Dactylopusioides malleus, Shimono & Iwasaki & Kawai, 2007

Shimono, Takaki, Iwasaki, Nozomu & Kawai, Hiroshi, 2007, A new species of Dactylopusioides (Copepoda: Harpacticoida: Thalestridae) infesting brown algae, and its life history, Zootaxa 1582 (1), pp. 59-68 : 60-65

publication ID	https://doi.org/ 10.11646/zootaxa.1582.1.6
publication LSID	lsid:zoobank.org:pub:FA31190B-61D6-4069-A844-6CB9B7C7CCCC
persistent identifier	https://treatment.plazi.org/id/03C5A67A-FFB4-FFE1-A2AF-F9EBFC37FE5B
treatment provided by	Felipe
scientific name	Dactylopusioides malleus
status	sp. nov.

Treatment

Dactylopusioides malleus sp. nov.

( Figs. 1–3 View FIGURE 1 View FIGURE 3 )

Type material. Holotype. Adult female (total body length 0.76 mm, measured from anterior margin of rostrum to the posterior margin of caudal rami) deposited in the Natural History Museum, London; registration no. NHM 2006. 1914.

Paratypes. 10 females and 5 males deposited in the Natural History Museum , London, registration no. NHM 2006. 1915-1929 . 10 females and 5 males deposited in the National Science Museum , Tokyo, Japan; registration numbers NMST-Cr 16855 and 15856. All type material was collected from the brown alga, Dictyota dichotoma in Oiso, Hyogo prefecture (34°33’N, 134°59’E) on 10 June 2002, by T. Shimono. Specimens have been preserved in 70% ethanol GoogleMaps .

FIGURE 2. Dactylopusioides malleus sp. nov., female. (A) P1; (B) P2; (C) P3; (D) P4; (E) P5. Scales: A–E, 0.05 mm.

Other material examined. 10 females and 6 males, dissected and mounted on slides in polyvinyl lactophenol, deposited in the personal collection of TS.

Diagnosis. Antennary exopod 1-segmented with 6 setae. Short, terminal seta on segment 2 of P2 endopod in male is plumose. Maxillule, coxa with 3 terminal setae. Male P5, baseoendopod and exopod with 3 and 5 setae, respectively. Male P6 reduced to a small plate with 2 setae.

Description of female. Mean total body length 0.74 mm (n=16), measured from anterior margin of rostrum to posterior margin of caudal rami. Color from greenish-brown to brownish-green. Body subcylindrical ( Fig. 1A View FIGURE 1 ). Rostrum ( Fig. 1B View FIGURE 1 ) articulated, triangular, apex rounded with 2 sensilla. Cephalothorax slightly shorter than wide. Genital double-somite divided dorsally and laterally by subcuticular rib. Genital field ( Fig. 1E View FIGURE 1 ) with copulatory pore situated medially. Anal somite with small, round anal operculum ( Fig. 1A View FIGURE 1 ). Caudal ramus ( Fig. 1F View FIGURE 1 ) shorter than wide; seta I longer than seta II; seta II spinous; seta III longer than seta II; seta IV one-third as long as seta V; seta VI slightly longer than VII; seta VII triarticulate. Egg-sac single.

Antennule ( Fig. 1C View FIGURE 1 ) short, 7-segmented. Two aesthetascs present, 1 on segment 3, the other on segment 8. Setal formula 1:9:13+a:2:4:4:7+a.

Antenna ( Fig. 1D View FIGURE 1 ) with small coxa unarmed, basis incompletely fused with first endopod segment forming allobasis, bearing long inner seta. Exopod short, 1-segmented with 3 long distal setae and 1 short and 2 long lateral setae. Endopod with 4 geniculate distal setae and 1 long and 1 short distal seta, and 2 short lateral setae.

Labrum ovoid, carved in anterior margin, equipped with denticles.

Mandibular gnathobase ( Fig. 1G View FIGURE 1 ) round, with long seta at inner corner. Basis large, with 1 seta. Endopod 1-segmented with 1 lateral and 4 terminal setae. Exopod 1-segmented with short seta and 5 long setae.

Maxillule ( Fig. 1H & I View FIGURE 1 ), arthrite of praecoxa with 4 stout spines and 3 spinulose setae around distal margin and 2 subapical surface setae. Coxa with 3 terminal setae. Basis with 6 setae. Endopod much smaller than exopod, with 2 setae. Exopod 1-segmented, with 3 setae on distal margin. Epipodite represented by a seta.

Maxilla ( Fig. 1J View FIGURE 1 ), syncoxa with 3 endites; proximal, middle and distal endites bearing 1 plumose, 1 plumose and 1 naked, and 2 naked setae, respectively. Allobasis represented by a thin elongate claw. Endopod absent.

Maxilliped ( Fig. 1K View FIGURE 1 ) pedestal. Syncoxa smooth and armed with 2 setae at inner corner. Basis with spinulose seta on inner-lateral margin. Endopod 1-segmented, prehensile with 2 spinulose setae.

P1 (Fig. 2A), coxa large. Intercoxal sclerite semi-oval, wider than long. Basis with stout spine at inner and outer distal corners. Endopod 3-segmented, prehensile; first segment elongated, longer than exopod, armed with long spinulose seta in proximal half of inner margin; second segment asetose, small; third segment short, armed with 2 serrate claws and inner, short, spinulose seta. Exopod 3-segmented; first segment with outer spine; second segment bearing outer spine and inner seta distally; third segment shortest, bearing 4 terminal spines increasing in length towards medial edge.

P2–P4 (Fig. 2B–D) coxa rectangular. Intercoxal sclerite longer than wide. Basis with outer seta. Rami 3- segmented, with copious spinules on outer margin, endopod shorter than exopod. Setal formula as follows:

Exopod Endopod

P2 1: 1: 2.2.3 1: 2: 2.2.1

P3 1: 1: 3.2.3 1: 2: 3.2.1

P4 1: 1: 3.2.3 1: 2: 2.2.1

P5 (Fig. 2E), endopodal lobe exceeding exopod slightly, baseoendopod with 5 setae on distal and subdistal, basal seta naked and second innermost seta shortest, exopod bearing 5 setae.

P6 ( Fig. 1E View FIGURE 1 ) close to genital pores, trapezoidal, inner seta inwardly directed.

Male. Mean total length 0.62 mm (n=10). Differs from the female in the following respects:

Antennule ( Fig. 3A View FIGURE 3 ) haplocer, 9-segmented, an aesthetasc on segment 3, segment 5 and segment 9.

P1 ( Fig. 3B & C View FIGURE 3 ), intercoxal sclerite not oval. Inner spine on basis stout, hammer-shaped.

P2 ( Fig. 3D View FIGURE 3 ) endopod modified, 2-segmented; outer spine on segment 2 shorter and stouter than that of

female; outer terminal plumose spine on segment 2 much smaller than that of female. Setal formula as follows:

Exopod Endopod

P2 1: 1: 2.2.3 1: 2.2.2

P5 ( Fig. 3E View FIGURE 3 ), right and left baseoendopods fused medially, bearing 3 serrate spiniform setae on endopodal lobe and a naked seta at outer corner. Exopod bearing 5 spinulose setae.

P6 ( Fig. 3F View FIGURE 3 ) reduced to small plate with 2 setae.

Etymology. The epithet malleus refers to the stout hammer-shaped inner spine on the basis of P 1 in the male; different compared to known species of Dactylopusioides .

Life history. In the field, Dactylopusioides malleus sp. nov. ( Fig. 4A View FIGURE 4 ) was found forming burrows in the thalli of dictyotalean brown algae Dictyota dichotoma , Dictyota maxima and Dictyopteris undulata . At Imagoura, Maiko, Oiso and Yura, in Hyogo Prefecture (central Honshu), the new species was found from May to August in the intertidal and subtidal zones. All life history stages of the new species were found burrowing into the thalli of Dictyopteris undulata at Imagoura and Dictyota dichotoma at Yura, on 17 June 2003 and on 13 July 2000, respectively.

In laboratory experiments, D. malleus sp. nov. progressed through its complete life cycle (from egg to adult to egg) while eating only the tissue of D. dichotoma , which was its host in the field. Eggs hatched out in 3–4 (3.6 ± 0.5 S.D.) days. The first stage of the nauplii made burrows (tunnels) by eating the host algal tissue from the surface, and then entering the algal tissue. In the burrows, nauplii ate the algal cells but left the outer cell wall and overlying cuticle of the peripheral cells intact ( Fig. 4B View FIGURE 4 ); thus the burrow was not exposed to out- side. Nauplii molted several times within the burrow and then formed a gelatinous matrix, within which they metamorphosed ( Fig. 4C View FIGURE 4 ). The copepodids left the burrow and continued development on the surface of the algal tissue, inside a capsule made of mucus they secreted ( Fig. 4D–F View FIGURE 4 ). At 18 °C, copepodids became adults in 9–13 (11.2 ± 1.5) days. Both nauplii and copepodids occasionally left the burrow or capsules and formed new burrows or capsules. At 18 °C, adult females changed capsules at intervals of 2.2 ± 1.2 days. No mating behavior was observed during the experiments, but eventually the females bore eggs in an egg sac, in an experimental setting where both males and females were present. In contrast, females did not form eggs in the absence of males. Females produced eggs at intervals of 4.3 ± 1.2 days, and retained the egg sac until the eggs hatched. At 18 °C, each egg sac contained 7–24 (17.1 ± 4.1) eggs.