Gamispatulus schizodontis Thatcher & Boeger, 1984

Narciso, Rodrigo B. & Silva, Reinaldo José Da, 2020, Two Gamispatulus Thatcher & Boger, 1984 (Cyclopoida: Ergasilidae) from Schizodon intermedius Garavello & Britski (Actinopterygii: Anostomidae), with description of a new species, Zootaxa 4803 (3), pp. 463-482 : 465-471

Gamispatulus schizodontis Thatcher & Boeger, 1984

(Figs. 1–4)

Host. Schizodon intermedius Garavello & Britski, 1990 (Anostomidae)

Locality. Veados River , Jurumirim Reservoir, Upper Paranapanema River (23° 16′2.49″ S, 48° 38′15.72″ W), municipality of Itatinga, São Paulo State, Brazil .

Additional locality. Paranapenema River , Jurumirim Reservoir, Upper Paranapanema River (23° 29′16.54″ S, 48° 37′12.88″ W), municipality of Angatuba, São Paulo State, Brazil .

Site in host. Nostrils.

Specimens deposited. INPA 2526 to INPA 2529 (12 adult females) deposited in the Invertebrate Collection of the Instituto Nacional de Pesquisas da Amazônia ( INPA), municipality of Manaus, Amazonas State, Brazil .

Prevalence and mean intensity in nostrils: 21 infect hosts in 28 analyzed fish (or 75%) and 17 ± 4,5 copepods per infected fish.

Prevalence and mean intensity on the gill filaments. None of the 28 analyzed fish.

Description of adult female. Based on 12 female specimens, no males observed. Body cyclopiform (Fig. 1A), comprising prosome, urosome, and caudal rami; prosome consisting of cephalosome and PS-1; PS-1 fused to cephalosome; and 3 free pedigerous somites (PS-2 to PS-4). Cephalothorax tapering anteriorly (Fig. 1A), maximum width at level of retrostylets tip ( Table 2), dorsal eyespot, rostrum well-developed and protruded anteriorly, dorsal surface ornamented with bristles laterally, with paired dorsolateral stylets (= retrostylets) (Fig. 1B). Rostrum ornamented with paired bristles anteriorly, armed with rostral spine (Fig. 1D); rostral spine tapering posteriorly, extending up to one-third of cephalothorax length, with rounded tip (Fig. 1D). Retrostylets double (Fig. 1B) bearing medial spatulate processes, ornamented with bristles laterally; stylet curved, with acute tip; spatulate process rounded posteriorly. Free pedigerous somites decreasing gradually in width from anterior to posterior (Fig. 1A); PS-2 narrower than PS-1, with paired integumental windows laterally on tergite (Fig. 1C); PS-3 and PS-4, both lacking such integumental windows (Fig. 1A).

Urosome consisting of PS-5, genital double-somite, and 3 free abdominal somites (AS-1 to AS-3) ( Fig. 2B ); PS-5 ( Fig. 2B ) reduced, smaller and thinner than prosome somites, unornamented; genital double-somite ( Fig. 2B ), about 1.5 times wider than long, bearing paired slit-like genital apertures dorsally, ventral surface with paired pores near anterior margin and ornamented with spinules laterally; abdominal somites decreasing in width from anterior to posterior, each somite ornamented with spinules laterally ( Fig. 2B ); AS-3 (= anal somite) deeply incised posteriorly (= anus).

FIGURE 1. Gamispatulus schizodontis Thatcher & Boeger, 1984 —adult female. A body, ventral view. B retrostylets, dorsal view. C second pedigerous somite, dorsal view, with paired integumental windows laterally on tergite (arrowhead). D rostral spine, ventral view. A, C—Specimen INPA 2527a. B—Specimen INPA 2527b. D—Specimen INPA 2528a. Scale bars in µm.

Caudal rami ( Fig. 2B ), about 1.2 times longer than wide; each ramus ornamented with spinules on ventral surface and armed with 2 naked setae: seta 2 about 2 times longer than seta 1 ( Table 2).

Antennule 5-segmented ( Fig. 2D ), setal formula: 12, 4, 4, 2, 5 + 2 ae (total 29). Antenna ( Fig. 2C ) 4-segmented comprising coxobasis, and 3-segmented enp; coxobasis (= first segment) broad, with short naked seta; enp-1 (= second segment) ornamented with spinule row along outer margin and large spine near middle of inner margin; enp-2 (= third segment) slightly curved, unornamented; enp-3 (= fourth segment) reduced, unornamented; and 2 terminal claws (= inner and middle claw); middle claw curved, with fossa on concave margin (arrowed in Fig. 2C ); inner claw needle-shaped, thinner than middle claw, without fossa.

Buccal apparatus ( Fig. 3A ) comprising labrum, mandible, and maxilla; labrum broad, rounded posteriorly, partially covering other buccal components ( Fig. 3B ); mandible armed with 2 blades (anterior and posterior blade); both blades ornamented with spinules along posterior margin; maxilla 2-segmented, comprising syncoxa (= first segment) and basis (= second segment); syncoxa broad, with distal pore (arrowed in Fig. 3D ); basis with multiples spinules.

P1 to P4 biramous ( Figs. 4 A-C); each leg comprising coxa, basis, endopod (inner ramus) and exopod (outer ramus). P1 ( Fig. 4A ); coxa unornamented; basis with bare outer seta; enp 2-segmented, both segments ornamented with spinules and bristles on outer margin and lacking any ornament on inner margin; enp-1 (= proximal segment) armed with 1 plumose seta on inner margin; enp-2 (= distal segment) about 2 times longer than previous segment, armed with 2 serrated spines and 5 plumose setae; exp 3-segmented; exp-1 (= proximal segment) about 1.5 times longer than following segments, ornamented with spinules along outer margin and bristles on inner margin, armed with 2 unequal spines (= anterior and posterior spine) on outer margin; anterior spine short and triangular; posterior spine longer and thinner than previous spine, slightly curved; exp-2 (= middle segment) ornamented with two spinule rows on outer margin and lacking any ornament on inner margin; outermost spinules broad, scale-shaped; innermost spinules thinner and sharper than outermost spinules; armed with 1 plumose setae on inner margin; exp-3 (= distal segment) lacking any ornament on both margins, armed with 2 simple spines (not serrated) and 5 plumose setae.

P2 ( Fig. 4B ); coxa ornamented with 2 robust spinules; basis with bare outer seta; enp 3-segmented, all segments with spinules and bristles on outer margin and lacking any ornament on inner margin; enp-1 (= proximal segment) armed with 1 plumose setae on inner margin; enp-2 (= middle segment) armed with 2 plumose setae on inner margin; enp-3 (= distal segment) slightly smaller than previous segments, rounded, armed with 1 simple spine (not serrated) and 4 plumose setae; exp 3-segmented; exp-1 (= proximal segment) about 1.5 times longer than following segments, ornamented with 3 prominent spinules on outer margin and bristles on inner margin, armed with 1 simple spine (not serrated) on outer margin; exp-2 (= middle segment) ornamented with minute spinules on outer margin and lacking any ornamented on inner margin; spinules smaller than those present in exp-1; armed with 1 plumose seta on inner margin; exp-3 (= distal segment) ornamented with 2 set of minute spinules on outer margin, lacking any ornament on inner margin, armed with 6 plumose setae. P3 with same ornamentation and armament described for P2.

P4 ( Fig. 4C ); coxa ornamented with 5 robust spinules; basis with bare outer seta; enp 2-segmented; enp-1 (= proximal segment) with bristles along outer margin and lacking any ornament on inner margin, armed with 1 plumose seta on inner margin; enp-2 (= distal segment) ornamented with bristles (first half) and spines (second half) on outer margin, lacking any ornament on inner margin, armed with 4 plumose setae; exp 1-segmented; exopodal segment ornamented with prominent spinules on outer margin and bristles on inner margin; spinules slightly smaller than those present in P2 exp-1; armed with 2 minute spines and 4 plumose setae.

P5 reduced and represented by 2 naked setae ( Fig. 2B ). Spine and setal formula of biramous swimming legs is presented in Table 3.

Intercoxal sclerites slender, unornamented, with both ends directed posteriorly ( Fig. 2A ). Intercoxal plates of P1 and P2 both with paired pores laterally; intercoxal plate of P4, absent ( Fig. 2A ). Egg sac paired ( Fig. 4D ), uniseriate.

Remarks. The examined specimens of G. schizodontis agree in several respects with its original description by Thatcher & Boeger (1988a). This species can be readily distinguished from all other ergasilids, including species of closely related genera like Gamidactylus , Gamispinus , Pseudovaigamus , and Vaigamus (also known as “vaigamids”), in having the following combination of diagnostic features: (1) rostrum armed with rostral spine; (2) antennule 5-segmented; (3) antenna armed with 2 terminal claws (middle and inner claw); (4) cephalothorax armed with dorsolateral retrostylets bearing medial spatulate processes; and (5) P4 with enp 2-segmented and exp 1-segmented. The presence of retrostylets is a diagnostic feature present in all vaigamids, but the possession of spatulate processes has been found to be exclusive to G. schizodontis ( Thatcher & Boeger, 1984b) .

The specimens examined show minor differences in relation to the original description, as follows: (1) third antennary segment (= enp-2) unornamented (vs. with spine on inner margin); (2) antennule setal formula: 12, 4, 4, 2, 5 + 2 ae (vs. 10, 3, 4, 2, 8); and (3) general morphology of buccal apparatus — e.g., mandible with anterior blade lacking distal tooth (present in the original description). During the study of the attachment strategies in Ergasilidae, El-Rashidy (1999) did not report the antennary ornamentation described by Thatcher & Boeger (1988), in paratypes of G. schizodontis . These differences are not deemed sufficient to propose a new species based on these variations; they indicate the need for reassessment of the type material to have a more complete and accurate representation of these structures in G. schizodontis The present specimens represent the first report of G. schizodontis from S. intermedius as well as its second report of G. schizodontis in Southeast Brazil.

Figures

FIGURE 2. Gamispatulus schizodontis Thatcher & Boeger, 1984—adult female. A intercoxal sclerites and intercoxal plates, ventral view. B urosome, ventral view. C antenna, middle claw with fossa on concave margin (arrowhead). D antennule. Ae = aesthetascs. isI to isIV = first to fourth intercoxal sclerites. ipI to ipIII = first to third intercoxal plates. P5 = fifth leg. S1 = seta 1. S2 = seta 2. A, B, C—Specimen INPA 2527a. D—Specimen INPA 2529a. Scale bars in micrometers (µm).

FIGURE 3. Gamispatulus schizodontis Thatcher & Boeger, 1984—adult female. A buccal apparatus. B labrum. C mandible. D maxilla, syncoxa with pore (arrowhead). Ab = anterior blade. Pb = posterior blade. A, C, D, E—Specimen INPA 2529b. Scale bars in micrometers (µm).

FIGURE 4. Gamispatulus schizodontis Thatcher & Boeger, 1984—adult female. A leg 1. B leg 2 (= leg 3). C leg 4. D egg sac. A, C, D—Specimen INPA 2527a. E—Specimen INPA 2526. Scale bars in micrometers (µm).