Hae-Lip Suh

Larval development of the euphausiid Euphausia pacifica in the Yellow Sea

The complete larval development of Euphausia pacifica in the Yellow Sea is described and the stages are compared with larvae of E. nana. Euphausiid larvae examined in the present study were collected at 30 stations in the Yellow Sea in 1989. During the stages of Calyptopis III to Furcilia II, E. pacifica larvae are smaller than E. nana larvae but they are larger from Furcilia III onward. There are geographical variations in body size of Calyptopis III among the southern California waters, the eastern Japan waters, the Japan Sea, and the Yellow Sea; body size is smallest in the Yellow Sea and Japan Sea, while it is largest in southern California waters and intermediate in eastern Japan waters. Segmentation of antennal endopods was observed in the 5″6 to 5″1 furcilia forms in the Yellow Sea population, suggesting that this characteristic is not as reliable for identification of furcilia stages as the pleopods and terminal telson spines. Thus, we propose here that there are six furcilia stages of E. pacifica, instead of the seven previously reported by Boden (1950).

Comparative morphology of the feeding basket of five species of Euphausia (Crustacea, Euphausiacea) in the western North Pacific, with some ecological considerations

The feeding basket morphology and stomach content analyses of five Euphausia species (E. recurva, E. nana, E. pacifica, E. mutica and E. similis) were compared to elucidate their feeding ecology. The filter areas of feeding basket of E. pacifica and E. nana were proportionally larger than those of others in the size classes 13-20 mm and <13 mm, respectively, suggesting a high filtering efficiency in these species at each size class. Based on the secondary setal distance, it is suggested that there are three types of feeding basket in five Euphausia species. One is the fine mesh (<5 μm) of E. pacifica and E. nana; a second is the medium (10-20 μm) of E. recurva and E. mutica; and the third is the coarse (20-30 μm) of E. similis. The ability to feed on particles <5 μm would give both species, E. pacifica and E. nana, a great advantage over other species when number of flagellates is high. Stomach content analyses indicated a more omnivorous feeding mode in E. mutica, E. recurva and E. similis and a more herbivorous in E. pacifica and E. nana. This is in agreement with morphological studies of feeding baskets. Increments in the primary and secondary setal distances with increasing size of four Euphausia species, except E. pacifica, were evident, reflecting interspecific differences in food particle sizes utilized. In E. pacifica, however, the morphological similarity should produce intraspecific competition in diet.

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.

MORPHOLOGY OF THE GASTRIC MILL OF THE GENUS THYSANOPODA (EUPHAUSIACEA)

The gastric mill structure has been related to utilization of food resources and to phylogenetic relationships in euphausiids. Although the possibility that species in the same genus have a gastric mill with similar morphology has been reported, it is still unclear whether this similarity is present in all species of euphausiids. Therefore, I have examined detailed morphology of the gastric mills in 8 species of Thysanopoda. The well-developed gastric mill of this genus comprises a pair of cluster spines and a pair of lateral teeth. The filter press present in Bentheuphausia amblyops is absent in all species of Thysanopoda. Comparison of the species of Thysanopoda indicated 2 different arrangements of the gastric mill with respect to presence or absence of lateral teeth. One is the well-developed gastric mill of T. cornuta, T. cristata, T. egregia, T. obtusifrons, T. spinicaudata, and T. tricuspidata; the other is the gastric mill without lateral teeth of T. acutifrons and T. aequalis. I report here that the gastric mill in Thysanopoda is diverse in morphology. On the basis of the gastric mill morphology, phylogenetic relationships of euphausiid genera are discussed.

The gastric mill of euphausiid crustaceans: a comparison of eleven species

The morphology of the gastric mill of 11 species in the family Euphausiidae is described. Two distinct arrangements can be recognized with respect to presence or absence of lateral teeth. One is the well-developed gastric mill of Thsanoessa gregaria, T. inermis, T. macrura and Pseudeuphausia sinica; the other is the gastric mill without lateral teeth of Nematoscelis atlantica, N. difficilis, N. megalops, Nematobrachion flexipes, N. sexspinosum, Stylocheiron abbreviatum, and S. carinatum. This supports the close relationships of the four species of both genera, Thysanoessa and Pseudeuphausia on the one hand and seven species belonging to Nematobrachion, Nematoscelis, and Stylocheiron on the other hand. The hypothesis that species in the same genus have similar gastric mill morphology, which was once rejected in the genus Thysanopoda, is accepted in all five genera examined here. Functional morphology of euphausiid foreguts is discussed.

ONTOGENY OF FOREGUT MORPHOLOGY IN THE EUPHAUSIID EUPHA USIA PACIFICA

ABSTRACT The ontogeny of the foregut in Euphausia pacifica was investigated by direct observations, using scanning electron microscopy with the dry fracturing method. The results show how the adult structures of the gastric mill are formed by the progressive transformation of larval structures. The gastric mill is lacking in all calyptopis stages, but the lateral process appears in calyptopis II and III. By furcilia I, the lateral process is replaced by the basic adult form of the gastric mill. The development of the gastric mill is gradual. In early furcilia stages it consists of a pair of poorly chitinized lateral teeth and a pair of undeveloped cluster spines. The number of spines on the lateral teeth increases from 2 in furcilia II to 6 in furcilia VI. The filter press does not appear in any larval stages. Significant changes in foregut morphology occur between calyptopis I and II, and between calyptopis III and furcilia I, although they do not closely follow the change of diet. It is likely, therefore, that ontogenetic changes in foregut morphology are more related to the phylogenetic history of euphausiids than to diet. Comparison of the morphology of the mandibles and the foregut for the larval stages of E. pacifica indicates that there is no inverse correlation between the mandibles and the gastric mill in masticatory ability during ontogeny.

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.

Mysidacea (Crustacea) from the Korea Strait and Its Adjacent Waters

Thirteen pelagic species of mysids, representing nine genera, are reported from the Korea Strait and its adjacent waters. Of these, seven species, Doxomysis quadrispinosa, Meterythrops microphthalma, Pleurerythrops secunda, Pseudanchialina pusilla, Siriella gracilis, S. okadai, and S. thompsoni, are newly recorded from the Korean waters. A taxonomic key and illustrative figures are given

A new species of the genus Amphiascoides (Copepoda: Harpacticoida) from Korean waters

ABSTRACT A new species, Amphiascoides coreanus, is described from the sandy beaches of Sangju-ri, Namhae, and Dolsan-do, Yeosu, the south coast of Korea. This species is clearly distinguishable from its congeners with the combined characters of the short bulbous caudal setae IV and V, three-segmented antennary exopod, and only one inner seta of the Leg 3 exopod segment 3. Additionally, the species is easily distinguishable from the congeners by the minute spinules on the dorsal body surface. The new species shares the three-segmented antennary exopod and only four setae on the third exopodal segment of Leg 3 with A. dispar and A. paradebilis but displays the characteristic shape of caudal setae. This is the first record of the genus Amphiascoides in the region.