Ho Young Soh

Evolutionary switching from suspension feeding to carnivory in the calanoid family Heterorhabdidae (Copepoda)

ABSTRACT Light and electron microscopy revealed the fine structure of the feeding appendages and labrum of the deep-sea calanoid family Heterorhabdidae. The family accommodates 7 genera, ranging from typical suspension-feeders, Disseta and Microdisseta, to typical carnivores, Hemirhabdus, Heterorhabdus, and Neorhabdus. Heterostylites and Mesorhabdus are intermediate between these two feeding modes. The most remarkable transformation among these genera occurs in the mandible, maxilla, and labrum. The suspension-feeders and the intermediate types exhibit no extreme specialization in these structures, but the carnivores carry a lateral pair of large gland openings on the posterior surface of the labrum, from which a secretion is presumably injected into either a groove or a tubular lumen of the ventralmost tooth of the mandible. The substance is supposedly released into the prey from a hypodermic needlelike tip of the tooth. In these carnivores some setae on the basis and the first endopod segment of the maxilla are highly modified into a grasping organ. The elongation of the maxillary praecoxa is found only in the carnivore Heterorhabdus and the intermediate Heterostylites. The large gland openings of the labrum in the carnivores presumably have been converted from normal ones in the suspension-feeders. This drastic evolutionary switching from suspension feeding to carnivory in the family appears to have been accomplished only by the following factors: (1) reduction and/or loss of elements, including mandibular teeth; (2) specialization (e.g., sclerotization) of elements; (3) elongation of segments; and (4) conversion of labral gland system. Cladistic analysis provisionally indicates that the first offshoot is the suspension-feeder Disseta and that the elaborate carnivores using venom represent the evolutionarily derived terminal branch of the family.

Three new species of the demersal calanoid copepod Placocalanus (Ridgewayiidae) from Okinawa, Southern Japan

Abstract Three new species of Placocalanus are described from sandy bottoms off Nagannu Island, Okinawa, southern Japan, at a depth of ca 50 m. This is the first record of the genus in the Indo-Pacific region. A number of differences in segmentation and setation in appendages are found between the Pacific and Atlantic species. In particular the Pacific species have a reduced number of setae of the legs compared with their Atlantic congeners. Specialized characters of Placocalanus such as the laterally compressed prosome, expanded proximal plate of the antennule and markedly modified leg 1 are discussed from a functional point of view. Cooccurrence of several species of a genus is common among demersal calanoid copepods, and is briefly discussed.

The caligid life cycle: new evidence from Lepeophtheirus elegans reconciles the cycles of Caligus and Lepeophtheirus (Copepoda: Caligidae).

The developmental stages of the sea louse Lepeophtheirus elegans (Copepoda: Caligidae) are described from material collected from marine ranched Korean rockfish, Sebastes schlegelii. In L. elegans, setal number on the proximal segment of the antennule increases from 3 in the copepodid to 27 in the adult. Using the number of setae as a stage marker supports the inference that the post-naupliar phase of the life cycle comprises six stages: copepodid, chalimus I, chalimus II, pre-adult I, pre-adult II, and the adult. We observed variation in body length in both of the chalimus stages which we consider represents an early expression of sexual size dimorphism. We interpret the larger specimens of chalimus I as putative females, and the smaller as putative males; similarly with chalimus II, larger specimens are putative females and the smaller are males. Two patterns of life cycle are currently recognized within the Caligidae but the evidence presented here reconciles the two. We conclude that the typical caligid life cycle comprises only eight stages: two naupliar, one copepodid, and four chalimus stages preceding the adult in Caligus, but with the four chalimus stages represented by two chalimus and two pre-adult stages in Lepeophtheirus. This is a profound change with significant implications for the aquaculture industry, given that lice monitoring protocols include counts of chalimus stages and use temperature to predict when they will moult into the more pathogenic, mobile pre-adults. Lice management strategies must be tailored to the precise life cycle of the parasite.

Caligus sclerotinosus (Copepoda: Caligidae), a serious pest of cultured red seabream Pagrus major (Sparidae) in Korea

Caligid copepods (Crustacea) known as sea lice are pests of cultured fish, causing serious diseases and economic losses in fish aquaculture worldwide. One species, Caligus sclerotinosus Roubal, Armitage & Rohde, 1983 (Caligidae), is considered a serious pest of the highly prized red seabream Pagrus major (Temminck and Schlegel, 1843) (Sparidae) cultured in Japan. Recently, in neighboring Korea, red seabream culture has intensified and almost replaced yellow tail culture. However, until now, there have been no reports on infection of this sea louse from red seabream in Korea. We surveyed 120 (20 fish per month) P. major from a sea ranched Tongyeong Marine Research Center aquaculture facility, Gyeongsangnamdo, Korea for six months in 2011 (June to November). We recorded severe infection by the sea louse C. sclerotinosus on the skin of P. major. Prevalence was 100%, mean intensity 7.06, maximum intensity 49, and minimum intensity 2. Adult females (624), males (219) and few chalimi (5) were observed and identified by their morphology. As an average of all our collections, less than 0.6% of individuals were chalimi. We suggest, therefore, that adults of C. sclerotinosus undergo ontogenetic host switching after their final moult. No infection of C. sclerotinosus was found on wild P. major collected from Tongyeong and Yeosu fish markets on the southern coast of Korea. Severe infection by this sea louse may cause secondary infections of the host. This copepod is already reported from Australia and Japan and hence, this is the first report from Korea. We expect this pest to have an impact on Korean red seabream fisheries equally serious to that being experienced in Japan.

Genetic Identification and Molecular Phylogeny of Pseudodiaptomus Species (Calanoida, Pseudodiaptomidae) in Korean Waters

Abstract Five species of the genus Pseudodiaptomus, P. inopinus, P. poplesia, P. marinus, P. nihonkaiensis, and P. sp. occur in Korea nearshore waters. Although the four species except for P. sp. have been classified into Lobus and Ramosus groups, two for each group, based on morphological characters, this classification had yet to be confirmed by molecular characters. Here, we determined molecular characters and phylogenetic relationships of the five species in order to evaluate the morphology-based groupings and the species identifications. For this, a 625-bp DNA region of the mitochondrial gene cytochrome oxidase subunit I (mtCOI) was sequenced and compared among the species. Intraspecific variation of the sequences is less than 0.6%, while interspecific variation ranges from 17.6–26.7%, indicating every species, including P. sp., is a genetically distinct, valid species. Phylogenetic trees of the mtCOI DNA reveal that the Lobus-group species including P. inopinus and P. poplesia form a well-supported clade and that P. sp. belongs to this group. On the other hand, the Ramosus group clade consisting of P. marinus and P. nihonkaiensis is not well supported by bootstrap analyses, suggesting that further evaluation of the validity of this group assignment is needed.

The first record of two demersal calanoid copepods, Pseudodiaptomus poplesia and P. nihonkaiensis in Korea, with remarks on morphology of the genital area

The demersal calanoid copepods Pseudodiaptomus nihonkaiensis Hirakawa, 1983 and P. poplesia (Shen, 1955) are redescribed from Korean waters. Using scanning electron microscopy, we examine the morphology of the female genital systems of four species of Pseudodiaptomus (P. inopinus, P. marinus, P. nihonkaiensis and P. poplesia), revealing interspecific differences. The zoogeography of these four species is discussed.

Redescription of two Pennellids (Copepoda, Siphonostomatoida) from Korea with a key to species of Peniculus von Nordmann, 1832

Abstract Redescriptions of two pennellid copepods, Peniculus minuticaudae Shiino, 1956 and Peniculus truncatus Shiino, 1956, are provided, based on postmetamorphic adult females collected from marine ranched fishes captured at Tongyeong marine living resources research & conservation center, Korea. Peniculus minuticaudae was collected from the soft fin rays of black scraper Thamnaconus modestus. It can be distinguished from the other two closely related congeners Peniculus ostraciontis Yamaguti, 1939 and Peniculus truncatus by having a well developed triangular-shaped abdomen; the abdomen is rudimentary in other two species. This is thefirst report of the occurrence of Peniculus minuticaudae in Korea. Peniculus truncatus was collected from the dorsal fin of Korean rockfish Sebastes schlegelii. It can be distinguished from Peniculus minuticaudae by the combination of a rudimentary abdomen, long neck and setae on leg 1 and from Peniculus ostraciontis by the long neck, slender trunk, and setae on leg 1. It is also shown that Peniculus truncatus captured from the same host in Korea was misidentified as Peniculus ostraciontis and hence, this is thesecond record of the occurrence of Peniculus truncatus in Korea. A key is provided for the 14 nominal species of Peniculus.

Two New Species Belonging to the Dentipes- and Conifera-Subgroups of Triconia (Copepoda: Cyclopoida: Oncaeidae) from the East China Sea

ABSTRACT Two new species of Triconia in Oncaeidae, including both sexes of Triconia constricta n. sp. and females of Triconia pararedacta n. sp., are described from south of Jeju Island in the East China Sea. Triconia constricta belongs to the dentipes-subgroup of Triconia characterized by the absence of integumental pockets on the anterior surface of the labrum. It is distinguished from the closely related species of this subgroup, T. dentipes (Giesbrecht, 1891), T. elongata Böttger-Schnack, 1999, and T. giesbrechti Böttger-Schnack, 1999, by the following combination of morphological features in females: 1) lateral margins of genital double-somite in dorsal view slightly constricted at midlength; 2) P5 with very long outer basal seta, reaching beyond paired secretory pores on posterior part of genital double-somite, as well as distinctive length ratios of exopodal setae; in both sexes; 3) length ratios of caudal setae, and 4) relative spine lengths on distal endopodal segments of swimming legs 2 to 4. Triconia pararedacta is a member of the conifera-subgroup characterized by a dorsal projection on the second pedigerous somite in the female. It differs from females of other species of this subgroup in the following: 1) very small-sized dorsal projection on second pedigerous somite, 2) different length to width ratio of P5 exopod, 3) relative lengths of outer basal seta and exopodal setae of P5, and 4) different length ratio of outer distal spine to distal spine on endopods of P2–P4. Additional character states are proposed for defining the dentipes-subgroup within Triconia and for recognizing three sets of species within the conifera-subgroup.

Species of Triconia of the conifera-Subgroup (Copepoda, Oncaeidae) from Korean waters, Including a New Species

Abstract Three species of Triconia belonging to the conifera-subgroup are described from Korean waters (NW Pacific). A new species, Triconia hirsuta, was found that can be distinguished from its sibling T. conifera by a paired patch of long setules on the anterolateral margin of the genital double-somite in the female, and an unusual position of caudal seta II branching off at almost a right angle to the caudal ramus. Males have not been found so far. Both sexes of T. conifera (Giesbrecht, 1891) and T. borealis (Sars, 1918) from Korean waters are redescribed with the addition of morphological details and/or differences not noted in earlier descriptions. Morphological characters of Korean T. conifera are in close agreement with specimens described from the Mediterranean Sea and the Pacific, but differ in several parameters from T. conifera from the Red Sea, which is regarded as a distinct, though closely related, species requiring re-examination. Published data on the community structure and zoogeographical distribution of oncaeids of the conifera-type in the NW Pacific are summarized, and the remaining uncertainties concerning the distribution of species of the conifera-subgroup in these areas are pointed out.

A new deep-water calanoid copepod and the phylogeny of the genus Nullosetigera nom. nov. in the Nullosetigeridae nom. nov. (pro Phyllopus: Phyllopodidae) from Japanese waters

Nullosetigeridae nom. nov. is proposed for Phyllopodidae Brodsky, 1950, nom. nud., and Nullosetigera nom. nov. is introduced for Phyllopus Brady, 1883, non Rafinesque, 1815. A new species, Nullosetigera auctiseta, is described from Japanese waters. Nullosetigera mutica comb. nov. (Sars, 1907) and N. mutata comb. nov. (Tanaka, 1964) are redescribed. Phylogenetic analysis implies that two groups, N. auctiseta–N. mutica group and N. mutata–N. impar–N. bidentata–N. helgae group, exist within the genus Nullosetigera and that the new species first diverges with N. mutica. The relatively advanced species, N. impar, N. bidentata, and N. helgae are the most widespread, and are vertically distributed from the epipelagic to the bathypelagic layers.