Asterocheres corneliae Schirl 1973

Asterocheres corneliae Schirl, 1973

(Figs. 1–2)

Asterocheres corneliae Schirl, 1973: 71 –77; Figs. 3–4, 5 (g–j)

Material examined. Six females (NHMUK reg. no 1986.385), associated with a red sponge collected in a bay situated 2 km north of Banyuls-sur-Mer, France; August 1983.

Description of female. Body cyclopiform, with oval cephalothorax and cylindrical urosome (Fig. 1 A). Mean body length 756µm (n = 5; 710–790 µm) and mean maximum width 385 µm (n = 5; 375–404 µm). Prosome comprising cephalothorax (fully incorporating first pedigerous somite) and three free pedigerous somites.

Urosome 4-segmented, comprising leg 5-bearing somite, genital double-somite and two free abdominal somites (Fig. 1 B). Except for leg 5-bearing somite, all other urosomites ornamented with epicuticular scales. Genital double-somite (Fig. 1 B) slightly wider than long; paired genital apertures bipartite, each comprising lateroventral copulatory pore and dorsolateral gonopore (oviduct opening); lateral margins with long spinules in middle third (posterior to genital apertures). Each genital area provided with one very plumose seta (Fig. 1 B).

Caudal rami (Fig. 1 B) about as long as wide (measured along outer margin); armed with six setae: seta I absent; setae III–VI all plumose and arranged around posterior margin; insertion sited of setae II and VII slightly displaced onto dorsal surface, both of them smooth.

Antennule (Fig. 1 C) 21-segmented, about 375 µm long. Segmental fusion pattern and armature as follows: 1(I)-1, 2(II)-1, 3(III)-1, 4(IV)-2, 5(V)-2, 6(VI)-2, 7(VII)-1, 8(VIII)-2, 9(IX–XII)-8, 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–XXIV)-3, 20(XXV–XXVI)-3 and 21(XXVII–XXVIII)-6. Segment 10(XIII) reduced, forming incomplete sclerite partly overlapped by distal expansion of compound segment 9(IX–XII).

Antenna (Fig. 1 D) biramous, about 240 µm long including terminal claw. Coxa small and ornamented with tuft of spinules in distal inner margin. Basis elongate and unarmed. Exopod 1-segmented, about twice longer than wide, armed with one lateral seta, one short subterminal seta and one very long terminal seta, all of them smooth. Endopod 3-segmented; proximal segment elongate and ornamented with rows of spinules along inner margin; middle segment produced distally on medial side but articulating with distal segment proximally on lateral side, bearing one plumose distal seta which is longer than the entire segment; distal segment armed with two subterminal setae, one of them plumose, and apical claw.

Siphon reaching to between bases of maxillipeds and intercoxal sclerite of leg 1.

Mandible (Fig. 2 A) comprising stylet-like gnathobase and slender 1-segmented palp. Stylet with denticulate margin subapically. Palp elongated, with row of spinules at medial side and two barbed terminal setae of unequal length.

Maxillule (Fig. 2 B) bilobed; praecoxal gnathobase (inner lobe) 3.5 times longer than palp (outer lobe). Praecoxal endite ornamented with short spinules laterally and tuft of long spinules medially; armed with five terminal setae, one of them very short and naked. Palp bearing two subterminal setae (one of them barbed and very short and the other one long and plumose) and two plumose terminal setae, equal in length.

Maxilla (Fig. 2 C) 2-segmented. Coxa with row of spinules along proximal inner margin (not figured). Basis claw-like, longer than coxa, with recurved tip and ornamented with row of spinules in distal half.

Maxilliped (Fig. 2 D) 5-segmented, comprising short syncoxa, long basis and 3-segmented endopod. Syncoxa with one short smooth seta along distal inner margin. Basis elongate with few short spinules along outer margin and minute seta halfway along inner margin. First endopodal segment compound, partial suture marking original separation of two ancestral segments, armature formula (2,0); second endopodal segment short, bearing one short naked seta medially; third endopodal segment armed with terminal claw plus additional plumose subterminal seta. Distal two-thirds of claw provided with spinules along medial margin.

Swimming legs 1–4 (Fig. 4 A–D) biramous, with 3-segmented rami and intercoxal sclerite present in all legs (legs 1–4 as described and illustrated by Schirl (1973)). Spine and seta formula:

Fifth leg (Fig. 1 B) with protopod incorporated into somite; outer basal plumose seta displaced to laterodorsal surface, longer than entire free segment. Exopod elongate, with three terminal setae, the longest two smooth and stout and the short one densely plumose; outer and inner margins with spinules.

Sixth leg (Fig. 1 B) represented by paired opercular plates closing off gonopores on genital double-somite; armed each with one very plumose seta.

Male. Not examined.

Discussion. Schirl’s (1973) description was based on specimens collected from Banyuls in the early 1960s that were found to be associated with three species of calcarean sponges, i.e. Clathrina clathrus (Schmidt, 1864), C. primordialis (Haeckel, 1872) and Ascandra contorta (Bowerbank, 1866). The specimens deposited in the Natural History Museum of London are labelled Asterocheres cf. corneliae, and upon re-examination were confirmed to belong to this species. However, some discrepancies with the original description were observed, including: (1) the antennule is 20-segmented in the female in the original description, although the illustration shows a 20-segmented antennule with the last segment indistinctly 2-segmented (with three and three setae each); our re-examination showed that the antennule is 21-segmented, with the last two segments clearly divided (three and six setae each); (2) the antenna bears three setae on the exopod instead of the two setae illustrated by Schirl, and the proximal segment of the endopod is ornamented with rows of spinules along the inner margin; (3) the mandibular palp was described as “probably 2-segmented, but the dividing line is barely visible”; the mandibular palp proved to be clearly 1-segmented and the stylet of the mandible is illustrated here for the first time; (4) the outer lobe of the maxillule is smaller and the terminal setae are shorter than those shown in the original description; the inner lobe is provided with one additional seta; (5) row of spinules along proximal inner margin in the coxa and row of spinules in distal half of basis claw-like are missing in Schirl’s illustration of the maxilla; (6) the minute seta halfway along inner margin of basis and one seta on first endopodal segment are missing in Schirl’s description of the maxilliped; (7) the leg 5-bearing somite and all other urosomites are ornamented with epicuticular scales which were overlooked in the original illustration.

Despite the discrepancies observed between the specimens examined herein and the original description, the species is easily identifiable as A. corneliae. As in other redescriptions of Asterocheres species (Bandera & Conradi 2009a, 2009b, 2013, 2014; Kim 2010), such discrepancies are mainly confined to the ornamentation and armature of oral appendages and are relatively common in descriptions published 40 or more years ago.

Asterocheres corneliae belongs to the group of Asterocheres species that display a 21-segmented antennule in the female. This group includes 27 species: A. astroidicola Conradi, Bandera & López-González, 2006, A. echinicola (Norman, 1868), A. ellisi Hamond, 1968, A. eugenioi Bandera & Conradi, 2014, A. faroensis Crescenti, Baviera & Zaccone, 2010, A. flustrae Ivanenko & Smurov, 1997, A. genodon Stock, 1966, A. hirsutus Bandera, Conradi & López-González, 2005, A. hoi Bandera & Conradi, 2013, A. jeanyeatmanae Yeatman, 1970, A. kervillei Canu, 1898, A. latus (Brady, 1872), A. lilljeborgii Boeck, 1860, A. madeirensis Bandera, Conradi & López- González, 2007, A. minutus (Claus, 1889), A. nudicoxus Kim, 2010, A. peniculatus Kim, 2010, A. reginae Boxshall & Huys, 1994, A. sarsi Bandera & Conradi, 2009b, A. simulans (Scott, 1898), A. siphonatus Giesbrecht, 1897, A. suberitis Giesbrecht, 1897, A. tarifensis Conradi & Bandera, 2011, A. tenerus (Hansen, 1923), A. tenuicornis Brady, 1910, A. tubiporae Kim, 2004b, and A. urabensis Kim, 2004a.

Only six species of the group listed above are reported to have a 1-segmented mandibular palp as in A. corneliae, i.e. A. echinicola, A. faroensis, A. madeirensis, A. minutus, A. nudicoxus and A. siphonatus. The remaining species exhibit a 2-segmented mandibular palp. Although A. nudicoxus was described by Kim (2010) as having a 1-segmented mandibular palp, in the description he pointed out that the palp showed a vestigial articulation which was displayed in the illustration (Kim 2010: Fig. 34A). This vestigial articulation and the characteristic shape of the genital double-somite, consisting of a broad anterior part and a very short, narrower posterior part, with the anterior part strongly tapering anteriorly (Kim 2 010: Fig. 33B) serve to separate A. nudicoxus from A. corneliae.

Two species, A. echinicola and A. minutus, differ from A. corneliae by the morphology of the maxillule. In both species the inner and outer lobes are approximately equal in length, and one of the four terminal setae on the inner lobe is four times longer than the remaining three setae (Bandera & Conradi 2009b; Conradi & Bandera 2011). In contrast, A. corneliae has an inner lobe which is about 3.5 times longer than the outer and bears four long and one short distal setae.

Asterocheres siphonatus can easily be separated from A. corneliae by the length of the siphon. In A. corneliae it extends beyond the bases of the maxillipeds but does not reach the intercoxal sclerite of the first leg, whereas in A. siphonatus the siphon extends to the posterior margin of the intercoxal sclerite of the fourth leg (Conradi & Bandera 2011).

Detailed comparison between A. corneliae and A. faroensis reveals a number of significant differences, including the size of the caudal rami (about as long as wide in A. corneliae compared to 1.7 times longer than wide in A. faroensis) and the more dorso-ventrally flattened prosome in A. faroensis (Crescenti et al. 2010). The long aesthetasc-like element on the coxal part of maxilla is present in A. faroensis but was not discernible in A. corneliae.

The most similar species of the group mentioned above is A. madeirensis which can be distinguished by the following differences: (1) antennary exopod armed with two setae in A. madeirensis and three setae in A. corneliae; (2) mandibular stylet pointed in A. madeirensis but denticulated in A. corneliae; (3) siphon slightly longer in A. corneliae; (4) inner lobe of maxillule three times longer than outer lobe in A. madeirensis but four times longer in A. corneliae; (5) aesthetasc-like element present on coxal part of maxilla in A. madeirensis but absent in A. corneliae; (6) outer basal seta of protopod of leg 5 longer than the entire free segment in A. corneliae but shorter in A. madeirensis; and (7) lateral margins of the genital double-somite with long spinules in the middle third in A. corneliae, but much more spinous in A. madeirensis (Bandera et al. 2007).