Calanoidea: Families

J.M. Bradford-Grieve


Metridinidae Sars, 1902

Description. Female. Rostrum with 2 filaments; rostral margin extends into 1 blunt protrusion, or not extended. Cephalosome and pedigerous somite 1 separate; pedigerous somites 4 and 5 separate. Posterior corners of prosome in lateral view bluntly rounded, or with 1 acute point, or triangular or obtusely pointed; dorsal view symmetrical. Urosome with 3 free somites. Genital double-somite symmetrical in dorsal view; gonopores not covered by genital operculum; with pair of seminal receptacles, or with one seminal receptacle; with single copulatory pore on surface of somite, or with pair of copulatory pores on surface of somite. Caudal rami symmetrical, or asymmetrical.

Mouthparts. Antenna 1 with 23-24 free segments; ancestral segments X and XI partly fused. Antenna 2 exopod with 7 free segments; 9-11 setae; basis and endopod separate. Mandible basis with 4 setae; endopod terminal segment with 10 setae. Maxilla 1 basal exite seta present; exopod extends short of endopod distal border. Maxilla 2 coxal epipodite seta absent. Maxilliped coxal endite 2 with 4 setae.

Legs. Leg 1 basis outer seta present; endopod with 3 segments; exopod with 3 segments; exopod segment 1 with outer distal spine; exopod segment 3 with 4 inner setae. Leg 2 endopod with 3 segments; segment 1 excavated; exopod with 3 segments; exopod segment 3 with 3 outer spines. Leg 3 basis outer distal spine absent; endopod segment 3 with 8 setae. Legs 3 and 4 endopod with 3 segments; exopod with 3 segments; exopod segment 3 with 3 outer spines; exopod segment 3 with 5 inner setae. Leg 4 endopod segment 3 with 7 setae. Legs 2-4 surfaces naked; terminal spine with outer border serrated. Leg 5 present; very dissimilar from legs 2-4; coxa inner border without seta; uniramous, small, symmetrical 2-segmented, coxae and intercoxal sclerite fused, basis and exopod segment 1 usually with outer edge seta and spine respectively, exopod segment 2 with 2-4 setae, terminal exopod segments may be fused.

Mode of life. Pelagic, in oceanic waters.

Depth distribution. Epipelagic (0-500 m), or mesopelagic (500-1000 m), or bathypelagic (greater than 1000 m).

Generic composition. This family contains 3 genera: Gaussia Wolfenden, 1905; Metridia Boeck, 1865; Pleuromamma Giesbrecht, 1898.


(Variant) Male (sexually dimorphic characters).

Description. Male. Pedigerous somites 4 and 5 fused or partly fused. Posterior corners of prosome in lateral view bluntly rounded, or triangular or obtusely pointed. Urosome symmetrical in dorsal view, or asymmetrical in dorsal view.

Mouthparts. Mouthparts well-developed. Antenna 1 geniculate on left. Maxilliped endopod segments 5 and 6 with outer setae normal.

Legs. Right leg 5 uniramous; exopod usually 2-3-segmented, segment 2 with an inner spinous process in some genera, segment 3 with 1 or 2 minute distal setae. Left leg 5 uniramous; exopod 2-3-segmented, segment 1 bearing curved inner process, distal segment swollen, often curved and claw-like.



Cite this publication as: 'Bradford-Grieve, J.M. (2002 onwards). Calanoida: families. Version 1: 2 October 2002. http://crustacea.net'.