On the Larval Development of Elminius Modestus Darwin

Abstract

Nauplii of the first two stages were obtained from adult Elminius modestus and larvae of all stages, except the smallest, were obtained from the plankton over Essex oyster beds.Over 200 nauplii of all sizes were measured. Their size distribution, plotted graphically, showed six peaks corresponding to six naupliar stages. The later stages were much more variable in size than the earlier stages.The size limits and characteristics of each naupliar stage are given. Briefly, Stage I has the fronto-lateral horns pointing backwards. Stage II has the caudal spine much longer than the abdominal process. Stage III has the abdominal process about as long as the caudal spine, but has no carapace fold posteriorly. Stage IV has a carapace fold but no sign of the abdominal appendages. Stage V has the rudiments of these appendages showing indistinctly within the abdomen. In Stage VI the abdominal appendages are prominent.

Studies on the Phylogenetic Implications of Ontogenetic Features in the Poecilostome Nauplii (Copepoda : Cyclopoida)

“…As shown in Fig. 10, the mandibular coxa with a stout spine-like process accompanied by the original coxal spine at the base is also found in the Cirripedia (see Bassindale, 1936;Knight-Jones & Waugh, 1949;Jones & Crisp, 1954;Barnes & Barnes, l959a, b;Dalley, 1984;Egan & Anderson, 1986;Achituv, 1986) and the Ascothoracida (Yosii, 1931 b). In the M ystacocarida and Cephalocarida, the coxa yields a gnathobase with toothed cutting edge, which is also accompanied by the original coxal spine near the base (see Hessler & Sanders, 1966;Sanders, 1963;Sanders & Hessler, 1963).…”

“…All cirriped nauplii studied thus far have one seta (see Fig. 10) (Groom, 1894;Bassindale, 1936;Knight-jones & Waugh, 1949;Jones & Crisp, 1954;Costlow & Bookhout, 1958;Barnes & Barnes, 1959a, b;Barker, 1976;Dalley, 1984;Egan & Anderson, 1986;Achituv, 1986). This segment has two setae in the Facetotecta (see Fig.…”

“…10), the endopod is three-segmented, though the distal joint is indistinct in most cases (see Groom, 1894;Bassindale, 1936;Pyefinch, 1948Pyefinch, , 1949Knight-Jones & Waugh, 1949;Jones & Grips, 1954;Costlow & Bookhout, 1958;Barnes & Barnes, 1959a, b;Barker, 1976;Dalley, 1984;Egan & Anderson, 1986). In the Ascothoracida, the endopod is also three-segmented, such as in Baccalaureusjaponicus ( Fig.…”

“…At any rate, the caudal process is less prevailing in the extant copepod nauplii. It can be considered that the caudal process found separately in some particular groups of Cyclopoida and Harpacticoida, excluding the uncertain structure in the lichomolgid nauplii, is homologous with the caudal spine characteristic to the nauplii of the Cirripedia (Groom, 1894;Bassindale, 1936;Pyefinch, 1948;Knight-Jones & Waugh, 1949;Jones & Grips, 1954;Costlow & Bookhout, 1958;Barnes & Barnes, 1959a, b;Barker, 1976;Dalley, 1984;Egan & Anderson, 1986;Achituv, 1986), terminal process in the Ascothoracida (Lacaze-Duthiers, 1883;Yosii, 193la, b;Okada, 1938, Grygier, 1985, caudal horn of the nauplius Y of the Facetotecta (Bresciani, 1965;Schram, 1970Schram, , 1972It6, 1986), and supra-anal process tipped with a seta of the metanauplii of the Mystacocarida (Delamare Deboutteville, 1954;Hessler & Sanders, 1966). Therefore, the caudal process may be regarded to as a primitive, or a plesiomorphic feature in the Maxillopoda.…”

“…In the Cirripedia (Fig. 10), the endopod is three-segmented, though indistinct in some forms, and has three tufts of elements; the formulae of the segments are usually 4, 3, 4 (see Bassindale, 1936;Knight-Jones & Waugh, 1949;Jones & Crisp, 1954;Costlow & Bookhout, 1958, Barnes & Barnes, l959a, b;Barker, 1976;Dalley, 1984;Egan & Anderson, 1986;Achituv, 1986). The first segment has three spines which are considered to be corresponding with the three prominent spines in the Copepoda.…”