Anchimolgus latens Humes 1978

Anchimolgus latens

TYPE MATERIAL.—9 , 11 from one Fungia (Ctenactis) echinata (Pallas), in 3 m, southwestern side of Goenoeng Api, Banda Islands, 4°31′45″S, 129°51′55″E, 25 May 1975. Holotype , allotype, and 15 paratypes (7 , 9 ) deposited in the National Museum of Natural History, Smithsonian Institution, Washington, D.C.; the remaining paratypes (dissected) in the collection of the author.

OTHER SPECIMENS.—From Fungia echinata: 1 , 1 from one host, in 5 m, Poelau Gomumu, south of Obi, Moluccas, 1°50′00″S, 127°30′54″E, 30 May 1975.

From Fungia (Fungia) fungites (Linnaeus): 13 , 43 from 11 hosts, in 3 m, Natsepa, Ambon, 3°37′05″S, 128°17′00″E, 24 April 1975.

From Fungia (Pleuractis) paumotuensis Stutchbury: 1 , 3 from 2 hosts, in 2 m, Poelau Naira, Banda Islands, 4°31′45″S, 129°53′35″E, 2 May 1975.

From Herpolitha limax (Esper): 13 , 43 from one host, in 2 m, Poelau Naira, Banda Islands, 4°31′45″S, 129°53′35″E, 8 May 1975.

FEMALE.—Body (Figure 4a) with prosome slender and moderately thickened dorsoventrally. Length 1.52 mm (1.43–1.68 mm) and greatest width 0.49 mm (0.45–0.55 mm), based on 9 specimens. Epimera of segment of leg 1 inconspicuous, those of segment of leg 2 pointed posteriorly, those of segment of leg 3 truncated, and those of small segment of leg 4 rounded. Ratio of length to width of prosome 1.85:1. Ratio of length of prosome to that of urosome 1.57:1.

Segment of leg 5 (Figure 4b) 91 × 228. Genital segment 260 long, 194 in greatest width, and 118 in least width. Anterior two-thirds of segment expanded with slightly undulating margins in dorsal view. Genital areas located dorsolaterally just in front of middle of segment. Each area (Figure 4c) with two small naked setae about 20 and a small spiniform process. Postgenital segments from anterior 101 × 101, 81 × 91, and 86 × 96. Posteroventral margin of anal segment with row of minute spinules on both sides.

Caudal ramus (Figure 4d) elongated, 135 × 45, with ratio of 3:1. Outer lateral seta 125, dorsal seta 65, outermost terminal seta 154, innermost terminal seta 200, and two long median terminal setae 231 (outer) and 308 (inner), both inserted between smooth dorsal flange and ventral flange with minute marginal spinules. All setae with long dense lateral hairs except dorsal seta, which is naked.

Body surface with a few hairs (sensilla) as in Figure 4a.

Egg sac (Figure 4e) oval, variable in length, approximately 385–460 × 200, containing 12–13 irregular eggs with diameter 104–117.

Rostrum (Figure 4f) in ventral view with weakly defined posteroventral edge; in lateral view (Figure 4g) projecting triangularly. First antenna (Figure 4h) 465 long. Lengths of seven segments: 29 (63 along anterior margin), 138, 33, 99, 68, 45, and 19 respectively. Setation as in Anchimolgus notatus. Longest seta on first segment noticeably stouter than other antennal setae. All setae naked.

Second antenna (Figure 4i) 385 long. Formula for armature as in A. notatus, but minute setae on first two segments hyaline and obscure. Second segment with small slender spinules on inner surface. Fourth segment 63 along outer side, 45 along inner side, and 13 wide. Claw 36 along axis.

Labrum (Figure 4j) with two broad posteroventral lobes. Mandible (Figure 4k) and paragnath (Figure 4j) resembling those of A. notatus. First maxilla (Figure 4l) with four setae. Second maxilla (Figure 5a) similar to that of A. notatus, but spinules on inner seta on second segment much longer on inner side than on outer side. First spine on lash stouter and less pointed than succeeding spines. First segment lacking fine ornamentation. Maxilliped (Figure 5b) much like that of A. notatus, but pointed tip with a few spinules on both sides.

Ventral area between maxillipeds and first pair of legs as in A. notatus.

Legs 1–4 (Figure 5c–f) segmented and armed as in A. notatus. Third segment of endopod of legs 2 and 3 with outer spine shorter than inner terminal spine. Leg 4 with small naked coxal seta 15 long. Exopod 213. First segment of endopod 44 long including spiniform processes (39 without these processes) and 34 wide, its inner distal plumose seta 78. Second segment 68 with spiniform processes (65 without processes) and 24 in greatest width (18 in least width); two terminal fringed spines 39 (outer) and 70 (inner). Outer margin of both segments with hairs.

Leg 5 (Figure 5g) with long free segment 135, its greatest width at slight inner proximal expansion 34, its least width distally 26. Two terminal naked setae 81 and 60. Segment ornamented with small spines along outer surface. Dorsal seta 80 and naked.

Leg 6 represented by two setae on genital area (Figure 4c).

Living specimens in transmitted light colored as in A. notatus.

MALE.—Body (Figure 6a) with prosome a little less slender than in female. Length 1.28 mm (1.22–1.35 mm) and greatest width 0.39 mm (0.37–0.41 mm), based on 10 specimens. Ratio of length to width of prosome 1.57:1. Ratio of length of prosome to that of urosome 1.08:1.

Segment of leg 5 (Figure 6b) 52 × 138. Genital segment 286 × 221, longer than wide. Four postgenital segments from anterior to posterior 49 × 73, 49 × 70, 36 × 68, and 52 × 73.

Caudal ramus resembling that of female but smaller, 94 × 39, with ratio of 2.41:1.

Rostrum as in female. First antenna similar to that of female, but three long aesthetes added as in A. notatus (at points indicated by round dots in Figure 4h). Formula as in male of A. notatus.

Second antenna (Figure 6c) resembling that of female but inner surfaces of second and third segments with small spines.

Labrum, mandible, paragnath, first maxilla, and second maxilla like those of female. Maxilliped (Figure 6d) with first segment unarmed. Second segment with two slender naked setae and row of spines. Small third segment unarmed. Claw 265 along axis (including terminal lamella) and bearing two unequal proximal setae, longer seta jointed and finely barbed distally along one side.

Ventral area between maxillipeds and first pair of legs similar to that in female.

Leg 1 with endopod formula 0–1; 0–1; II, 4 (Figure 6e) but in other respects like that of female. Legs 2–4 like those of female.

Leg 5 (Figure 6f) with free segment 42 × 13, without proximal inner expansion. Two terminal setae 20 (inner) and 38 (outer).

Leg 6 (Figure 6g) a posteroventral flap on genital segment bearing two naked setae about 31.

Spermatophore not observed.

Living specimens colored as in female.

ETYMOLOGY.—The specific name latens (Latin, = hidden or sheltered) refers to the concealment of the copepods on the host.

COMPARISON WITH OTHER SPECIES OF Anchimolgus.—The shape of the genital segment in the female distinguishes Anchimolgus latens from all other species in the genus. The slightly enlarged seta on the first segment of the first antenna may be used as a recognition character in separating the new species from all but Anchimolgus tener Humes, 1973. This character, however, requires a keen eye and a certain amount of practice before it can be used successfully. The new species can best be separated from other species in the genus by use of the key provided below.

Anchimolgus latens is anatomically similar to A. notatus in certain respects, but differs in details such as the length of the caudal ramus, the slender third and fourth segments of the second antenna, the relative lengths of the spines on the third segment of the endopod of legs 2 and 3, the lengths of the terminal spines on the endopod of leg 4, and the nature of leg 5 in the female.

Moluccas; New Caledonia