Tiddergasilus iheringi ( Tidd, 1942 ) Marques & Boeger, 2018

Marques, Taísa Mendes & Boeger, Walter A., 2018, Proposal of Tiddergasilus gen. nov. (Ergasilidae: Cyclopoida) for T. iheringi comb. nov. from the gills of Hoplias malabaricus (Erythrinidae: Characiformes) from Brazil, Zoologia (e 21577) 35, pp. 1-6 : 2-5

Tiddergasilus iheringi ( Tidd, 1942) , comb. nov.

Figs 1–10

Type host. Hoplias malabaricus (Bloch, 1974)

Site on host. Gill filaments.

Type locality. Campina Grande , Paraíba, Brazil .

Male. Unknown

Type specimens. Holotype and Paratype in USNM Catalog #79255 .

Redescription (based on 9 females). Body comprising prosome and urosome; prosome consisting of non-inflated cephalosome, rostrum broad and well defined. Cephalosome well defined. Cephalosome and first pedigerous somite partially fused, followed by three free pedigerous somites. Cephalothorax length less than twice width, more than half body length. Antennule 6-segmented, tapering distally, with 23 setae, aesthetascs not observed. Antenna small and robust, with coxobasis, 2-segmented endopod, and terminal claw. Coxobasis short, with small seta at inner distal corner, membrane between coxobasis and first endopodal segment not inflated; first endopodal segment lacking spinules on internal margin, submedian sensillum present, lacking cuticular elevation;second segment (approximately trhee times shorter than first), lacking sensillum; claw with unique morphology (short, recurved with sub-proximal indentation in inner margin). Maxillule not observed; mandible with middle and posterior blades, anterior blade absent, middle blade toothed along posterior edge. Maxilla lacking spinulate seta; basis partially toothed on convex margin. Swimming legs 1–4 biramous each with 2-segmented protopod comprising coxa and basis. Interpodal plates of all legs with two rows of spinules ventrally. The armature of legs (spines, Roman numerals; setae, Arabic numerals) as follows:

Leg 1. Coxa with smooth margins, lacking spinules; basis with spinules and outer seta. Exopod 2-segmented; first segment non-pilose, with spinules distally on outer margin, and a spinulate distal spine; second segment lacking spinules and distal spine, with single seta; third segment lacking spinules, lacking pectinate seta, with four pilose setae and one spinulate seta, plus two distal spinulate spines. Endopod 2-segmented; first segment with spinules distally on outer margin, pilose, with single seta; second segment with spinules on outer margin, with five setae, plus 2 spinulated spines, one long, one short. Leg 2. Coxa lacking spinules; basis lacking spinules, with outer seta. Exopod 3-segmented; first segment non-pilose, with spinules on outer margin and non-spinulate distal spine, lacking seta; second segment non-pilose, lacking spinules, with single seta; third segment with spinules distally on outer margin, with six setae, plus non-spinulated distal spine. Endopod 3-segmented; first segment non-pilose, with spinules on outer margin and with single seta; second segment non-pilose, with spinules on outer margin, with single seta, distal spine absent; third segment with 4 setae and spinules immediately anterior to setae, plus non-spinulated distal spine. Leg 3. Coxa lacking spinules; basis lacking spinules, with outer seta. Exopod 3-segmented; first segment non-pilose, with spinules on outer margin and non-spinulate distal spine, lacking seta; second segment non-pilose, lacking spinules, with single seta, distal spine absent; third segment with spinules distally on outer margin, with six setae, plus non-spinulate distal spine. Endopod 3-segmented; first segment non-pilose, with spinules on outer margin and with single seta; second segment non-pilose, with spinules on outer margin, with single seta, distal spine absent; third segment with 4 setae and spinules immediately anterior to setae, plus non-spinulate distal spine. Leg 4. Coxa lacking spinules; basis with outer seta, lacking spinules. Exopod 2-segmented; first segment non-pilose, lacking spinules and seta, distal spine absent; second segment with spinules on outer margin, with 4 setae, plus non-spinulate distal spine. Endopod 2-segmented; first segment non-pilose, with spinules on outer margin, with single seta; second segment with spinules distally on outer margin, with 4 setae, distal spine absent. Leg V reduced to single seta.

Urosome consisting of fifth somite, genitaldouble-somite, and three free abdominal somites. Genital double-somite barrelshaped narrowing posteriorly, ventral surface lacking spinules. Abdominal somites with a row of spinules on posteroventral margins; third abdominal somite bipartite. Caudal rami as long as wide, each armed with one long, one medium and two smaller (lateral and ventral) setae, rows of spinules present ventrally, immediately anterior to smaller setae. Egg sac many times longer than wide, composed of 2–3 rows of eggs.

Phylogeny

An initial hypothesis of the evolutionary relationships of Ergasilidae genera was constructed manually using Hennigian Argumentation ( Hennig 1966, Wiley 1981). The topology of the resulting cladogram was tested with PAUP* to confirm that it was one of the most-parsimonious trees. This hypothesis is presented in Figure 11 (tree length 28; C.I. = 0.68 and R.I. = 0.76) – it is one of 15 equally parsimonious trees obtained with PAUP*. Bremer Support is presented in gray numbers on each respective node.

Three main clades were observed within the Neotropical Ergasilidae . One is comprised of the three outgroup genera: Acusicola Cressey, 1970 , Miracetyma Malta, 1993 and Amplexibranchius Thatcher & Paredes, 1985 . Another clade is composed of Gamidactylus Thatcher & Boeger, 1984 , Gamispatulus Thatcher & Boeger, 1984 , Pseudovaigamus Amado, Ho & Rocha, 1995 , Vaigamus Thatcher & Robertson, 1984 and Gamispinus Thatcher & Boeger, 1984 , which represents members of the clade formerly referred to as the Vaigamidae . Although this clade corroborates the results of past morphological analyses ( Amado et al. 1995, Tang and Kalman 2008), the relationships between the included genera differ.

The same is true for Acusicola , Amplexibranchius and Miracetyma . As in the previous phylogenies ( Amado et al. 1995, Tang and Kalman 2008), those genera are sister taxa, but their relative phylogenetic relationships differ in the present analysis, with the sister-group Amplexibranchius and Miracetyma supported the following synapomorphies: second endopod segment of leg 1 modified (Character 9), endopod of leg 1 lacking spines, and endopod of leg 2 lacking spines (Characters 10 and 12). Accordingly, this is the most robust clade in the phylogeny, presenting the highest Bremer support.

Tiddergasilus gen. nov. is a putative sister taxon of Neotropical species of Ergasilus . The two genera share antennule with 6-segments (Character 3). The hypothetical ancestor of this group of Ergasilus and Tiddergasilus gen. nov. forms a polytomy with Gauchergasilus Montu & Boxshall, 2002 and Prehendorastrus Boeger & Thatcher, 1990 . Removal of the highly homoplastic character 3 from the analysis results in a polytomy with the clade of genera of the former Vaigamidae , Ergasilus , and the clade Rhinergasilus + Brasergasilus + Pindapixara ( Fig. 12, treelength 24; C.I. = 0.70 and R.I. = 0.76).

Five homoplasious character states were observed: (1) antennule 6-segmented in Ergasilus + Tiddergasilus , Vaigamus , and Brasergasilus + Pindapixara (Character 3); (2) second segment of antenna reduced in Brasergasilus + Pindapixara + Rhinergasilus and Tiddergasilus (Character 5); (3) spines on second endopod absent in Amplexibranchius + Miracetyma and Rhinergasilus (Character 10); (4) leg 4 absent in Rhinergasilus and Brasergasilus (Character 13). (5) leg 4 endopod 2-segmented in Brasergasilus + Pindapixara + Rhinergasilus + Gamidactylus + Gamispatulus + Vaigamus + Gamispinus and Tiddergasilus (Character 15).

The analysis also shows four reversals: loss of rostral spine in Gamidactylus (Character 1); spines on exopod 2 absent in Pindapixara (Character 11); leg 4 with exopod 2-segmented and endopod 3-segmented in Pseudovaigamus (Characters 14 and 15).