Asterocheres suberitis Giesbrecht, 1897

Bandera, Eugenia & Conradi, Mercedes, 2009, Redescription of Asterocheres suberitis Giesbrecht, 1897 and A. tenerus (Hansen, 1923) (Copepoda: Siphonostomatoida), including notes on A. abyssi (Hansen, 1923) and A. intermedius (Hansen, 1923), Zootaxa 1980, pp. 41-52 : 43-46

Asterocheres suberitis Giesbrecht, 1897

( Fig. 1 )

Cyclopicera echinicola (nec Norman, 1868): Giesbrecht 1895: 175.

Asterocheres suberitis Giesbrecht 1897: 254 ; Giesbrecht 1899: 70.

Asterocheres echinicola (nec Norman, 1868): T. Scott 1898: 270; T. Scott 1900: 389; Norman & T. Scott 1906: 192. Asterocheres suberitis antarctica T. Scott 1903: 573 .

Material examined. 7 Ψ and 4 ɗ ( ZMUC. CRU-8298) cotypes, ex Suberites domuncula (Olivi) , Gulf of Naples, leg. W. Giesbrecht in 1895.

Redescription of adult female: Body (see Giesbrecht 1899: fig. 1, Taf. 2) cyclopiform, with oval prosome and cylindrical urosome. Total length 840 µm (n = 1); maximum width 420 µm. Ratio of length to width of prosome 1.1:1. Ratio of length of prosome to urosome 1.6:1. Prosome comprising cephalothorax fully incorporating first pedigerous somite and 3 free pedigerous somites. Pedigerous somite 4 much smaller and narrower than preceding somites. Dorsal cephalothoracic shield and free pedigerous somites ornamented with integumental pores and sensillae. Urosome 4-segmented, comprising pedigerous somite 5, genital double-somite and 2 free abdominal somites. Genital double-somite about as long as wide; genital apertures separate, each comprising ventrolateral copulatory pore and dorsolateral gonopore (oviduct opening). Lateral margin of genital double-somite ornamented with setular rows posterior to genital apertures. Each genital area armed with seta. Caudal rami (see Giesbrecht 1899: fig. 7, Taf. 2) slightly more than 1.5 times longer than wide, armed with 6 setae (seta I absent); setae II–VII arranged along posterior margin.

Antennule (see Giesbrecht 1899: fig. 2, Taf. 2) 21-segmented, 360 µm long, with an aesthetasc on segment 18. Antenna ( Fig. 1 A) biramous, 234 µm long (including claw); coxa and basis unarmed. Exopod 1-segmented, slightly longer than wide, with small medial seta and 2 unequal terminal setae. Endopod 3- segmented; first segment elongated, ornamented with lateral row of fine spinules; second segment asymmetric, distomedially produced, and armed with simple seta; third segment with distal naked claw and two unequal, pinnate setae.

Siphon (see Giesbrecht 1899: fig. 13, Taf. 2) pyriform, about 130 µm long, reaching maxilliped insertions. Mandible ( Fig. 1 B) comprising stylet-like gnathobase and slender 2-segmented palp. Stylet with denticulate margin subapically. First segment of palp ornamented with lateral row of spinules; second segment ornamented with spinules apically and armed with 2 spinulate setae. Maxillule ( Fig. 1 C) bilobed. Praecoxal endite (inner lobe) 2.5 times longer than palp (outer lobe), ornamented with small spinules proximally and long setules apically, and armed with 4 distal setae (1 smooth, 2 spinulate, and 1 with apical spinules and spoonshaped tip). Palp armed with 4 pinnate setae. Maxilla (see Giesbrecht 1899: fig. 14, Taf. 2) 2-segmented, with curved claw-like basis. Maxilliped (see Giesbrecht 1899: fig. 16, Taf. 2) 5-segmented.

Swimming legs 1 and 4 as in original description (see Giesbrecht 1899: figs. 4 and 6, Taf 2). Legs 2 and 3 ( Figs 1 D–E) biramous and trimerous, with armature formula as follows:

Legs 2 and 3 outer exopodal spines bilaterally serrated. Intercoxal sclerites present in both legs. Leg 3 coxa ornamented with spinules along lateral margin ( Fig. 1 E).

Fifth leg (see Giesbrecht 1899: fig. 11, Taf. 2) 2-segmented, with protopod incorporated into somite; free segment oval, armed with 3 distal plumose setae, and ornamented with spinules. Sixth leg (see Giesbrecht 1899: fig. 7, Taf. 2) represented by paired opercular plates, each armed with seta, closing off gonopores on genital double-somite.

Adult male: Body (see Giesbrecht 1899: fig. 10, Taf. 2) cyclopiform, more slender than female, with oval cephalothorax and cyclindrical urosome. Total length 590 µm and maximum width 260 µm (n = 1). Prosome comprising cephalothorax fully incorporating first pedigerous somite and 3 free pedigerous somites. Urosome 5-segmented, comprising pedigerous somite 5, genital somite and 3 free abdominal somites. Caudal ramus as in female.

Appendages similar to those of female except for the following. Antennule (see Giesbrecht 1899: fig. 3, Taf. 2) 17-segmented, 210 µm long, with an aesthetasc on segment 16 and geniculation located between segments 15 and 16. Maxilliped (see Giesbrecht 1899: fig. 12, Taf. 2) with thorn-like process in proximal-half of basis. Sixth leg (see Giesbrecht 1899: fig, 15, Taf. 2) forming large opercular plate closing off genital apertures, armed with 2 setae.

Hosts. The most common host of Asterocheres suberitis is the hermit crab sponge Suberites domuncula (Olivi) [domunculus = "little house"], which is a Mediterranean species that typically grows on an empty snail shell or a shell occupied by a snail or hermit crab and less commonly on other substrates such as bivalve shells or wharf pilings ( Riedl 2000). Suberites domuncula hosts other siphonostomatoid copepods such as Sponginticola uncife r Topsent, 1928 and Asterocheres simulans ( T. Scott, 1898) ( Topsent 1928; Ivanenko 1997). Recently, Mariani & Uriz (2001) found A. suberitis associated with other sponge species such as the widespread Cliona viridis (Schmidt) , Scopalina sp. and the Mediterranean Scopalina lophyropoda Schmidt. However , these authors recognized that their copepod identification must be treated with caution.

Distribution. Mediterranean ( Giesbrecht 1895; Mariani & Uriz 2001), north Atlantic (according to Stock (1967) and Gotto (1993) the form referred to as A. echinicola by T. Scott (1898, 1900) and Norman & T. Scott (1906) from the Clyde and Loch Fyne almost certainly belong to A. suberitis ), and India ( Krishnaswamy 1959—this record requires confirmation).

Remarks. Giesbrecht (1895) collected this species from Suberites domuncula (Olivi) from Naples, but reported it under the binomen Cyclopicera echinicola Norman, 1868 . Giesbrecht (1897) subsequently realised that his specimens from S. domuncula were not conspecific with C. echinicola and renamed it Asterocheres suberitis .

Our examination of Giesbrecht´s (1897) cotypes revealed the following errors in his original and subsequent descriptions: 1) the antennal endopod is composed of 3 instead of 2 segments as illustrated by Giesbrecht (1899); 2) the mandibular palp is clearly 2-segmented and not 1-segmented as depicted in the original illustration; 3) the ornamentation of the inner lobe of the maxillule was overlooked by Giesbrecht (1899); and 4) legs 2 and 3 were never illustrated by Giesbrecht (1897, 1899).

This species, like A. intermedius discussed above, belongs to the group of congeners with 21-segmented antennules in females. However, A. suberitis can be distinguished from other members of this group as follows. Asterocheres suberitis can be easily separated from A. lilljeborgi , A. simulans (see Ivanenko 1997), A. bacescui , A. jeanyeatmanae , A. reginae and A. lunatus (see Johnsson 1998) by lacking a dorsoventrally flattened prosome. Asterocheres suberitis , like most Asterocheres species, possesses a siphon reaching the maxilliped base. In contrast, the siphon of A. ellisi , A. urabensis , A. hirsutus , A. intermedius , A. tenerus and A. astroidicola extends to leg 1 or 2. Asterocheres suberitis has caudal rami 1.5 times longer than wide, while in A. tenuicornis and A. echinicola they are 6 and 2.5 times longer than wide, respectively, and in A. flustrae it is about as long as wide. Asterocheres uncinatus has a 2-segmented endopod on the antenna (see Marcus & Por 1960 and Marcus 1965), while A. suberitis has 3 segments on this appendage. The 2-segmented mandibular palp of A. suberitis separates it from A. minutus , A. violaceus and A. madeirensis , each having a 1-segmented mandibular palp.

In 1903, T. Scott collected some Asterocheres specimens from Scotia Bay (South Orkneys) which in his opinion closely resembled A. suberitis . Although he reported some differences between them, such as the shape of the siphon, the length of the fifth leg, and the proportional lengths in the antennulary segments and abdominal somites, he considered that these differences were not sufficient enough to establish a new species, and therefore, named the Scotia Bay specimens Asterocheres suberitis antarctica . However, comparisons between the illustrations of these two forms revealed another difference: the antennary exopod of the Scotia Bay specimens bears “two or three short terminal bristles” rather than a small medial seta and 2 terminal setae, one of them very long, as in A. suberitis . Thus contrary to T. Scott’s opinion, we consider that these two forms are not conspecific and that the differences enumerated above are enough to separate them at species level. Nevertheless, as A. s. antarctica material is no longer extant, the establishment of a new species must be postponed until more specimens are collected.

Figures

FIGURE 1. Asterocheres suberitis, Giesbrecht, 1897, cotype female. A, antenna; B, mandible; C, maxillule; D, leg 2; E, leg 3.