Even the youngest larval Phyllosoma, such as has just been described, cannot be compared with a Zoaea, but belongs rather, in the possession of biramous thoracic feet, to a Mysis stage.
In a larva of about three millimetres a pair of biramous appendages arises behind the three footless thoracic segments.
It consists essentially in the fresh development of the first pair of maxillipeds and the two last ambulatory appendages, the growth and segmentation of the abdomen, and the sprouting on it of biramous swimming feet.
The six posterior pairs of appendages have grown out as functional biramous swimming feet, which can project beyond the shell and are used in the locomotion of the larva.
The five maxillipeds have the characters of normal biramous Zoaea feet.
The first pair of antennae is unusually long, and the second pair continues to function as a biramous swimming organ; the outer ramus is multiarticulate.
This portion has a dorsal shield covering the next or middle region, which consists of five segments each with a pair of biramous appendages.
That the second pair of antennae are biramous swimming feet with a hook used in mastication, and are innervated (?
It has not the typical biramous Copepod character.
Behind the second maxilliped the third maxilliped (mxp3) early appears as a small biramous appendage, and the five ambulatory feet become distinctly formed as uniramous appendages--the exopodites not being present.
The three following biramous appendages have retained their earlier characters but have become much reduced in size.
In the true Zoaea stage there appear on the five thoracic segments pouch-like biramous rudiments of the limbs.
The sixth segment of the abdomen has a pair of biramous appendages, which, with the telson, form a swimming-fan.
At the end of the last thoracic segment, there is a minute abdomen, bearing three pairs of biramous cirri.
That Cirripedes have some special affinity to the Entomostraca, may be inferred from the fewness of the cephalic appendages, the biramous legs, the state of the abdomen, and the form of the carapace.
There are always six pairs; each biramous and multiarticulated, supported on a pedicel formed of two segments.
Again, in the Thoracica there are no abdominal appendages, excepting the terminal or caudal, whereas in Cryptophialus the abdomen bears three pairs of biramous cirri.
The twenty-four extreme tips, likewise, of the six pairs of biramous cirri of the Cirripede are formed within the twenty-four extremities of the six pairs of biramous, natatory legs of the pupa.
The mandibles, like the antennae, have, in the nauplius, the form of biramous swimming limbs, with a masticatory process originating from the proximal part of the protopodite.
This form is retained, with little alteration in some adult Copepoda, where the biramous "palp" still aids in locomotion.
The eyes were probably stalked, the antennae and mandiblesbiramous and natatory, and both armed with masticatory processes.
It is highly probable, however, that the biramous limb is a simplification of a more complex primitive type, to which the Phyllopod limb is a more or less close approximation.
The limb-buds early become bilobed and grow out into typical biramous appendages which gradually assume the characters found in the adult.
In the Cirripedia (Thyrostraca) the six pairs of biramous cirriform limbs differ only slightly from each other, and in many Copepoda this is also the case.
The abdomen of the female is very broad, and has four pairs of biramous appendages covered with hairs, the normal function of which is to carry the eggs.
The effect of the parasite in the male is that the abdomen is broader, the copulatory styles reduced, and biramous hairy appendages are developed similar to those of the female, but smaller.
Either condition might develop from the generalized biramous antennas of Trilobita, but the present evidence indicates a tendency toward obsolescence.
There are twenty-four pairs of biramous thoracic appendages, which lack endobases.
As pointed out in the case of Calymene and Ceraurus, the trilobites show a tendency toward the degeneration of the first and second pairs of biramous appendages, particularly of the gnathobases.
The limbs of most Crustacea are readily explained as modifications of a simple biramous type.
The chief primitive characteristics of trilobites are: direct development from a protaspis common to the subclass; variability in the number of segments, position of the mouth, and type of eyes; and serially similar biramous appendages.
From similar opisthoparian ancestors there were, however, derived primitive Malacostraca retaining biramous antennae, but with a carapace and reduced pleural lobes and pygidium.
There are four pairs of biramous cephalic appendages, which differ only very slightly from the appendages of the thorax.
Very little comparison can be made between the Ostracoda and Trilobita, other than in the ground-plan of the limbs, but the presence of biramous antennae is a primitive characteristic.
In Doctor Walcott's restoration of Calymene he has represented all four pairs of biramous appendages as articulating back of the posterior end of the hypostoma.
The crustacean characteristics are seen in the presence of five, instead of six, pairs of appendages on the head, the first of which are multisegmented antennules, and in the biramous appendages on the body of Emeraldella.
The maxillulae are likewise biramous but much modified.
Crustacea with more or less eurypterid-like form, one pair of uniramous antennae, biramous appendages on anterior part of trunk, modified endopodites on cephalon.
It does not appear that the appendages of Insects conform to the biramous Crustacean type, though the ends of the maxillæ are often divided into an outer and an inner portion.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "biramous" in a variety of sentences. We hope that you will now be able to make sentences using this word.
