Alienigena triangula

Cheng, Yu-Rong, Ho, Ming-Jay & Dai, Chang-Feng, 2016, Four anchimolgid copepods (Poecilostomatoida: Anchimolgidae) associated with the scleractinian coral Pavona explanulata (Lamarck, 1816) in Taiwan, Zootaxa 4174 (1), pp. 274-290 : 275-279

Alienigena triangula gen. et sp. nov.

( Figs 1–3 )

Type host. Pavona explanulata ( Lamarck, 1816) (family Agariciidae ).

Location in the host. Inside polyps.

Type locality. Yenliao Bay , northern Taiwan.

Etymology. The specific name triangula is an adjective based on the Latin “ triangulus ”, meaning triangular, and refers to the triangular form of cephalosome of the new species.

Type material. Nine females and five males obtained from washings of a coral colony collected at five m depth on 12 August 2010. The female holotype (NTUIO-COPE 1), male allotype (NTUIO-COPE 2), and paratypes (NTUIO-COPE s3; five females and three males) are deposited in the Institute of Oceanography , National Taiwan University, Taipei, Taiwan .

Description of female. Body ( Fig. 1 A–B) elongate. Body length of dissected specimen 0.88 mm (0.74–0.98 mm) and greatest width 0.13 mm (0.11–0.16 mm), based on five specimens. Segmentation of body distinct, but incomplete. Cephalosome ( Fig. 1 A–B) triangular, with prominent posterolateral expansions in dorsal view and fused to first pedigerous somite (leg 1). Urosome ( Fig. 1 C) 4-segmented. Genital double-somite ( Fig. 1 C) fused to fifth pedigerous somite, with genital apertures located dorsally. Abdomen ( Fig. 1 C) 3-segmented, first somite largest, third (anal) somite with prominent rounded anal operculum. Caudal ramus ( Fig. 1 C– D) small, armed with six naked setae. Surface of body without setules ( Fig. 1 A, B). Egg sacs not observed.

TABLE]. Poecilostomatoid copepods associated with scleractinian host corals of the genus Pavona .

Pavona cactus ( Forsskål, 1775) Madagascar Humes & Frost (1964) This species is not listed in the World Register of Marine Species (www.marinespecies.org/). Pavona venusta ( Dana, 1846) is currently regarded as a junior synonym of Pavona cactus ( Forsskål, 1775) . as Pavona praetorta ( Dana, 1846) .

Antennule ( Fig. 1 E) 7-segmented; armature: 4, 6, 5, 3, 4 + 1 aesthetasc, 2 + 1 aesthetasc, 7 + 1 aesthetasc. Antenna ( Fig. 1 F) 4-segmented; measurements (length × width) of segments 16 × 25 µm, 50 × 15 µm, 14 × 12 µm, 13 × 9 µm, respectively; armature: 1, 1, 3, and 1 terminal claw (63 µm long). Mandible ( Fig. 1 G) with prominent proximal notch; inner margin weakly bilobate with relatively small spinules; convex side with a large process and slender terminal lash. Maxillule ( Fig. 1 H) small, tipped with one short, smooth subapical seta and three plumose apical setae. Maxilla ( Fig. 1 I) 2-segmented, first segment stout and unarmed; second segment small, with distal lash bearing two spinules, one nodular tubercle halfway along concave margin of lash, one spiniform anterior seta, and one small proximal spinule. Maxilliped ( Fig. 1 J) 3-segmented, syncoxa largest, unarmed; basis with two unequal setae (larger one about 16 µm) along medial margin; endopod small, tipped with one larger pinnate process, one small subapical seta and one bipinnate spine.

Legs 1–4 ( Figs. 1 K, 2A–C) with 3-segmented exopods and 2-segmented endopods (except for leg 4 endopod being 1-segmented). Armature formula of spines (in Roman numerals) and setae (in Arabic numerals) as follows:

Coxa Basis Exopod Endopod Leg 1 0-0 1-0 I-0; I-0; IV+3 0-1; I+5 Leg 2 0-0 1-0 I-0; I-0; IV+3 0-1; III+2 Leg 3 0-0 1-0 I-0; I-0; IV 0-0; I

Leg 4 0-0 1-0 I-0; I-0; III I Leg 5 ( Fig. 2 D) reduced to two terminal setae and one adjacent dorsal (= outer basal) seta.

Leg 6 ( Fig. 1 E) represented by two small setae arising from operculum closing off genital aperture.

Description of male. Body ( Fig. 3 A–B) as in female but much more slender. Surface of body smooth. Body length of dissected specimen 0.87 mm (0.80–0.90 mm) and greatest width 0.10 mm (0.09-0.12 mm), based on five specimens. Urosome 5-segmented. Abdomen ( Fig. 3 A–B) 4-segmented, anal somite with rounded operculum as in female. Caudal ramus as in female, but much smaller.

Antennule, antenna, mandible, maxillule, and maxilla as in female except for antennule with three additional long aesthetascs (positions indicated by dots in Fig. 1 E). Maxilliped ( Fig. 3 C) consisting of three segments and terminal claw; first (syncoxa) and third (endopod) segment unarmed; second segment (basis) broadest, with two equal setae along medial margin and longitudinal rows of small spinules as indicated in Fig, 3C; terminal claw with one seta near the base.

Legs 1–4 as in female, without sexual dimorphism. Leg 5 ( Fig. 3 A, B, D) a small free segment with two setae and one adjacent dorsal (= outer basal) seta as in female.

Leg 6 ( Fig. 3 B, E) represented by two small setae on posteroventral operculum on genital somite.

Remarks. Members of the family Anchimolgidae are characterized by the derived form of the mandible, exhibiting a bilobed inner margin, and by the possession of a single terminal claw on the distal segment of the antenna ( Humes & Boxshall 1996; Boxshall & Halsey 2004). Based on these two characters, Alienigena triangula gen. et sp. nov. is here placed in the Anchimolgidae . Humes & Boxshall (1996) classified the 24 anchimolgid genera known at that time in five distinct generic groups characterized by the segmentation of the antenna and by the form and ornamentation of the armature of the maxilla, i.e. Amarda -group, Anchimolgus -group, Andrianellus - group, Odontomolgus -group and Schedomolgus -group. The Odontomolgus -group currently consists of four genera, Allopodion Humes, 1978 , Haplomolgus Humes & Ho, 1968 , Odontomolgus , and Kawanolus Humes, 1978 , all of which have a large process along the convex margin of the mandible ( Boxshall & Halsey 2004). The presence of a similarly large process along the convex margin of the mandible in Alienigena gen. nov. indicates a close relationship to the genera of the Odontomolgus -group. However, the elongate body shape of A. triangula gen. et sp. nov. is radically divergent from that in the other genera of this generic grouping and the armature formulae of legs 1–4 also seems to be unique among the currently known genera of the Anchimogidae. Hence, a new genus is proposed herein to accommodate this new form.

Figures

FIGURE 1. Alienigena triangula gen. et sp. nov. (female). A, habitus, dorsal; B, habitus, lateral; C, urosome; D, caudal ramus; E, antennule; F, antenna; G, mandible; H, maxillule; I, maxilla; J, maxilliped; K, leg 1. Scale bars: A – B = 0.2 mm; C = 0.1 mm; D – K = 0.02 mm.

FIGURE 2. Alienigena triangula gen. et sp. nov. (female). A, leg 2; B, leg 3; C, leg 4; D, leg 5; E, leg 6. Scale bars: A – E = 0.02 mm.

FIGURE 3. Alienigena triangula gen. et sp. nov. (male). A, habitus, dorsal; B, habitus, lateral; C, maxilliped; D, leg 5; E, leg 6. Scale bars: A – B = 0.2 mm; C – E = 0.02 mm.