Hamaticyclops ahni is described as a new genus and species from the Californian shore of the United States. It was discovered as a victim of the sea anemone Anthopleura elegantissima (Brandt). The new genus is closely related to the genus Hemicyclops but possesses, as significant autapomorphies, three strong claws on the second endopodal segment of antenna and a markedly elongate exopod of leg 5 with its protopod fused to somite.
Copepods of the family Clausidiidae Embleton, 1901 are generally known to be the most primitive among poecilostome cyclopoids. They live in association with various marine invertebrates, such as cnidarians, polychaetes, mollusks, and crustaceans, but many species have been found free.
During a field survey done in 2002 along the seashore of California, United States, I tried to collect some copepods associated with intertidal sea anemones. On the shore of Santa Barbara I sucked material in the gastrovascular cavity of sea anemones for copepods using a large pipette. Most of copepods collected in this way turned out to be species of the genus
The exoskeleton of the single copepod specimen was collected from the gastrovascular cavity of the sea anemone
Order Poecilostomatoida Burmeister, 1835
Family Clausidiidae Embleton, 1901
Diagnosis. Female: Body cyclopiform. Prosome consisting of cephalothorax and 3 free metasomites. Urosome 5-segmented. Antennule 7-segmented, with 5 setae on first segment. Antenna consisting of basis and 3-segmented endopod; second endopodal segment with 3 strong claws and 1 seta; third endopodal segment originated from outer side of second segment, with 4 claws and 3 setae. Mandible with 4 distal elements. Paragnath a lobe covered by spinules and setules. Maxilla 2-segmented, with 2 spiniform setae on proximal segment and 1 large process and 3 spiniform elements on distal segment. Maxilliped 4-segmented, with 2 large setae on first and second segment and 5 elements on terminal segment. Legs 1-4 with 3-segmented rami. Spines and setae on third exopodal segments of legs 1-4: 8, 9, 9, and 9, respectively; those on third endopodal segments of legs 1-4: 5, 6, 6, and 5, respectively. Leg 5 represented by 1 dorsolateral seta on fifth pedigerous somite and free exopod; protopod completely fused to somite; exopod elongated, extending over posterior margin of genital double-somite and directed backwards, with 4 distal setae.
Type species.
Etymology. The generic name is the combination of
Material examined. One ♀ (holotype, without antenna and legs 1 and 2 of right side) from the gastrovascular cavity of the sea anemone
Description. Female: Body (Fig. 1A) relatively large, 2.59 mm long, excluding caudal setae. Prosome moderately broad, 1.02 mm long, distinctly shorter than urosome, with nearly parallel lateral margins. Greatest width of prosome 876 μm across posterior region of cephalothorax. Cephalothorax with roundly convex anterior margin and concave posterodorsal margin. First and second pedigerous somites with excavated posterodorsal margin. Third pedigerous somite slightly narrower than preceding somite.
Urosome T-shaped and 5-segmented. Fifth pedigerous somite (=first urosomite) 792 μm wide, characteristically wider than fourth pedigerous somite. Genital double-somite 454×427 μm, much narrower than fifth pedigerous somite, with slight lateral constriction and paired dorsolateral notches in middle; genital area located on sides of weak anterolateral expandion. Three free abdominal somites 208×347, 208×338, and 154×292 μm, respectively. Anal somite with fine spinules along posteroventral margin. Caudal rami divergent; each ramus 362×131 μm (ratio 2.76 : 1) and evenly tapering, with 6 setae; outer lateral seta located subdistally, other 5 setae located distally.
Rostrum short and strongly tapering (Fig. 1B). Antennule (Fig. 1C) shorter than cephalothorax and 7-segmented, with armature formula 5, 15, 6, 4, 4+aesthetasc, 2+aesthetasc, and 7+aesthetasc; aesthetasc on fifth segment very thin; pinnate setae: 1 on second, fourth and sixth segments each, 2 on fifth, and 3 on terminal segments. Antenna (Fig. 1D) consisting of basis and 3-segmented endopod; basis with 1 mediodistal seta; first endopodal segment with 1 medial seta at place slightly distal to midlength of medial margin; second endopodal segment armed with 1 seta and with 3 strong claws on distinctly produced mediodistal corner (Fig. 1D, E); third endopodal segment slightly longer than wide, originating from outer side of second segment and armed with 3 setae and 4 spiniform claws.
Labrum (Fig. 1F) 163 μm wide, with spinules on lateral and posterior margins and patches of spinules mid-posterior area of ventral surface; posterior margin slightly concave. Mandible (Fig. 1G) distally armed with 1 claw-like, massive ventral element, 1 spinulated, plate-like element, and 2 spinulated dorsal setae. Paragnath (Fig. 1H) as lobe covered with spinules and setules. Maxillule (Fig. 2A) ditally bilobed, with 3 setae on narrower lobe and 5 setae on broader lobe. Maxilla (Fig. 2B) 2-segmented; proximal segment with 2 spiniferous spines, larger one of them with small subsidiary seta proximally; distal segment armed with 3 spiniferous spines and 1 large process bearing 4 cusps on one side. Maxilliped (Fig. 2C) 4-segmented; first segment with 2 setae, one of them spiniform and bearing several stiff setules; second segment with 2 spiniform setae bearing stiff setules on medio-proximal projection and longitudinal row of fine setules along medial margin; third segment short and unarmed; fourth segment armed with 5 elements: 1 large, gently curved claw (218 μm long), 1 process-like, spinule-bearing spine (117 μm long), and 3 slender, naked setae, one of latters enlarged, about 280 μm long.
Legs 1-4 (Figs. 2D, E, 3A, B) with 3-segmented rami. Endopod of legs 1 and 2 distinctly longer than their exopod. Inner seta on coxa of legs 1-3 pinnate, but that of leg 4 naked. Posterior margin of intercoxal sclerite of leg 1 with setules but those of legs 2-4 with spinules. Outer spines on exopod of leg 1 with subapical setule. Armature formula of legs 1-4 as follows:
Leg 5 consisting of 1 dorsolateral seta on fifth pedigerous somite and 1-segmented free exopod (Fig. 1A), with original protopod completely fused to somite; exopod (Fig. 2F) characteristically elongated, rod-shaped, gradually narrowing distally, 708×119 μm (ratio 5.95 : 1), directed posteriorly, extending to midway of first free abdominal somite, and armed distally with 4 greatly unequal naked setae and oblique rows of fine spinules. Leg 6 not seen.
Male: Unknown.
Etymology. The specific name ahni is named after the entomologist Dr. Kee-Jeong Ahn, Department of Biology, Chungnam National University, who introduced the author to the trip to the Californian shore in 2002.
Boxshall and Halsey (2004) recognized seven genera as valid in the Clausidiidae:
Boxshall and Halsey (2004) removed
The most characteristic features of
Another characteristic feature of
In summary,