Thalamocyclops pachypes, Fiers & Van Damme, 2017

Fiers, Frank & Van Damme, Kay, 2017, Thalamocyclops pachypes gen. nov., sp. nov. (Copepoda: Cyclopoida: Cyclopidae), a crevicular cyclopine from Socotra Island (Yemen): tale of a remarkable survival drive, Journal of Natural History 51 (41 - 42), pp. 2463-2507 : 2466-2489

publication ID	https://doi.org/ 10.1080/00222933.2017.1344328
publication LSID	lsid:zoobank.org:pub:9ADC9001-1B11-4843-9A49-4B94675DFB33
persistent identifier	https://treatment.plazi.org/id/03C7290D-EE62-7F15-FE53-C311FC98FB73
treatment provided by	Felipe
scientific name	Thalamocyclops pachypes
status	sp. nov.

Treatment

Thalamocyclops pachypes sp. nov.

( Figures 1–13 View Figure 1 View Figure 2 View Figure 3 View Figure 4 View Figure 5 View Figure 6 View Figure 7 View Figure 8 View Figure 9 View Figure 10 View Figure 11 View Figure 12 View Figure 13 )

Material examined

Holotype female, adult, dissected with the appendages mounted on seven slides (RBINSc COP 5309 View Materials A–G), allotype, adult, dissected with appendages mounted on seven slides (RBINSc COP 5310 View Materials A–G); paratypes: one female, three males and 70 copepodids and six nauplii ethanol-preserved (RBINSc COP 5308 View Materials ), two females (RBINSc COP5311 View Materials A-I, COP 5312 View Materials A–G), eight copepodids dissected (RBINSc COP 5313–5320 View Materials ).

Type locality

Socotra Island ( Yemen), Diksam Plateau (central coörd.: 12°31.50 ʹ N 53°58.00 ʹ E) at 700 m above sea level; limestone weathered crevices, inhabited by Socotra pseudocardisoma Cumberlidge & Wranik, 2002 ( Decapoda : Brachyura: Potamidae ), coll. M. Apel, (Museum Mensch und Natur, München, Germany), 26 October 2000.

Etymology

The specific epithet pachypes is a conjuction of the words pachis (Greek meaning: thick) and pes (Latin meaning: leg), and refers to the unique swollen shape of the female leg 5 and of the leg 4 endopodite and protopod distinguishing the species from its congener T. soqotraensis comb. nov.

Description of the adults

Female. Habitus ( Figure 1 View Figure 1 (a,b)) compact, dorsoventrally compressed, with clear division between prosome and urosome, both equally long; no pseudosomite defined; fifth leg pediger and genital double somite laterally expanded; body length between 815 and 840 μm (holotype 825 μm), with largest width (280–295 μm) near posterior margin of cephalothorax; posterior margins of all somites straight; integument without particular modifications (pits or refractile points), but apparently clothed with a dense carpet of short cilia (not illustrated); ovigerous females with pair of egg sacs positioned dorsolaterally, each containing four eggs.

Genital double somite ( Figure 2 View Figure 2 (d–f)) wider than long, with lateral margins expanded laterally and ventrally delineating a ventral space around copulatory area; vestigial leg 6 situated in middle of somite, dorsolaterally positioned; copulatory pore opening in caudal half of ventral surface, leading to receptacle with duct fitted in triangular shaped muscular mass; receptacle compacted centrally, anterior part expanded, posterior part apparently not present; urosomites 4, 5 and anal somite short, and parallel sided; anal operculum short, not extended, crescentic, with smooth border; anal somite set with few widely spaced small spinules along half of posteroventral margin.

Caudal rami ( Figure 2 View Figure 2 (d–f)) flattened, oval in cross-section, about twice as long as wide in dorsal view and parallel to each; six setae: anterolateral one inserted in median third, posterolateral one near outer distal edge; dorsal seta short, biarticulated, arising near to caudal margin; outer and inner terminal setae sturdy but well developed (outer 190 μm, middle 250 μm), bipinnate, with breaking plane; inner terminal seta, pinnate and slightly longer than half ramal length. Spinules present at insertion of posterolateral seta only.

Rostrum ( Figure 1 View Figure 1 (a,b)) large, wide and linguiform; bent ventrally at right angle to longitudinal body axis; no integument modifications visible.

Antennule ( Figure 3 View Figure 3 (c)) short, reaching only halfway along cephalothorax; 10-segmented appearance, but with segments 1 and 2 incompletely separated; integument of each segment smooth; segmental armament (first and second segment considered separated): 1[6]-2[7]-3[2]-4[1]-5[2]-6[3]-7[2 + Aesth]-8[2]-9[2 + Aesth]-10[7 + Aesth]; element on segment 4 short and conical; aesthetasc on segment 7 linguiform, on segment 9 filiform, and on segment 10 slender and filiform.

Antenna ( Figure 3 View Figure 3 (a,b)) four-segmented; coxobasis with single abexopodal seta, but without exopodite; endopodite with one, five and seven setae, respectively; outer apical element on second endopodite segment stout; coxobasis with three transverse lines of minute spinules in proximal half of frontal surface, caudal surface unadorned; endopodite segments with typical spiniform ornamentation along outer margin.

Labrum ( Figure 4 View Figure 4 (f)) with prominent blunt corners, 10 blunt medial teeth, and pair of hairy pads. Mandible ( Figure 4 View Figure 4 (a,b)) with slender gnathobasis, with undifferentiated palp, represented by a single robust seta; masticatory margin with sharp teeth in upper half, two cuspidate combs and one short seta; gnathal margin accompanied with a median row of long spinules. Maxillule ( Figure 4 View Figure 4 (c)) with typical cyclopine appearance; arthrite with three robust smooth claws and a single robust seta along medial edge; lateral margin with six elements, outermost large and wide, bipinnate; maxillular palp with normal armament of three endopodal, one exopodal and three medial setae; endopodite articulating. Maxilla ( Figure 4 View Figure 4 (g– j)) with incompletely fused syncoxa, bearing three endites with normal armament; distal margin of syncoxa, on frontal side, with linguiform protuberance reaching beyond margin; basis typically with claw, a medial proximal and a frontal element; claw rather short and robust, with long spinule row on frontal side; endopodite two-segmented with two and three elements on proximal and distal segments, respectively. Maxilliped ( Figure 4 View Figure 4 (d,e)) four-segmented, compact, less than half as long as maxillar syncoxa; armament (proximal to distal segment): 2, 1, 1, 2; all setae, except one on proximal segment, conspicuously long and bipinnate; proximal segment with spinule row on frontal surface, second segment with several spinule rows near inner margin on frontal surface and one near outer distal edge on caudal face.

Legs 1–3 ( Figure 5 View Figure 5 (a–c)) with short sturdy two-segmented rami; prae-coxal flap in leg 1 robust, slender in legs 2–3 (not illustrated); intercoxal sclerite with large and acute processes with narrow median gap in leg 1 but widely spaced in legs 2 and 3; coxa of leg 1 with long bipinnate medial seta; coxa of legs 2 and 3 without medial element; surface of coxa smooth in leg 1, set with spinule row near distal outer edge on caudal surface in legs 2 and 3; medial margin of basis crescentic and set with hairs (leg 1) or slender spinules (legs 2 and 3); medial spine on basis of leg 1 present, serrate; leg armature summarized in Table 1.

Leg 4 ( Figure 6 View Figure 6 (a,b)) with two-segmented exopodite, one-segmented endopodite and a robust general appearance; coxa without medial seta and smooth surfaces; intercoxal sclerite with large acute processes widely spaced medially; basis with large irregular ovate structure along distal margin between ramal insertion; medial margin crescentic, flat in anterior view, partially inflated on caudal surface; medial margin set with stiff spinules; exopodite as in the preceding legs, except for shorter aspect of inner setae; endopodite one-segmented, large, robust and roughly ovate; anterior surface flat, caudal surface with an inflated ovate region in proximal half; armament elements short and robust, all bipinnate, both terminal elements equally sized.

Leg 5 ( Figure 2 View Figure 2 (a–c)) represented by a large and wide lateral outgrowth of leg bearing somite, completely confluent with pediger, and inclined backward; segment with three rigid armature elements: two setiform ones (seta representing original basal segment and outer element of original distal segment) and one short conical element (homologous with inner element of original distal segment).

Leg 6 ( Figure 2 View Figure 2 (d,e)) rigidly sclerotized plate with three smooth elements along border: outer one longest, median one short and conical, and medial one half as long as outer element.

Male. Habitus ( Figure 1 View Figure 1 (c)) dorsoventrally compressed, as in female, but metasomal somites tapering more sharply caudally; sixth leg bearing somite longer than wide, barrel-shaped; posterior urosomites parallel sided; caudal rami flattened as in female, less wide, and slightly tapering caudally; armature as in female; body length 800–840 μm.

Antennule ( Figure 3 View Figure 3 (d)) typically bigeniculate cyclopid shaped, composed of 15 segments each rigidly sclerotized; teminal segment with straight and blunt distal part; armature distribution as follows: 1(7 + 3Aesth)-2(4)-3(2)-4(2 + Aesth)-5(1)-6(2)-7(2)-8(1)- 9(2)-10(4)-11(2)-12(?)-13(1 + 1T)-14(2T)-15(11 + 2Aesth); aesthetascs on segments 1, 4 and 11 decomposed, represented by their pedestal only, aesthetascs on other segments not observed, except two filiform ones on ultimate segment; setae on segments 1–9 with remarkable sturdy appearance, sparsely pinnate.

Mouthparts and leg 1 and 2 as in female. Leg 3 ( Figure 5 View Figure 5 (d,e)) with protopodite, exopodite, and proximal endopodite segment as in female; distal endopodite segment with five elements only: inner terminal female homologous element absent; outer terminal spine smooth, blunt and arched; inner subdistal element rigid, smooth and half as long terminal spine; outer and both inner proximal elements bipinnate; ancestral position of (lost) inner terminal armature element marked as a small internal dense spherical mass below distal margin of segment (not illustrated). Leg 4 ( Figure 6 View Figure 6 (c)) unmodified, with two-segmented rami; second endopodite segment with short terminal outer spine and long inner bipinnate inner seta; armature of legs summarized in Table 2.

Leg 5 ( Figure 6 View Figure 6 (d)) basically as in female except for the more rectangular shape of the setae-bearing extension, and its ventrally positioned location on the pediger; apical elements of original distal segment of same nature as in female but distinctly longer, inner one serrate.

Leg 6 ( Figure 6 View Figure 6 (d)) represented as a rigid triangular smooth plate bearing 3 appendages: outer and median one setiform, inner one spiniform and serrate.

Development

Complete sets (stages I to V, females and males) of the copepodid stages were present, as well as several nauplii. However, the complete morphological development of the naupliar stages could not be reconstructed. An example is illustrated ( Figure 7 View Figure 7 (a,b)) demonstrating the extreme flattened body shape and the presence and position of an integumental window on the head shield. The nauplius, at least the older stadia, is feeding. A thin-walled internal tube stretching from mouth to anus is visible.

Description of the copepodids

Habitus ( Figure 7 View Figure 7 (a–e)). The body develops through the usual five copepodid stages: from stage I with five body somites to stage CV (pre-adult stage) composed by nine somites; length increases from 350 μm in stage CI to 960 μm in stage CV (maximum, CV stage somewhat longer than adult); both sexes (recognizable in stages CIV and CV) equally sized; prosome and urosome clearly differentiated in stages CIV and CV.

Caudal rami with six armature elements in all stages: two lateral and three terminal ones, and a biarticulate dorsal seta; rami rather short (1.5 times longer than wide) in stage CI ( Figure 8 View Figure 8 (a,b)), with irregular medial margin; terminal armature elements inserted along caudal margin: outer one shorter than ramus, middle one 1.5 times longer than ramus, and inner one longest (at least three times longer than middle one, broken in all specimens); breaking plane absent; caudal rami in stage CII ( Figure 8 View Figure 8 (c)) 1.5 times longer than wide, with outer terminal seta twice as long as ramus, middle one fully developed, and inner one only slightly longer than ramus; breaking plane present in middle seta only; setal armament as in adult in stages CIII–CV.

Female antennule ( Figures 9 View Figure 9 (d,e) and 10(a–c)). Number of segments evolves in the successive copepodid stages from six-segmented (Stage CI) over seven-segmented (stage CII) and nine-segmented (stage CIII) to the adult ten-segmented shape in stages CIV and CV.

Terminal (sixth) segment of the stage CI antennule possesses, apart from its setal complement, an apical hyaline lip-shaped structure that disappears during the moult to stage CII and remains absent in the following stages; aesthetascs present from stage C1 on (segments 3, 5, 6) being filiform; linguiform shape of aesthetascs appears first in stage CII on segment 4 (=segment 3 in stage C1) and on segment 7 (terminal segment); aesthetasc on segment 5 of stage CI remaining filiform through successive stages up to and including the adult; setal presence in successive stages summarized in Table 3; growth by segment addition resulting from the subdividing of the antennular segments of stage CI: first

segment (in moult from stage CII to CIII) and stage I second segment (in moults from stage CI to CII, from stage CII to CIII, and from stage CIII to CIV); segmentation between segments 1 and 2 in stage CV disappearing partially during terminal moult (CV to adult: dashed line in Table 3).

Male antennule ( Figure 11 View Figure 11 (a,b)). Before stage CIV, no differences in shape and setation between male and female antennule copepodid antennules observed; stage CIV of male antennule resembling female stage CIV antennule, except for the slightly more robust appearance of the segments and the presence of a small additional (hyaline) protuberance on segment 6; moult between stage CIV and CV affecting the antennular shape and armament drastically: separation of stage CIV antennulary segments 3 and 4, and 5 and 6 is deleted (resulting in eight-segmented antennule), number of setae on segment 2 increases (see Table 4), and protuberances on segments 4 and 5 increase in number and shape; armament evolution is summarized in Table 4.

Antenna and mouthparts ( Figure 9 View Figure 9 (a–c)). Antenna biramous at stage CI with a threesegmented endopodite and a non-segmented exopodal process composed of a cluster of cells forming a cylindrical outcrop with two slender setal elements inserted vaguely in the middle of cellular mass; basipodite and endopodite resembling adult morphology but latter with fewer setae (four on second endopodite segment, six on third segment); exopodal cellular mass and additional setal elements absent from stage CII onward; adult number of seta (five) on second endopodite segment present from stage CIII on, adult number of setae (seven) on terminal endopodite segment present from stage CIV.

Mandible, maxillule and maxilla and associated labrum completely shaped from stage C1 on, resembling the adult morphology in every detail; maxilliped in stage 1 represented as a small bud (about one-quarter of maxillary length) with four long setal appendages along inner side; maxilliped as in adult from stage C2 on.

Development of legs 1–4 ( Figures 12 View Figure 12 and 13 View Figure 13 ). Leg development (i.e. segment differentiation and setal additions) truncated as in Bryocyclops caroli Bjornberg, 1985 , tabulated in Ferrari (1988).

Subdistal outer spine on exopodite of leg 3 narrow and unarmed in stage CII ( Figure 12 View Figure 12 (e)), being reshaped as normal spine in stage IV ( Figure 13 View Figure 13 (a)); subdistal exopodite spine of leg 4 displaying same development constraint (in stage CIII – Figure 13 View Figure 13 (b) and stage CIV – Figure 13 View Figure 13 (c)).

Sexual differences of leg 3 endopodite apparently not expressed during development; terminal moult affecting male leg 3 only, including modification of terminal outer spine and deletion of terminal inner element; differences of leg 4 endopodite between male and female distinct in stage CV but not pronounced: female endopodite wider than in male, one-segmented but with clear remnant of articulation as transverse cuticular ridge between former proximal and distal segment, without spinule patterns along former articulation ( Figure 13 View Figure 13 (e)); armature elements similar in both sexes.

Development of legs 5 and 6 ( Figures 8 View Figure 8 and 11 View Figure 11 ). Leg 5 (precursor) appearing as a lateral triangular outgrowth in stage CII ( Figure 8 View Figure 8 (c,d)), reshaped in a large rectangular lateral lobe with a distal spine and a subdistal (dorsally located) seta in stage CIII ( Figure 8 View Figure 8 (e)); leg 5 represented by three armature elements in stage CIV and CV: two terminal elements (spine and seta) on a ventrolateral square outgrowth and one lateral setal element inserted on the posterior border of the somite (dorsally located); ventrolateral lobe reappearing almost unmodified in female copepodid CV, but being narrower and longer in male copepodid CV.

Leg 6 recognizable as lateral triangular outgrowth in stage CIII ( Figure 8 View Figure 8 (e)), present as a truncated triangular lobe, armed with a large spine and a short seta, in stage CIV ( Figure 8 View Figure 8 (f)), and bearing three armature elements in stage CV (one spine, two short setal elements); female leg 6 in stage CV confluent with border of somite and located dorsolaterally ( Figure 11 View Figure 11 (c)); male leg 6 in stage CV present as a distinct ventrolateral crescentic outgrowth in the male ( Figure 11 View Figure 11 (d)).

Comments

The naupliar body shape is remarkably flattened compared with the nauplii known of other Cyclopidae (see Dahms and Fernando 1994; Karaytug and Boxshall 1996; Dahms 2000). The presence of a dorsal integumental window in cyclopine nauplii has not been documented previously. Body shape must be a particular adaptation to the cramped habitat in which it occurs. The window indicates extensive osmoregulatory activity as a response to the environmental conditions in the hole ( Hosfeld 1999).

An antennary exopodal structure in the first copepodid (CI) has been documented for other cyclopines (see development of Paracyclops fi mbriatus ( Fischer, 1853) in Karaytug and Boxshall 1996; personal observations) and is also present in the first copepodid stage of T. pachypes sp. nov. The exopodal structure is an outgrowth of clustered cells, not wrapped within a chitinous membrane, with the two setae arising from an insertion location between the cellular masses. Mouthparts in stage CI cyclopine copepodids resemble the adult morphology closely but differ still in details of the ornaments, with the most conspicuous difference between stage CI and the successive stages, the presence of a mandibular palp structure (cellular mass) in the former. In contrast, the mandible, maxillule and maxilla in stage CI of T. pachypes sp. nov. are identical to those in the adults. The mandible lacks the undifferentiated cellular mass known to occur in other cyclopines in stage CI, bearing solely the short seta, as in the adults. The maxilliped, normally well developed in stage CI cyclopines and resembling the adult morphology (less one or two seta short), is far from being clearly differentiated in stage CI of T. pachypes sp. nov. From stage CII, the maxillipedal body is larger, equipped with an adult complement, but retains still the truncated appearance as in stage CI.

The successive modification of the legs during the copepodid development is similar to the development in other cyclopines ( Ferrari and Dahms 2007). Leg development, including the evolution of legs 3, and the vestigial legs 5 and 6, is similar in male and female copepodids although the expression of them is considerably different in the adults. The endopodite of the female leg 4 has a more robust and compact appearance in stage CV than in the male at the same stage. Although both segments are coalescent in the female CV, the (ancestral) division line between them is clearly present as an integument structure and the four armature elements still have the conventional structure (three long pinnate setae and a serrate spine) and location (i.e. 1.I.2).

Thalamocyclops soqotraensis ( Mirabdullayev, Van Damme & Dumont, 2002) comb. nov.

( Figures 14–16 View Figure 14 View Figure 15 View Figure 16 )

Bryocyclops soqotraensis sp. nov. – in Mirabdullayev, Van Damme & Dumont, 2002: 264–266, figs 2–23.

Bryocyclops (Bryocyclops) soqotraensis Mirabdullayev, Van Damme & Dumont, 2002 ; Dussart & Defaye, 2006: 151.

Material examined

Female holotype dissected and mounted on a single slide (RBINSc COP 4492 View Materials , labelled ‘type’), paratype female and paratype male (RBINSc COP 4493–4495 View Materials ), dissected; all glycerine mounted and sealed with polyurethane varnish .

The complete description of this species has to be consulted in Mirabdullayev et al. (2002). The following amendments deal with certain morphological details in order to compare T. soqotraensis with T. pachypes sp. nov.

Female. Genital double-somite ( Figure 14 View Figure 14 (a,b)) wide, about 1.4 times wider than long (ratio of mounted urosome), and longer than following urosomites combined; lateral margins arched; lateral margins; posterior margins of genital double-somite and following urosomites with wide, irregularly undulated hyaline fringe; integument of cephalothorax and following somites, including caudal rami naked, devoid of structural ornaments; copulatory pore situated in middle of ventral surface of double-somite, directly leading to ovate field of compact tissue; anterior receptacle wide, only slightly expanded anteriorly; caudal receptacle not visible.

Anal operculum triangular, reaching beyond anal area, with serrate margins and transverse row of spinules on underside; posterior margin of anal somite without ornamentation dorsally, set with rigid spinules laterally and ventrally.

Caudal rami ( Figure 14 View Figure 14 (a,b)) cylindrical, only slightly tapering caudally (cylindrical appearance in Figure 14 View Figure 14 (b) results from inclined position on slide), rami widely separated from each medially, and diverting; lateral seta inserted in middle of margin, without spinules at its insertion; distal lateral element spiniform, serrate along its outer margin, plumose at the inner margin; insertion of distal lateral element set with robust spinules; terminal principal ones with breaking plane; medial terminal seta somewhat shorter than inner medial margin of ramus, setiform; dorsal seta about twice as long as ramus.

Antennule ( Figure 15 View Figure 15 (b)) 10-segmented (ancestral segments VI to IX fused) with following armature:1[6]-2[7]-3[2]-4[1]-5[2]-6[3]-7[2 + Aesth]-8[2]-9[2 + Aesth]-10[7 + Aesth]; aesthetascs on segments 7 and 10 lingiform, aesthetasc on segment 9 filiform; setal armament flexible, finely pinnate; first segment without spinular ornamentation. Antenna ( Figure 15 View Figure 15 (a)) rather slim, not compact, without exopodite and a single abexopodal element; first endopodite segment with one seta, second segment with five setae, and terminal segment with six terminal setae; mandible ( Figure 15 View Figure 15 (c)) with multi-cuspidate masticatory margin; palp absent, represented by single short seta. Maxillule ( Figure 15 View Figure 15 (e)) typical cyclopid with separate endopodite and with five smooth and one pinnate element along lateral margin of arthrite. Maxilla ( Figure 15 View Figure 15 (d)) with two-segmented endopodite, bearing two spiniform elements on proximal segment, one spiniform and two short naked elements on distal segment. Maxilliped ( Figure 15 View Figure 15 (f,g)) four-segmented, penultimate one with single, pinnate element, ultimate segment with two naked setae.

Legs 1–4 as described in Mirabdullayev et al. (2002); setal armament sturdy, lanceolate; ornaments along inner margin of exopodites and outer margins of endopodites ( Figure 16 View Figure 16 (b,d)) hairy.

Leg 5 ( Figure 14 View Figure 14 (a)) completely confluent with the pediger, represented by three armature elements; seta representing basal segment inserted laterally on somite; armament representing original distal segment arising from large truncated outgrowth of pediger; ventrally located and caudally directed; outer element, slightly subdistally inserted, setiform, inner one robust, spiniform and serrate; both elements both equally long.

Leg 6 vestiges ( Figure 14 View Figure 14 (b)) located dorsally in anterior half of genital double-somite; leg vestige rigidly sclerotized, bearing three smooth and short armature elements, middle one shorter than both others.

Male. Urosomites ornamentated as in female, but second and third ones not fused. Leg 5 ( Figure 14 View Figure 14 (c)) basically as in female, process representing distal segment less wide. Leg 6 vestiges ( Figure 14 View Figure 14 (c)) symmetrical, rectangular, rigid with smooth surface; outer posterior edge slightly expanded, bearing three elements: medial one spiniform (smooth?), middle and outer one sturdy setiform.

Antennule ( Figure 16 View Figure 16 (a)) 17-segmented with terminal segment complexes [XXIV– XV] and [XXVI–XXVIII] separated; setal armament as in T. pachypes , but elements less sturdy; first segment with three linguiform aesthetascs, segments 4, 9 and 12 each with one linguiform aesthetasc, all of moderate length; segment 16 and 17 each with one short filiform aesthetasc (bithek of ultimate segment lost on antennule in Figure 16 View Figure 16 (a)). Mouthparts, leg 1 and 2, and exopodite of legs 3 and 4 as in female.

Leg 3 endopodite ( Figure 16 View Figure 16 (c)) inner proximal pair of setae on second segment setiform, proportionally shorter than in female; inner subdistal and inner distal one setiform armed with short sturdy setules; outer distal element long, hook-shaped, with serrate rounded expansion in distal half of outer margin. Leg 4 endopodite ( Figure 16 View Figure 16 (e)) distinctly two-segmented, with armament as in female.