. 3 View FIGURE 3 F) 2-segmented but with partial transverse surface suture on syncoxa (proximal segment) possibly marking plane of praecoxa-coxa fusion; praecoxal portion bearing flaccid aesthetasc-like element medially, representing tubular extension of external opening of maxillary gland; coxal portion unarmed. Basis claw-like and much longer than coxa, more or less straight but recurved towards the apex; margins provided with rows of spinules as figured.

Maxilliped ( Fig. 4 View FIGURE 4 C) 5-segmented, comprising short syncoxa, long basis and 3-segmented endopod. Syncoxa with one short seta distally. Basis with few spinules on distal outer margin. First endopodal segment bearing two unequal distal setae; second endopodal segment with one plumose medial seta; third endopodal segment bearing recurved terminal claw and subterminal plumose seta. Distal margin of claw with rows of spinules.

Swimming legs 1–4 ( Fig. 5 View FIGURE 5 A–D) biramous, with 3-segmented rami; intercoxal sclerite present. Spine and seta formula as follows:

Fifth leg ( Fig. 3 View FIGURE 3 B–C) with protopod incorporated into somite; outer basal seta displaced to laterodorsal surface. Free segment elongate-oval, with three terminal setae, two of them long and pinnate and one of them shorter and plumose; margins with spinules.

Sixth leg ( Fig. 3 View FIGURE 3 B) represented by paired opercular plates closing off gonopores on genital double-somite; armed each with one plumose seta and one spiniform element.

Discussion. This species was originally described by Brady (1880) under the name Artotrogus boeckii Brady, 1880 , based on two or three specimens taken in a surface-net, and amongst weeds, at about 3.6 m depth in Westport Bay (Co. Mayo) and Roundstone Bay (Co. Galway), on the west coast of Ireland. Most workers have subsequently referred to it as Asterocheres boecki (e.g. Sars 1915; Stock 1966; Hamond 1973; Schirl 1973; Humes 1980; Kim 2014). However , the use of the genitive ending -i in a subsequent spelling of a species-group name that is a genitive based upon a personal name in which the correct original spelling ends with -ii, is to be treated as an incorrect subsequent spelling, even if the change in spelling is deliberate ( ICZN Art. 33.4). The correct spelling of the specific epithet should therefore be boeckii and is reinstated here. The same applies to the type species of the genus which is widely cited as Asterocheres lilljeborgi but was originally spelled as A. Liljeborgii by Boeck (1860). Since the species was named after the Swedish zoologist Wilhelm Lilljeborg, the incorrect original spelling was subsequently corrected to lilljeborgi by Brady (1880), Canu (1892), Giesbrecht (1997) and others, but unfortunately, the correct suffix –ii was lost in the process. The correct spelling is adopted here as Asterocheres lilljeborgii Boeck, 1860 . Similarly, the type species of Ascomyzon Thorell, 1859 (a synonym of Asterocheres ), should be cited by its original spelling Ascomyzon lilljeborgii Thorell, 1859 . Note that Ascomyzon (published 14 Sep 1859) takes priority over Asterocheres Boeck, 1860 (date of publication to be adopted is 31 December when only the year is specified or demonstrated ( ICZN 21.3.2)). A ruling by the International Commission on Zoological Nomenclature will be required to avoid upsetting a long-accepted name in its accustomed meaning. In addition, since Ascomyzon lilljeborgii Thorell, 1859 has become the senior secondary homonym of Asterocheres lilljeborgii Boeck, 1860 , the latter will need to be replaced, in this case by its oldest junior synonym, Asterocheres asterocheres ( Sars, 1915) .

Brady (1880) listed Ascomyzon lilljeborgii Thorell, 1859 as a synonym of A. boeckii , although in the text he mentioned that Thorell’s (1859) specimens were obtained from Corella (as Ascidia ) parallelogramma ( Müller, 1776) and he himself “… had never seen any examples taken from ascidians”. Giesbrecht (1899), in his monograph of asterocherids from the Gulf of Naples, amended the description of A. boeckii and illustrated the male and female. However, Sars (1915) pointed out that the specimens used in Giesbrecht’s redescription of A. boeckii belonged to another species which was later described by Stock (1960) as Asterocheres complexus Stock, 1960 . In the same paper, Sars also redescribed A. boeckii , transferred it to Ascomyzon ( Asterocheres was considered invalid), and stated that Asc. lilljeborgii Thorell, 1859 and Asc. lilljeborgii ( Boeck, 1860) were different species, both being distinct from Asc. boeckii ( Brady, 1880) .

Asterocheres boeckii was poorly described and illustrated by Brady (1880) and the only available redescription and illustrations that are more complete are those by Sars (1915). The specimens of this species deposited in different European museums show some discrepancies with the previous descriptions, i.e. (1) the antennule is 21- segmented in female instead of the 20 segments reported by Brady and Sars; (2) the antennary exopod has not two but three elements; Sars missed one lateral seta; (3) although Brady described the mandible in the text as “… produced into a long filiform seta, and destitute of a palp”, his illustration shows a 1-segmented palp with two terminal setae ( Brady 1880: Plate XCI, Fig. 3 View FIGURE 3 ); the stylet is here described and illustrated for the first time; (4) the inner lobe of the maxillule possesses five setae instead of the four setae illustrated by Sars; (5) the maxilla has a long aesthetasc-like element medially which was not illustrated or mentioned in previous descriptions; (6) the maxilliped is 5-segmented with the armature formula: (1, 0, 2, 1, 1 + claw), but the majority of these setae or spines are missing in preceding descriptions; (7) according to Sars’s illustration, the armature formula for the second endopodal segment of leg 4 is (0-1); however, the second endopodal segment of leg 4 bears two setae as is usual for the genus; and (8) the exopod of leg 5 shows not two but three terminal setae; there is one terminal seta missing in previous descriptions.

This species belongs to the Asterocheres species group characterized by 21-segmented antennules in the females, a 2-segmented mandibular palp and a siphon reaching to the intercoxal sclerite of leg 1. This group is composed of nine species: A. ellisi , A. eugenioi , A. hirsutus , A. hoi , A. latus , A. peniculatus , A. sarsi , A. tenuicornis and A. urabensis . Although there is no information about the length of the siphon in A. tenuicornis , this species can easily be separated from A. boeckii by the length of the caudal rami, being six times longer than wide, the longest within the genus ( Eiselt 1965). Caudal ramus length can also be used to separate both A. latus and A. hirsutus from A. boeckii since the caudal rami is 2.6 times longer than wide in A. latus , 2.5 times longer than wide in A. hirsutus and slightly wider than long in A. boeckii ( Bandera & Conradi 2009b; Bandera et al. 2005).

Asterocheres boeckii can be separated from A. ellisi , A. eugenioi and A. sarsi by differences in body shape. While A. boeckii shows a cyclopiform body, with very broad prosome and cylindrical urosome, A. ellisi is characterized by a dorsoventrally flattened prosome ( Hamond 1968: Fig. 7); A. eugenioi and A. sarsi have an oval cephalothorax, a cylindrical urosome, and epimeral areas of somites bearing legs 2–3 with pointed posterolateral angles ( Bandera & Conradi 2014: Figs. 2 View FIGURE 2 A, 6A).

Kim (2010) stated that “… A. boeckii differs from A. peniculatus having the more expanded prosome, the narrower genital double-somite which is as long as wide, the rostrum with rounded posterior margin, a single inner seta on the second endopodal segment of leg 4, and only two distal setae on the free segment of leg 5, according to the description and figures made by Sars (1915) ”. After our redescription of A. boeckii , it is now confirmed that the last two differences do not exist and A. peniculatus and A. boeckii share a similar leg 4 and exopod of leg 5. However the other three differences listed above remain valid to separate these two species.

Two other species are very similar to A. peniculatus and A. boeckii , i.e. A. genodon and A. astroidicola . The latter can be distinguished from the first two by the length of the siphon (extending beyond the intercoxal sclerite of leg 2 in A. astroidicola but reaching the bases of leg 1 in A. peniculatus and A. boeckii ) ( Conradi et al. 2006). Furthermore, A. genodon shows a feature that separates this species from the other three: the presence of seven caudal setae, including a small, naked ventral seta ( Kim 2010: Fig. 39C).

The remaining two species of the group, A. hoi and A. urabensis , differ from A. boeckii in the morphology of the free segment of leg 5, the maxillule and the terminal spine of the third exopodal segment of legs 2–4. The exopod of leg 5 is 2.5 times longer than wide in A. hoi , 3.8 times longer than wide in A. urabensis but only 1.9 times longer than wide in A. boeckii . The length ratio between the inner and outer lobes of the maxillule is about 3 in A. hoi and A. urabensis , but only 1.8 in A. boeckii . The terminal spine of the third exopodal segment of leg 2–4 is much longer than the entire segment in A. boeckii ; in contrast, this spine is almost equal in length or slightly shorter than the segment in A. hoi and A. urabensis ( Kim 2004a; Bandera & Conradi 2013).