Cymodoce Leach, 1814

Khalaji-Pirbalouty, Valiallah, Bruce, Niel L. & Wägele, Johann-Wolfgang, 2013, The genus Cymodoce Leach, 1814 (Crustacea: Isopoda: Sphaeromatidae) in the Persian Gulf with description of a new species, Zootaxa 3686 (5), pp. 501-533 : 502-505

Genus Cymodoce Leach, 1814

Cymodoce Leach, 1814: 433 .— Dumay, 1972b: 642.— Kussakin, 1979: 417.— Harrison & Holdich, 1984: 301.— Schotte & Kensley, 2005: 1243.

Type species: Cymodoce truncata Leach, 1814 ; by monotypy.

Diagnosis. Body vaulted, dorsal surfaces with nodular ornamentation, folds at pereonite 5; strongly sexually dimorphic. Pleon sutures (except first) running to lateral margin, all separate, sutures long. Pleotelson vaulted, anteriorly as wide as pleon, with paired submedial bosses or with paired longitudinal carinae; posterior margin trilobate and with two longitudinal bilateral grooves, with ventral thickened rim; lateral margins forming ridge. Epistome anteriorly acute, with median constriction, elongate. Maxilliped palp articles 2–4 medial margins extended, forming finger like lobes, article 2 not expanded; endite distal margin truncate. Pereopods 1 (or 1–3), inferior margins of merus, carpus and propodus palm with close-set conspicuous RS along inferior margins. Penial processes entirely separate, basally set apart, long (extending to distal part of pleopod rami), tapering smoothly from base, apex bluntly rounded. Uropodal exopod lamellar, distally acute, lateral margin with thick upturned rim; endopod lamellar, thicker than exopod, distally truncate or acute (Atlantic species) or rounded in section (Indo- Pacific species).

Description. Head rostral point dorsally visible, simple, separating antennular bases; anterior margin simple, without paired incisions in front of eyes, lateral margins not laterally extended to body outline (antennules more or less ventral). Eyes large, dorsolateral, posteriorly lobed. Pereonite 1 lateral margins not anteriorly produced, not laterally enclosing head, pereonites 2 or 5–7 with posterior margin not raised, anteriorly without keys. Pereonite 6 simple, without bosses, processes or marginal extensions. Pereonite 7 as wide as pereonite 6, forming part of body outline, dorsally without bosses, processes or marginal extensions, laterally with a posterior depression. Coxae 2–4 distally narrow and rounded; those of pereonite 6 not large, not overlapping those of pereonite 7. Pleon consisting of 4 visible segments (as determined by lateral sutures); pleonite 1 entire, posterior margin even, as wide as remainder of pleon, extending to pleon lateral margins; dorsal surface without process; posterior margin with two distinct submedian lobes, without 'keys'.

Antennule peduncle with basal articles medially not in contact, peduncle articles 1 and 2 robust, article 3 elongate, slender; article 1 not produced; article 2 approximately 0.5 as long as article 1; articles 2 and 3 colinear; flagellum approximately as long as peduncle, flagellar articles 4 or 5 and subsequent each bearing a pair of aesthetascs.

Antenna peduncle articles all colinear (or curving regularly), less robust than antennule, peduncular articles all of similar thickness.

Left mandible incisor wide ( Fig. 1 A); lacinia mobilis and spine row present. Right mandible ( Fig. 1 B–D) lacinia mobilis absent or represented by a modified distally trifurcate spine. Maxillule lateral lobe with RS some or all serrate, mesial lobe with 4 major RS, these setae being heavily serrate.

Maxilla ( Fig. 2 A, B) with serrated setae on middle and lateral lobes.

Pereopod 1 ( Fig. 2 E, F) ambulatory. Pereopod 2 similar in proportion to pereopod 3. Pereopods with inferior margins of ischium to carpus not bearing dense setulose fringe.

Pleopod 1 rami not operculate; exopod lamellar; exopod with longitudinal axis weakly oblique; endopod of similar proportions to exopod, mesial margin lamellar, distally triangular, endopod proximomedial heel absent; exopod distally subtruncate or truncate, distal margins not serrate. Pleopod 2 endopod about as long as exopod; exopod distal margins not deeply serrate; appendix masculina inserted sub-basally, with straight margins, about as long or longer than endopod, distally acute. Pleopod 3 exopod transverse suture present, endopod of similar proportions to exopod. Pleopod 4 rami without PMS; exopod transverse suture present, thickened transverse ridges absent, lateral margin with short simple marginal setae; endopod thickened transverse ridges present; mesial margin without deep distal notch; without proximomedial lobe. Pleopod 5 ( Fig. 2 C, D) exopod transverse suture present, entire, thickened transverse ridges absent, lateral margin with short simple setae, with 5 discrete patches (3 distally and 2 under transverse suture); endopod with thickened transverse ridges present, with proximomedial lobe.

Uropod rami not strongly flattened, not forming part of continuous body outline; exopod (of adult male) similar in length to endopod.

Female. Body ornamentation reduced or absent, dorsum smooth. Mouthparts metamorphosed. Marsupium formed from 4 pairs of oostegites, anterior pocket absent, posterior pocket absent, oostegites overlapping at midline. Pleotelson weakly bi-domed; posterior margin weakly tri-lobed with median lobe usually overriding lateral lobes; ventral exit channel weakly developed.

Remarks. The genus Cymodoce is most readily identified using male characters, females usually being identified by association. Males have a characteristic rugose, often setose dorsal surface, particularly on the pleon and pleotelson; the posterior margin of the pleotelson can be described as trilobed or with two sub-median excisions ( Figs 3 A, 8A, 12A, 16A); all species have a large flat (laminar) uropodal exopod, always more than half the length of the endopod but not longer than the endopod. Typically the pleotelson is bidomed or variously bicarinate, with several species having a prominent boss just anterior to the posteromedian lobe of the pleotelson, this boss occasionally with a spine (e.g. Cymodoce pelsarti Tattersall, 1922 [see Harrison & Holdich 1984, fig. 14]). The pleon has four sutures all running to the lateral margin. The maxilliped has elongate mesial projections on palp article 2–4, the penes are elongate, extending most of the length of the pleopod and are unfused; the appendix masculina is basally inserted and approximately as long as the endopod and not reflexed.

Several of these characters, such as strong sexual dimorphism, metamorphosed mouthparts (see Harrison and Holdich 1984), maxilliped morphology, pereopod setation, morphology of pleopods 1 and 2, are shared with genera such as Cilicaea , Paracilicaea and Cilicaeopsis , and the females of these genera are very similar to females of Cymodoce . These genera are all separated from Cymodoce by the reduction of the uropodal endopod to a stub and a cylindrical uropodal exopod as well as having prominent pleonal processes in Cilicaea and Cilicaeopsis .

Cymodoce is one of the first described of the sphaeromatid genera and has unsurprisingly accumulated a large number of species over two centuries. The first restrictive diagnosis to the genus was given by Harrison and Holdich (1984), who commented that the genus was an “ unreasonably large taxonomic repository containing many unrelated species ”. In their discussion of the included species, Harrison and Holdich (1984) excluded a large number of species from the genus sensu strictu. Bruce (1997) removed a further five species previously housed in Cymodoce to a new genus, but otherwise the situation remains unchanged since Harrison and Holdich’s (1984) review.

The generic diagnosis and description presented here are more detailed than has been previously presented, and is derived from a character data set for all sphaeromatid genera, the data being primarily obtained from the type species. Applying this description to the species placed in combination with Cymodoce results in nearly threequarters (50 of 72) of the species being excluded from the genus as incertae sedis and as species inquirenda. This situation has remained largely unchanged since Harrison & Holdich’s (1984) review and the later appraisal ( Harrison & Ellis 1991) that the genus contained 23 species, possibly 32. Certain groups with the genus, notably all the South African species, all New Zealand species and several of the southern Australian species, need to be described in detail and reallocated to other genera. See Appendix 1 for a list of those species previously placed in combination with Cymodoce , but regarded here as incertae sedis or species inquirenda.

Figures

FIGURE 1. SEM, A – B, Cymodoce fuscina Schotte & Kensley, 2005, (SNM, 39654); A, left mandible; B, right mandible; C – D, C. richardsoniae Nobili, 1906 (SMF- 3481) right mandible (In: Incisor; Lm: lacinia mobilis; Sr: Spine row; Mp: Molar process).

FIGURE 2. SEM, A – D, Cymodoce tribullis Harrison & Holdich, 1984, (Museum of Tropical Queensland, W 31864); A, detail of pectinate setae, lateral endite; B, maxilla, mesial endite; C, D, detail of medial scale patch of pleopod 5; E – F, Cymodoce sp., (from Persian Gulf); E, pereopod 1, merus inferior margin; F, pereopod 7, carpus distal margin.

FIGURE 3. Cymodoce truncata Leach, 1814. Lectotype (BMNH, 1979. 439. 1); A, dorsal view; B, lateral view; C, antennule; D, antenna; E, epistome; F, female (BMNH, 1979: 418.1).